PCEP Extensions for Stateful PCE
draft-ietf-pce-stateful-pce-05
The information below is for an old version of the document.
| Document | Type |
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| Authors | Edward Crabbe , Jan Medved , Ina Minei , Robert Varga | ||
| Last updated | 2013-07-01 | ||
| Replaces | draft-crabbe-pce-stateful-pce | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-pce-stateful-pce-05
Network Working Group E. Crabbe
Internet-Draft Google, Inc.
Intended status: Standards Track J. Medved
Expires: January 1, 2014 Cisco Systems, Inc.
I. Minei
Juniper Networks, Inc.
R. Varga
Pantheon Technologies SRO
June 30, 2013
PCEP Extensions for Stateful PCE
draft-ietf-pce-stateful-pce-05
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests.
Although PCEP explicitly makes no assumptions regarding the
information available to the PCE, it also makes no provisions for
synchronization or PCE control of timing and sequence of path
computations within and across PCEP sessions. This document
describes a set of extensions to PCEP to enable stateful control of
MPLS-TE and GMPLS LSPs via PCEP.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 1, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation and Objectives for Stateful PCE . . . . . . . . . . 7
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1.1. Background . . . . . . . . . . . . . . . . . . . . . . 7
3.1.2. Why a Stateful PCE? . . . . . . . . . . . . . . . . . 8
3.1.3. Protocol vs. Configuration . . . . . . . . . . . . . . 15
3.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 15
4. New Functions to Support Stateful PCEs . . . . . . . . . . . . 16
5. Architectural Overview of Protocol Extensions . . . . . . . . 17
5.1. LSP State Ownership . . . . . . . . . . . . . . . . . . . 17
5.2. New Messages . . . . . . . . . . . . . . . . . . . . . . . 17
5.3. Capability Negotiation . . . . . . . . . . . . . . . . . . 18
5.4. State Synchronization . . . . . . . . . . . . . . . . . . 19
5.4.1. State Synchronization Avoidance . . . . . . . . . . . 21
5.4.2. PCE-triggered State Synchronization . . . . . . . . . 25
5.5. LSP Delegation . . . . . . . . . . . . . . . . . . . . . . 25
5.5.1. Delegating an LSP . . . . . . . . . . . . . . . . . . 26
5.5.2. Revoking a Delegation . . . . . . . . . . . . . . . . 27
5.5.3. Returning a Delegation . . . . . . . . . . . . . . . . 28
5.5.4. Redundant Stateful PCEs . . . . . . . . . . . . . . . 29
5.5.5. Redelegation on PCE failure . . . . . . . . . . . . . 29
5.6. LSP Operations . . . . . . . . . . . . . . . . . . . . . . 30
5.6.1. Passive Stateful PCE Path Computation
Request/Response . . . . . . . . . . . . . . . . . . . 30
5.6.2. Active Stateful PCE LSP Update . . . . . . . . . . . . 32
5.7. LSP Protection . . . . . . . . . . . . . . . . . . . . . . 33
5.8. Transport . . . . . . . . . . . . . . . . . . . . . . . . 33
6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1. The PCRpt Message . . . . . . . . . . . . . . . . . . . . 34
6.2. The PCUpd Message . . . . . . . . . . . . . . . . . . . . 35
6.3. The PCErr Message . . . . . . . . . . . . . . . . . . . . 36
6.4. The PCReq Message . . . . . . . . . . . . . . . . . . . . 37
6.5. The PCRep Message . . . . . . . . . . . . . . . . . . . . 37
7. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 38
7.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 38
7.1.1. Stateful PCE Capability TLV . . . . . . . . . . . . . 38
7.1.2. LSP State Database Version TLV . . . . . . . . . . . . 39
7.1.3. PCE Redundancy Group Identifier TLV . . . . . . . . . 40
7.2. SRP Object . . . . . . . . . . . . . . . . . . . . . . . . 40
7.3. LSP Object . . . . . . . . . . . . . . . . . . . . . . . . 41
7.3.1. LSP Identifiers TLVs . . . . . . . . . . . . . . . . . 44
7.3.2. Symbolic Path Name TLV . . . . . . . . . . . . . . . . 46
7.3.3. LSP Error Code TLV . . . . . . . . . . . . . . . . . . 47
7.3.4. RSVP Error Spec TLV . . . . . . . . . . . . . . . . . 48
7.3.5. LSP State Database Version TLV . . . . . . . . . . . . 48
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7.3.6. Delegation Parameters TLVs . . . . . . . . . . . . . . 49
7.4. Optional TLVs for the LSPA Object . . . . . . . . . . . . 49
7.4.1. Symbolic Path Name TLV . . . . . . . . . . . . . . . . 49
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
8.1. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 49
8.2. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . 50
8.3. LSP Object . . . . . . . . . . . . . . . . . . . . . . . . 50
8.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 50
8.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . . 51
8.6. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 52
8.7. LSP-ERROR-CODE TLV . . . . . . . . . . . . . . . . . . . . 52
8.8. LSP-SIG-TYPE field in the LSP object . . . . . . . . . . . 52
9. Manageability Considerations . . . . . . . . . . . . . . . . . 53
9.1. Control Function and Policy . . . . . . . . . . . . . . . 53
9.2. Information and Data Models . . . . . . . . . . . . . . . 54
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 54
9.4. Verifying Correct Operation . . . . . . . . . . . . . . . 54
9.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . . 54
9.6. Impact on Network Operation . . . . . . . . . . . . . . . 55
10. Security Considerations . . . . . . . . . . . . . . . . . . . 55
10.1. Vulnerability . . . . . . . . . . . . . . . . . . . . . . 55
10.2. LSP State Snooping . . . . . . . . . . . . . . . . . . . . 55
10.3. Malicious PCE . . . . . . . . . . . . . . . . . . . . . . 56
10.4. Malicious PCC . . . . . . . . . . . . . . . . . . . . . . 56
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 56
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 57
12.1. Normative References . . . . . . . . . . . . . . . . . . . 57
12.2. Informative References . . . . . . . . . . . . . . . . . . 58
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 59
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1. Introduction
[RFC5440] describes the Path Computation Element Protocol (PCEP.
PCEP defines the communication between a Path Computation Client
(PCC) and a Path Control Element (PCE), or between PCE and PCE,
enabling computation of Multiprotocol Label Switching (MPLS) for
Traffic Engineering Label Switched Path (TE LSP) characteristics.
Extensions for support of GMPLS in PCEP are defined in
[I-D.ietf-pce-gmpls-pcep-extensions]
This document specifies a set of extensions to PCEP to enable
stateful control of LSPs between and across PCEP sessions in
compliance with [RFC4657]. It includes mechanisms to effect LSP
state synchronization between PCCs and PCEs, delegation of control
over LSPs to PCEs, and PCE control of timing and sequence of path
computations within and across PCEP sessions.
2. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer.
This document uses the following terms defined in [RFC4655]: TED.
This document uses the following terms defined in [RFC4090]: MPLS TE
Fast Reroute (FRR), FRR One-to-One Backup, FRR Facility Backup.
The following terms are defined in this document:
Stateful PCE: has access to not only the network state, but also to
the set of active paths and their reserved resources for its
computations. A stateful PCE might also retain information
regarding LSPs under construction in order to reduce churn and
resource contention. The additional state allows the PCE to
compute constrained paths while considering individual LSPs and
their interactions. Note that this requires reliable state
synchronization mechanisms between the PCE and the network, PCE
and PCC, and between cooperating PCEs.
Passive Stateful PCE: uses LSP state information learned from PCCs
to optimize path computations. It does not actively update LSP
state. A PCC maintains synchronization with the PCE.
Active Stateful PCE: is an extension of Passive Stateful PCE, in
which the PCE may issue recommendations to the network. For
example, an active stateful PCE may utilize the Delegation
mechanism to update LSP parameters in those PCCs that delegated
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control over their LSPs to the PCE.
Delegation: An operation to grant a PCE temporary rights to modify a
subset of LSP parameters on one or more PCC's LSPs. LSPs are
delegated from a PCC to a PCE, and are referred to as delegated
LSPs. The PCC who owns the PCE state for the LSP has the right to
delegate it. An LSP is owned by a single PCC at any given point
in time.
Revocation An operation performed by a PCC on a previously delegated
LSP. Revocation revokes the rights granted to the PCE in the
delegation operation.
Redelegation Timeout Interval: when a PCEP session is terminated, a
PCC waits for this time period before revoking LSP delegation to a
PCE and attempting to redelegate LSPs associated with the
terminated PCEP session to an alternate PCE. The Redelegation
Timeout Interval is a PCC-local value that can be either operator-
configured or dynamically computed by the PCC based on local
policy.
State Timeout Interval: when a PCEP session is terminated, a PCC
waits for this time period before flushing LSP state associated
with that PCEP session and reverting to operator-defined default
parameters. The state will not be flushed in two cases: a) the
LSP is redelegated to another PCE before the expiration of the
State Timeout Interval or b)the PCC makes changes to the LSP
state. The State Timeout Interval is a PCC-local value that can
be either operator-configured or dynamically computed by the PCC
based on local policy. The State Timeout Interval value SHOULD be
greater than or equal to the Redelegation Timeout Interval value
in order to allow for redelegation of LSPs without unnecessary
churn in or loss of state.
LSP State Report: an operation to send LSP state (Operational /
Admin Status, LSP attributes configured and set by a PCE, etc.)
from a PCC to a PCE.
LSP Update Request: an operation where an Active Stateful PCE
requests a PCC to update one or more attributes of an LSP and to
re-signal the LSP with updated attributes.
LSP Priority: a specific pair of MPLS setup and hold priority values
as defined in [RFC3209].
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LSP State Database: information about and attributes of all LSPs
that are being reported to one or more PCEs via LSP State Reports.
Minimum Cut Set: the minimum set of links for a specific source
destination pair which, when removed from the network, result in a
specific source being completely isolated from specific
destination. The summed capacity of these links is equivalent to
the maximum capacity from the source to the destination by the
max-flow min-cut theorem.
Within this document, PCE-PCE communications are described by having
the requesting PCE fill the role of a PCC. This provides a saving in
documentation without loss of function.
The message formats in this document are specified using Routing
Backus-Naur Format (RBNF) encoding as specified in [RFC5511].
3. Motivation and Objectives for Stateful PCE
Editor's note: the content in this section is duplicated in
[I-D.zhang-pce-stateful-pce-app]. To avoid loss of information, the
use cases will be removed from this document only after
[I-D.zhang-pce-stateful-pce-app] becomes a working group document.
In the meantime, changes and updates to the use cases are reflected
in [I-D.zhang-pce-stateful-pce-app].
3.1. Motivation
In the following sections, several use cases are described,
showcasing scenarios that benefit from the deployment of a stateful
PCE. The scenarios apply equally to MPLS-TE and GMPLS deployments.
3.1.1. Background
Traffic engineering has been a goal of the MPLS architecture since
its inception ([RFC3031], [RFC2702], [RFC3346]). In the traffic
engineering system provided by [RFC3630], [RFC5305], and [RFC3209]
information about network resources utilization is only available as
total reserved capacity by traffic class on a per interface basis;
individual LSP state is available only locally on each LER for its
own LSPs. In most cases, this makes good sense, as distribution and
retention of total LSP state for all LERs within in the network would
be prohibitively costly.
Unfortunately, this visibility in terms of global LSP state may
result in a number of issues for some demand patterns, particularly
within a common setup and hold priority. This issue affects online
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traffic engineering systems.
A sufficiently over-provisioned system will by definition have no
issues routing its demand on the shortest path. However, lowering
the degree to which network over-provisioning is required in order to
run a healthy, functioning network is a clear and explicit promise of
MPLS architecture. In particular, it has been a goal of MPLS to
provide mechanisms to alleviate congestion scenarios in which
"traffic streams are inefficiently mapped onto available resources;
causing subsets of network resources to become over-utilized while
others remain underutilized" ([RFC2702]).
3.1.2. Why a Stateful PCE?
[RFC4655] defines a stateful PCE to be one in which the PCE maintains
"strict synchronization between the PCE and not only the network
states (in term of topology and resource information), but also the
set of computed paths and reserved resources in use in the network."
[RFC4655] also expressed a number of concerns with regard to a
stateful PCE, specifically:
o Any reliable synchronization mechanism would result in significant
control plane overhead
o Out-of-band TED synchronization would be complex and prone to race
conditions
o Path calculations incorporating total network state would be
highly complex
In general, stress on the control plane will be directly proportional
to the size of the system being controlled and the tightness of the
control loop, and indirectly proportional to the amount of over-
provisioning in terms of both network capacity and reservation
overhead.
Despite these concerns in terms of implementation complexity and
scalability, several TE algorithms exist today that have been
demonstrated to be extremely effective in large TE systems, providing
both rapid convergence and significant benefits in terms of
optimality of resource usage [MXMN-TE]. All of these systems share
at least two common characteristics: the requirement for both global
visibility of a flow (or in this case, a TE LSP) state and for
ordered control of path reservations across devices within the system
being controlled. While some approaches have been suggested in order
to remove the requirements for ordered control (See [MPLS-PC]), these
approaches are highly dependent on traffic distribution, and do not
allow for multiple simultaneous LSP priorities representing diffserv
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classes.
The following use cases demonstrate a need for visibility into global
inter-PCC LSP state in PCE path computations, and for a PCE control
of sequence and timing in altering LSP path characteristics within
and across PCEP sessions. Reference topologies for the use cases
described later in this section are shown in Figures 1 and 2.
Unless otherwise cited, use cases assume that all LSPs listed exist
at the same LSP priority.
+-------+
| A |
| |
+-------+
\
+-------+ +-------+
| C |-------------------------| E |
| | | |
+-------+ +-------+ +-------+
/ \ | D | /
+-------+ ------| |------
| B | +-------+
| |
+-------+
Figure 1: Reference topology 1
+-------+ +-------+ +-------+
| A | | B | | C |
| | | | | |
+---+---+ +---+---+ +---+---+
| | |
| | |
+---+---+ +---+---+ +---+---+
| E | | F | | G |
| +--------+ +--------+ |
+-------+ +-------+ +-------+
Figure 2: Reference topology 2
3.1.2.1. Throughput Maximization and Bin Packing
Because LSP attribute changes in [RFC5440] are driven by PCReq
messages under control of a PCC's local timers, the sequence of RSVP
reservation arrivals occurring in the network will be randomized.
This, coupled with a lack of global LSP state visibility on the part
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of a stateless PCE may result in suboptimal throughput in a given
network topology.
Reference topology 2 in Figure 2 and Tables 1 and 2 show an example
in which throughput is at 50% of optimal as a result of lack of
visibility and synchronized control across PCC's. In this scenario,
the decision must be made as to whether to route any portion of the
E-G demand, as any demand routed for this source and destination will
decrease system throughput.
+------+--------+----------+
| Link | Metric | Capacity |
+------+--------+----------+
| A-E | 1 | 10 |
| B-F | 1 | 10 |
| C-G | 1 | 10 |
| E-F | 1 | 10 |
| F-G | 1 | 10 |
+------+--------+----------+
Table 1: Link parameters for Throughput use case
+------+-----+-----+-----+--------+----------+-------+
| Time | LSP | Src | Dst | Demand | Routable | Path |
+------+-----+-----+-----+--------+----------+-------+
| 1 | 1 | E | G | 10 | Yes | E-F-G |
| 2 | 2 | A | B | 10 | No | --- |
| 3 | 1 | F | C | 10 | No | --- |
+------+-----+-----+-----+--------+----------+-------+
Table 2: Throughput use case demand time series
In many cases throughput maximization becomes a bin packing problem.
While bin packing itself is an NP-hard problem, a number of common
heuristics which run in polynomial time can provide significant
improvements in throughput over random reservation event
distribution, especially when traversing links which are members of
the minimum cut set for a large subset of source destination pairs.
Tables 3 and 4 show a simple use case using Reference Topology 1 in
Figure 1, where LSP state visibility and control of reservation order
across PCCs would result in significant improvement in total
throughput.
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+------+--------+----------+
| Link | Metric | Capacity |
+------+--------+----------+
| A-C | 1 | 10 |
| B-C | 1 | 10 |
| C-E | 10 | 5 |
| C-D | 1 | 10 |
| D-E | 1 | 10 |
+------+--------+----------+
Table 3: Link parameters for Bin Packing use case
+------+-----+-----+-----+--------+----------+---------+
| Time | LSP | Src | Dst | Demand | Routable | Path |
+------+-----+-----+-----+--------+----------+---------+
| 1 | 1 | A | E | 5 | Yes | A-C-D-E |
| 2 | 2 | B | E | 10 | No | --- |
+------+-----+-----+-----+--------+----------+---------+
Table 4: Bin Packing use case demand time series
3.1.2.2. Deadlock
Most existing RSVP-TE implementations will not tear down established
LSPs in the event of the failure of the bandwidth increase procedure
detailed in [RFC3209]. This behavior is directly implied to be
correct in [RFC3209] and is often desirable from an operator's
perspective, because either a) the destination prefixes are not
reachable via any means other than MPLS or b) this would result in
significant packet loss as demand is shifted to other LSPs in the
overlay mesh.
In addition, there are currently few implementations offering ingress
admission control at the LSP level. Again, having ingress admission
control on a per LSP basis is not necessarily desirable from an
operational perspective, as a) one must over-provision LSPs
significantly in order to avoid deleterious effects resulting from
stacked transport and flow control systems and b) there is currently
no efficient commonly available northbound interface for dynamic
configuration of per LSP ingress admission control (such an interface
could easily be defined using the extensions present in this spec,
but it beyond the scope of the current document).
Lack of ingress admission control coupled with the behavior in
[RFC3209] effectively results in mis-signaled LSPs during periods of
contention for network capacity between LSPs in a given LSP priority.
This in turn causes information loss in the TED with regard to actual
network state, resulting in LSPs sharing common network interfaces
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with mis-signaled LSPs operating in a degraded state for significant
periods of time, even when unused network capacity may potentially be
available.
Reference Topology 1 in Figure 1 and Tables 5 and 6 show a use case
that demonstrates this behavior. Two LSPs, LSP 1 and LSP 2 are
signaled with demand 2 and routed along paths A-C-D-E and B-C-D-E
respectively. At a later time, the demand of LSP 1 increases to 20.
Under such a demand, the LSP cannot be resignaled. However, the
existing LSP will not be torn down. In the absence of ingress
policing, traffic on LSP 1 will cause degradation for traffic of LSP
2 (due to oversubscription on the links C-D and D-E), as well as
information loss in the TED with regard to the actual network state.
The problem could be easily ameliorated by global visibility of LSP
state coupled with PCC- external demand measurements and placement of
two LSPs on disjoint links. Note that while the demand of 20 for LSP
1 could never be satisfied in the given topology, what could be
achieved would be isolation from the ill-effects of the
(unsatisfiable) increased demand.
+------+--------+----------+
| Link | Metric | Capacity |
+------+--------+----------+
| A-C | 1 | 10 |
| B-C | 1 | 10 |
| C-E | 10 | 5 |
| C-D | 1 | 10 |
| D-E | 1 | 10 |
+------+--------+----------+
Table 5: Link parameters for the 'Deadlock' example
+------+-----+-----+-----+--------+----------+---------+
| Time | LSP | Src | Dst | Demand | Routable | Path |
+------+-----+-----+-----+--------+----------+---------+
| 1 | 1 | A | E | 2 | Yes | A-C-D-E |
| 2 | 2 | B | E | 2 | Yes | B-C-D-E |
| 3 | 1 | A | E | 20 | No | --- |
+------+-----+-----+-----+--------+----------+---------+
Table 6: Deadlock LSP and demand time series
3.1.2.3. Minimum Perturbation
As a result of both the lack of visibility into global LSP state and
the lack of control over event ordering across PCE sessions,
unnecessary perturbations may be introduced into the network by a
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stateless PCE. Tables 7 and 8 show an example of an unnecessary
network perturbation using Reference Topology 1 in Figure 1. In this
case an unimportant (high LSP priority value) LSP (LSP1) is first set
up along the shortest path. At time 2, which is assumed to be
relatively close to time 1, a second more important (lower LSP-
priority value) LSP is established, preempting LSP 1 and shifting it
to the longer A-C-E path.
+------+--------+----------+
| Link | Metric | Capacity |
+------+--------+----------+
| A-C | 1 | 10 |
| B-C | 1 | 10 |
| C-E | 10 | 10 |
| C-D | 1 | 10 |
| D-E | 1 | 10 |
+------+--------+----------+
Table 7: Link parameters for the 'Minimum-Perturbation' example
+------+-----+-----+-----+--------+----------+----------+---------+
| Time | LSP | Src | Dst | Demand | LSP Prio | Routable | Path |
+------+-----+-----+-----+--------+----------+----------+---------+
| 1 | 1 | A | E | 7 | 7 | Yes | A-C-D-E |
| 2 | 2 | B | E | 7 | 0 | Yes | B-C-D-E |
| 3 | 1 | A | E | 7 | 7 | Yes | A-C-E |
+------+-----+-----+-----+--------+----------+----------+---------+
Table 8: Minimum-Perturbation LSP and demand time series
3.1.2.4. Predictability
Randomization of reservation events caused by lack of control over
event ordering across PCE sessions results in poor predictability in
LSP routing. An offline system applying a consistent optimization
method will produce predictable results to within either the boundary
of forecast error when reservations are over-provisioned by
reasonable margins or to the variability of the signal and the
forecast error when applying some hysteresis in order to minimize
churn.
Reference Topology 1 and Tables 9, 10 and 11 show the impact of event
ordering and predictability of LSP routing.
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+------+--------+----------+
| Link | Metric | Capacity |
+------+--------+----------+
| A-C | 1 | 10 |
| B-C | 1 | 10 |
| C-E | 1 | 10 |
| C-D | 1 | 10 |
| D-E | 1 | 10 |
+------+--------+----------+
Table 9: Link parameters for the 'Predictability' example
+------+-----+-----+-----+--------+----------+---------+
| Time | LSP | Src | Dst | Demand | Routable | Path |
+------+-----+-----+-----+--------+----------+---------+
| 1 | 1 | A | E | 7 | Yes | A-C-E |
| 2 | 2 | B | E | 7 | Yes | B-C-D-E |
+------+-----+-----+-----+--------+----------+---------+
Table 10: Predictability LSP and demand time series 1
+------+-----+-----+-----+--------+----------+---------+
| Time | LSP | Src | Dst | Demand | Routable | Path |
+------+-----+-----+-----+--------+----------+---------+
| 1 | 2 | B | E | 7 | Yes | B-C-E |
| 2 | 1 | A | E | 7 | Yes | A-C-D-E |
+------+-----+-----+-----+--------+----------+---------+
Table 11: Predictability LSP and demand time series 2
3.1.2.5. Global Concurrent Optimization
Global Concurrent Optimization (GCO) defined in [RFC5557] is a
network optimization mechanism that is able to simultaneously
consider the entire topology of the network and the complete set of
existing TE LSPs and their existing constraints, and look to optimize
or reoptimize the entire network to satisfy all constraints for all
TE LSPs. It allows for bulk path computations in order to avoid
blocking problems and to achieve more optimal network-wide solutions.
Global control of LSP operation sequence in [RFC5557] is predicated
on the use of what is effectively a stateful (or semi-stateful) NMS.
The NMS can be either not local to the switch, in which case another
northbound interface is required for LSP attribute changes, or local/
collocated, in which case there are significant issues with
efficiency in resource usage. Stateful PCE adds a few features that:
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o Roll the NMS visibility into the PCE and remove the requirement
for an additional northbound interface
o Allow the PCE to determine when re-optimization is needed
o Allow the PCE to determine which LSPs should be re-optimized
o Allow a PCE to control the sequence of events across multiple
PCCs, allowing for bulk (and truly global) optimization, LSP
shuffling etc.
3.1.3. Protocol vs. Configuration
Note that existing configuration tools and protocols can be used to
set LSP state. However, this solution has several shortcomings:
o Scale & Performance: configuration operations often require
processing of additional configuration portions beyond the state
being directly acted upon, with corresponding cost in CPU cycles,
negatively impacting both PCC stability LSP update rate capacity.
o Scale & Performance: configuration operations often have
transactional semantics which are typically heavyweight and
require additional CPU cycles, negatively impacting PCC update
rate capacity.
o Security: opening up a configuration channel to a PCE would allow
a malicious PCE to take over a PCC. The PCEP extensions described
in this document only allow a PCE control over a very limited set
of LSP attributes.
o Interoperability: each vendor has a proprietary information model
for configuring LSP state, which prevents interoperability of a
PCE with PCCs from different vendors. The PCEP extensions
described in this document allow for a common information model
for LSP state for all vendors.
o Efficient State Synchronization: configuration channels may be
heavyweight and unidirectional, therefore efficient state
synchronization between a PCE and a PCE may be a problem.
3.2. Objectives
The objectives for the protocol extensions to support stateful PCE
described in this document are as follows:
o Allow a single PCC to interact with a mix of stateless and
stateful PCEs simultaneously using the same PCEP.
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o Support efficient LSP state synchronization between the PCC and
one or more active or passive stateful PCEs.
o Allow a PCC to delegate control of its LSPs to an active stateful
PCE such that a single LSP is under the control a single PCE at
any given time. A PCC may revoke this delegation at any time
during the lifetime of the LSP. If LSP delegation is revoked
while the PCEP session is up, the PCC MUST notify the PCE about
the revocation. A PCE may return an LSP delegation at any point
during the lifetime of the PCEP session.
o Allow a PCE to control computation timing and update timing across
all LSPs that have been delegated to it.
o Enable uninterrupted operation of PCC's LSPs in the event PCE
failure or while control of LSPs is being transferred between
PCEs.
4. New Functions to Support Stateful PCEs
Several new functions will be required in PCEP to support stateful
PCEs. A function can be initiated either from a PCC towards a PCE
(C-E) or from a PCE towards a PCC (E-C). The new functions are:
Capability negotiation (E-C,C-E): both the PCC and the PCE must
announce during PCEP session establishment that they support PCEP
Stateful PCE extensions defined in this document.
LSP state synchronization (C-E): after the session between the PCC
and a stateful PCE is initialized, the PCE must learn the state of
a PCC's LSPs before it can perform path computations or update LSP
attributes in a PCC.
LSP Update Request (E-C): A PCE requests modification of attributes
on a PCC's LSP.
LSP State Report (C-E): a PCC sends an LSP state report to a PCE
whenever the state of an LSP changes.
LSP control delegation (C-E,E-C): a PCC grants to a PCE the right to
update LSP attributes on one or more LSPs; the PCE becomes the
authoritative source of the LSP's attributes as long as the
delegation is in effect (See Section 5.5); the PCC may withdraw
the delegation or the PCE may give up the delegation at any time.
[I-D.sivabalan-pce-disco-stateful] defines the extensions needed to
support autodiscovery of stateful PCEs when using OSPF ([RFC5088]) or
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IS-IS ([RFC5089]) for PCE discovery.
5. Architectural Overview of Protocol Extensions
5.1. LSP State Ownership
In the PCEP protocol (defined in [RFC5440]), LSP state and operation
are under the control of a PCC (a PCC may be an LSR or a management
station). Attributes received from a PCE are subject to PCC's local
policy. The PCEP protocol extensions described in this document do
not change this behavior.
An active stateful PCE may have control of a PCC's LSPs be delegated
to it, but the LSP state ownership is retained by the PCC. In
particular, in addition to specifying values for LSP's attributes, an
active stateful PCE also decides when to make LSP modifications.
Retaining LSP state ownership on the PCC allows for:
o a PCC to interact with both stateless and stateful PCEs at the
same time
o a stateful PCE to only modify a small subset of LSP parameters,
i.e. to set only a small subset of the overall LSP state; other
parameters may be set by the operator through CLI commands
o a PCC to revert delegated LSP to an operator-defined default or to
delegate the LSPs to a different PCE, if the PCC get disconnected
from a PCE with currently delegated LSPs
5.2. New Messages
In this document, we define the following new PCEP messages:
Path Computation State Report (PCRpt): a PCEP message sent by a PCC
to a PCE to report the status of one or more LSPs. Each LSP
Status Report in a PCRpt message can contain the actual LSP's
path,bandwidth, operational and administrative status, etc. An
LSP Status Report carried on a PCRpt message is also used in
delegation or revocation of control of an LSP to/from a PCE. The
PCRpt message is described in Section 6.1.
Path Computation Update Request (PCUpd): a PCEP message sent by a
PCE to a PCC to update LSP parameters, on one or more LSPs. Each
LSP Update Request on a PCUpd message MUST contain all LSP
parameters that a PCE wishes to set for a given LSP. An LSP
Update Request carried on a PCUpd message is also used to return
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LSP delegations if at any point PCE no longer desires control of
an LSP. The PCUpd message is described in Section 6.2.
The new functions defined in Section 4 are mapped onto the new
messages as shown in the following table.
+----------------------------------------+--------------------------+
| Function | Message |
+----------------------------------------+--------------------------+
| Capability Negotiation (E-C,C-E) | Open |
| State Synchronization (C-E) | PCRpt |
| LSP State Report (C-E) | PCRpt |
| LSP Control Delegation (C-E,E-C) | PCRpt, PCUpd |
| LSP Update Request (E-C) | PCUpd |
| ISIS stateful capability advertisement | ISIS PCE-CAP-FLAGS |
| | sub-TLV |
| OSPF stateful capability advertisement | OSPF RI LSA, PCE TLV, |
| | PCE-CAP-FLAGS sub-TLV |
+----------------------------------------+--------------------------+
Table 12: New Function to Message Mapping
5.3. Capability Negotiation
During PCEP Initialization Phase, PCEP Speakers (PCE pr PCC)
negotiate the use of stateful PCEP extensions. A PCEP Speaker
includes the "Stateful PCE Capability" TLV, described in
Section 7.1.1, in the OPEN Object to advertise its support for PCEP
stateful extensions. The Stateful Capability TLV includes the 'LSP
Update' Flag that indicates whether the PCEP Speaker supports LSP
parameter updates.
The presence of the Stateful PCE Capability TLV in PCC's OPEN Object
indicates that the PCC is willing to send LSP State Reports whenever
LSP parameters or operational status changes.
The presence of the Stateful PCE Capability TLV in PCE's OPEN message
indicates that the PCE is interested in receiving LSP State Reports
whenever LSP parameters or operational status changes.
The PCEP protocol extensions for stateful PCEs MUST NOT be used if
one or both PCEP Speakers have not included the Stateful PCE
Capability TLV in their respective OPEN message. If the PCEP
Speakers support the extensions of this draft, then a PCErr with code
"Stateful PCE capability not negotiated" (see Section 8.4) will be
generated and the PCEP session will be terminated.
LSP delegation and LSP update operations defined in this document MAY
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only be used if both PCEP Speakers set the LSP-UPDATE Flag in the
"Stateful Capability" TLV to 'Updates Allowed (U Flag = 1)'. If this
is not the case and LSP delegation or LSP update operations are
attempted, then a PCErr with code "Delegation not negotiated" (see
Section 8.4) SHOULD be generated. Note that even if the update
capability has not been negotiated, a PCE can still receive LSP
Status Reports from a PCC and build and maintain an up to date view
of the state of the PCC's LSPs.
5.4. State Synchronization
The purpose of State Synchronization is to provide a checkpoint-in-
time state replica of a PCC's LSP state in a PCE. State
Synchronization is performed immediately after the Initialization
phase ([RFC5440]).
During State Synchronization, a PCC first takes a snapshot of the
state of its LSPs state, then sends the snapshot to a PCE in a
sequence of LSP State Reports. Each LSP State Report sent during
State Synchronization has the SYNC Flag in the LSP Object set to 1.
The set of LSPs for which state is synchronized with a PCE is
determined by negotiated stateful PCEP capabilities and PCC's local
configuration (see more details in Section 9.1).
The end of synchronization marker is a PCRpt message with the SYNC
Flag set to 0 for an LSP Object with PLSP-ID equal to the reserved
value 0. The LSP Object does not include the SYMBOLIC-PATH-NAME TLV
in this case. If both PCEP speakers had set the INCLUDE-DB-VERSION
Flag in the OPEN object's STATEFUL-PCE-CAPABILITY TLV, then the LSP-
DB-VERSION TLV MUST be included and contain the PCC's latest LSP
State Database version.
A PCE SHOULD NOT send PCUpd messages to a PCC before State
Synchronization is complete. A PCC SHOULD NOT send PCReq messages to
a PCE before State Synchronization is complete. This is to allow the
PCE to get the best possible view of the network before it starts
computing new paths.
If the PCC encounters a problem which prevents it from completing the
state transfer, it MUST send a PCErr message to the PCE and terminate
the session using the PCEP session termination procedure.
In the event of a PCC resetting the session during synchronization,
the PCE MUST clean up state it received from this PCC. Session
reestablishment MUST be re-attempted per the procedures defined in
[RFC5440].
The PCE does not send positive acknowledgements for properly received
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synchronization messages. It MUST respond with a PCErr message
indicating "PCRpt error" (see Section 8.4) if it encounters a problem
with the LSP State Report it received from the PCC. Either the PCE
or the PCC MAY terminate the session if the PCE encounters a problem
during the synchronization.
The successful State Synchronization sequence is shown in Figure 3.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->| (Sync start)
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-----PCRpt, SYNC=1----->| (Sync done)
| . |
| . |
| . |
| |
|-----PCRpt, SYNC=0----->| (End of sync marker
| | LSP State Report
| | for PLSP-ID=0)
Figure 3: Successful state synchronization
The sequence where the PCE fails during the State Synchronization
phase is shown in Figure 4.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->|
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-----PCRpt, SYNC=1----->|
| |
|-PCRpt, SYNC=1 |
| \ ,-PCErr=?-|
| \ / |
| \/ |
| /\ |
| / `-------->| (Ignored)
|<--------` |
Figure 4: Failed state synchronization (PCE failure)
The sequence where the PCC fails during the State Synchronization
phase is shown in Figure 5.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->|
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-------- PCErr=? ------>|
| |
Figure 5: Failed state synchronization (PCC failure)
5.4.1. State Synchronization Avoidance
State Synchronization MAY be skipped following a PCEP session restart
if the state of both PCEP peers did not change during the period
prior to session re-initialization. To be able to make this
determination, state must be exchanged and maintained by both PCE and
PCC during normal operation. This is accomplished by keeping track
of the changes to the LSP State Database, using a database version
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called the LSP State Database Version.
The LSP State Database version is an unsigned 64-bit value that MUST
be incremented by 1 for each successive change in the LSP state
database. The LSP State Database version MUST start at 1 and may
wrap around. Values 0 and 0xFFFFFFFFFFFFFFFF are reserved. The PCC
is the owner of the LSP State Database version, which is incremented
each time a change is made to the PCC's local LSP State Database.
Operations that trigger a change to the local LSP State database
include a change in the LSP operational state, delegation of an LSP,
removal or addition of an LSP or change in any of the LSP attributes
that would trigger a report to the PCE. When State Synchronization
avoidance is enabled on a PCEP session, a PCC includes the LSP-DB-
VERSION TLV as an optional TLV in the LSP Object on each LSP State
Report. The LSP-DB-VERSION TLV contains a PCC's LSP State Database
version.
State Synchronization Avoidance is negotiated on a PCEP session
during session startup. To make sure that a PCEP peer can recognize
a previously connected peer even if its IP address changed, each PCEP
peer includes the PREDUNDANCY-GROUP-ID TLV in the OPEN message.
If both PCEP speakers set the INCLUDE-DB-VERSION Flag in the OPEN
object's STATEFUL-PCE-CAPABILITY TLV to 1, the PCC will include the
LSP-DB-VERSION TLV in each LSP Object. The TLV will contain the
PCC's latest LSP State Database version.
If a PCE's LSP State Database survived the restart of a PCEP session,
the PCE will include the LSP-DB-VERSION TLV in its OPEN object, and
the TLV will contain the last LSP State Database version received on
an LSP State Report from the PCC in a previous PCEP session. If a
PCC's LSP State Database survived the restart, the PCC will include
the LSP-DB-VERSION TLV in its OPEN object and the TLV will contain
the last LSP State Database version sent on an LSP State Report from
the PCC in the previous PCEP session. If a PCEP Speaker's LSP State
Database did not survive the restart of a PCEP session, the PCEP
Speaker MUST NOT include the LSP-DB-VERSION TLV in the OPEN Object.
If both PCEP Speakers include the LSP-DB-VERSION TLV in the OPEN
Object and the TLV values match, the PCC MAY skip State
Synchronization. Otherwise, the PCC MUST perform State
Synchronization. If the PCC attempts to skip State Synchronization
(i.e. the SYNC Flag = 0 on the first LSP State Report from the PCC),
the PCE MUST send back a PCError with Error-type 20 Error-value 2
'LSP Database version mismatch', and close the PCEP session.
If state synchronization is required, then prior to completing the
Initialization phase, the PCE MUST mark any LSPs in the LSP database
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that were previously reported by the PCC as stale. When the PCC
reports an LSP during state synchronization, if the LSP already
exists in the LSP database, the PCE MUST update the LSP database and
clear the stale marker from the LSP. When it has finished state
synchronization, the PCC MUST immediately send a PCRpt message
containing a state report with an LSP object containing an PLSP-ID of
0 and with the SYNC flag set to 0 (see Section 5.4). This state
report indicates to the PCE that state synchronization has completed.
On receiving this state report, the PCE MUST purge any LSPs from the
LSP database that are still marked as stale.
Note that a PCE MAY force State Synchronization by not including the
LSP-DB-VERSION TLV in its OPEN object.
Figure 6 shows an example sequence where State Synchronization is
skipped.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=42 \ ,---Open--|
| IDB=1 \ / DBv=42 |
| \/ IDB=1 |
| /\ |
| / `-------->| (OK to skip sync)
(Skip sync) |<--------` |
| . |
| . |
| . |
| |
|--PCRpt,DBv=43,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=44,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=45,SYNC=0-->|
| |
Figure 6: State Synchronization skipped
Figure 7 shows an example sequence where State Synchronization is
performed due to LSP State Database version mismatch during the PCEP
session setup. Note that the same State Synchronization sequence
would happen if either the PCC or the PCE would not include the LSP-
DB-VERSION TLV in their respective Open messages.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=46 \ ,---Open--|
| IDB=1 \ / DBv=42 |
| \/ IDB=1 |
| /\ |
| / `-------->| (Expect sync)
(Do sync) |<--------` | (Purge LSP State)
| |
|--PCRpt,DBv=46,SYNC=1-->| (Sync start)
| . |
| . |
| . |
|--PCRpt,DBv=46,SYNC=1-->| (Sync done)
| . |
| . |
| . |
|--PCRpt,DBv=47,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=48,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=49,SYNC=0-->|
| |
Figure 7: State Synchronization performed
Figure 8 shows an example sequence where State Synchronization is
skipped, but because one or both PCEP Speakers set the INCLUDE-DB-
VERSION Flag to 0, the PCC does not send LSP-DB-VERSION TLVs to the
PCE. If the current PCEP session restarts, the PCEP Speakers will
have to perform State Synchronization, since the PCE will not know
the PCC's latest LSP State Database version.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=42 \ ,---Open--|
| IDB=0 \ / DBv=42 |
| \/ IDB=0 |
| /\ |
| / `-------->| (OK to skip sync)
(Skip sync) |<--------` |
| . |
| . |
| . |
|------PCRpt,SYNC=0----->| (Regular
| | LSP State Report)
|------PCRpt,SYNC=0----->| (Regular
| | LSP State Report)
|------PCRpt,SYNC=0----->|
| |
Figure 8: State Synchronization skipped, no LSP-DB-VERSION TLVs sent
from PCC
5.4.2. PCE-triggered State Synchronization
Because the accuracy of the computations performed by the PCE is tied
to the accuracy of the view the PCE has on the state of the LSPs, it
can be beneficial to be able to resynchronize this state even after
the session has established. The PCE may use this approach to
continuously sanity check its state against the network, or to
recover from error conditions without having to tear down sessions.
To trigger a resynchronization with a PCC, the PCE MUST first mark
any LSPs in the LSP database that were previously reported by the PCC
as stale and then send a PCUpd for an LSP object containing a PLSP-ID
of 0 and with the SYNC flag set to 1. This PCUpd message is the
trigger for the PCC to enter the synchronization phase as described
in Section 5.4.1 and start sending PCRpt messages. After the receipt
of the end-of-synchronization marker, the PCE will purge LSPs which
were not refreshed.
5.5. LSP Delegation
If during Capability negotiation both the PCE and the PCC have
indicated that they support LSP Update, then the PCC may choose to
grant the PCE a temporary right to update (a subset of) LSP
attributes on one or more LSPs. This is called "LSP Delegation", and
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it MAY be performed at any time after the Initialization phase,
including during the State Synchronization phase.
LSP Delegation is controlled by operator-defined policies on a PCC.
LSPs are delegated individually - different LSPs may be delegated to
different PCEs. An LSP is delegated to at most one PCE at any given
point in time. The delegation policy, when all PCC's LSPs are
delegated to a single PCE at any given time, SHOULD be supported by
all delegation-capable PCCs. Conversely, the policy revoking the
delegation for all PCC's LSPs SHOULD also be supported
A PCE may return LSP delegation at any time if it no longer wishes to
update the LSP's state. A PCC may revoke LSP delegation at any time.
Delegation, Revocation, and Return are done individually for each
LSP.
In the event of an delegation being rejected or returned by a PCE,
the PCC should react based on local policy. It can, for example,
either retry delegating to the same PCE using an exponentially
increasing timer or delegate to an alternate PCE.
5.5.1. Delegating an LSP
A PCC delegates an LSP to a PCE by setting the Delegate flag in LSP
State Report to 1. If the PCE does not accept the LSP Delegation, it
MUST immediately respond with an empty LSP Update Request which has
the Delegate flag set to 0. If the PCE accepts the LSP Delegation,
it confirms this when it sends the first LSP Update Request for the
delegated LSP to the PCC by setting the Delegate flag to 1 (note that
this may occur at a later time).
The delegation sequence is shown in Figure 9.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->| LSP Delegated
| |
|---PCRpt, Delegate=1--->|
| . |
| . |
| . |
|<--(PCUpd,Delegate=1)---| Delegation confirmed
| |
|---PCRpt, Delegate=1--->|
| |
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Figure 9: Delegating an LSP
Note that for an LSP to remain delegated to a PCE, the PCC MUST set
the Delegate flag to 1 on each LSP Status Report sent to the PCE.
5.5.2. Revoking a Delegation
When a PCC decides that a PCE is no longer permitted to modify an
LSP, it revokes that LSP's delegation to the PCE. A PCC may revoke
an LSP delegation at any time during the LSP's life time. A PCC
revoking an LSP delegation MAY immediately clear the LSP state
provided by the PCE, but to avoid traffic loss, it SHOULD do so in a
make-before-break fashion. If the PCC has received but not yet acted
on PCUpd messages from the PCE for the LSP whose delegation is being
revoked, then it SHOULD ignore these PCUpd messages when processing
the message queue. All effects of all messages for which processing
started before the revocation took place MUST be allowed to complete
and the result MUST be given the same treatment as any LSP that had
been previously delegated to the PCE (e.g. the state MAY be
immediately cleared). Any further PCUpd messages from the PCE are
handled according to the PCUpd procedures described in this document.
If a PCEP session with the PCE to which the LSP is delegated exists
in the UP state during the revocation, the PCC MUST notify that PCE
by sending an LSP State Report with the Delegate flag set to 0, as
shown in Figure 10.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->|
| |
|<--(PCUpd,Delegate=1)---| Delegation confirmed
| . |
| . |
| . |
|---PCRpt, Delegate=0--->| PCC revokes delegation
| |
Figure 10: Revoking a Delegation
After an LSP delegation has been revoked, a PCE can no longer update
LSP's parameters; an attempt to update parameters of a non-delegated
LSP will result in the PCC sending a PCErr message indicating "LSP is
not delegated" (see Section 8.4).
When a PCC's PCEP session with a PCE terminates unexpectedly, the PCC
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MUST wait the time interval specified in Redelegation Timeout
Interval before revoking LSP delegations to that PCE and attempting
to redelegate LSPs to an alternate PCE. If a PCEP session with the
original PCE can be reestablished before the Redelegation Timeout
Interval timer expires, LSP delegations to the PCE remain intact.
Likewise, when a PCC's PCEP session with a PCE terminates
unexpectedly, the PCC MUST wait for the State Timeout Interval before
flushing any LSP state associated with that PCE. Note that the State
Timeout Interval timer may expire before the PCC has redelegated the
LSPs to another PCE, for example if a PCC is not connected to any
active stateful PCE or if no connected active stateful PCE accepts
the delegation. In this case, the PCC SHALL flush any LSP state set
by the PCE upon expiration of the State Timeout Interval and revert
to operator-defined default parameters. This operation SHOULD be
done in a make-before-break fashion.
The State Timeout Interval SHOULD be greater than or equal to the
Redelegation Timeout Interval and MAY be set to infinity (meaning
that until the PCC specifically takes action to change the parameters
set by the PCE, they will remain intact).
If State Synchronization Avoidance is enabled, a PCC MUST increment
its LSP State Database version when the 'Redelegation Timeout
Interval' timer expires.
5.5.3. Returning a Delegation
A PCE that no longer wishes to update an LSP's parameters SHOULD
return the LSP delegation back to the PCC by sending an empty LSP
Update Request which has the Delegate flag set to 0. Note that in
order to keep a delegation, the PCE MUST set the Delegate flag to 1
on each LSP Update Request sent to the PCC.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->| LSP delegated
| . |
| . |
| . |
|<--PCUpd, Delegate=0----| Delegation returned
| |
|---PCRpt, Delegate=0--->| No delegation for LSP
| |
Figure 11: Returning a Delegation
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If a PCC cannot delegate an LSP to a PCE (for example, if a PCC is
not connected to any active stateful PCE or if no connected active
stateful PCE accepts the delegation), the LSP delegation on the PCC
will time out within a configurable Redelegation Timeout Interval and
the PCC MUST flush any LSP state set by a PCE at the expiration of
the State Timeout Interval.
5.5.4. Redundant Stateful PCEs
Note that a PCE may not have any delegated LSPs: in a redundant
configuration where one PCE is backing up another PCE, the backup PCE
may have only a subset of LSPs delegated to it. The backup PCE does
not update any LSPs that are not delegated to it, but receives all
LSP State Reports from a PCC. When the primary PCE for a given LSP
set fails, after expiry of the Redelegation Timeout Interval, the PCC
SHOULD delegate to the redundant PCE all LSPs that had been
previously delegated to the failed PCE. Assuming that the State
Timeout Interval had been configured to be larger than the
Redelegation Timeout Interval (as recommended), this delegation
change will not cause any changes to the LSP parameters.
5.5.5. Redelegation on PCE failure
On failure, the goal is to: 1) avoid any traffic loss on the LSPs
that were updated by the PCE that crashed 2) minimize the churn in
the network in terms of ownership of the LSPs, 3) not leave any
"orphan" (undelegated) LSPs and 4) be able to control when the state
that was set by the PCE can be changed or purged. The values chosen
for the Redelegation Timeout and State Timeout values affect the
ability to accomplish these goals.
This section summarizes the behaviour with regards to LSP delegation
and LSP state on a PCE failure.
If the PCE crashses but recovers within the Redelegation Timeout,
both the delegation state and the LSP state are kept intact.
If the PCE crashes but does not recover within the Redelegation
Timeout, the delegation state is returned to the PCC. If the PCC can
redelegate the LSPs to another PCE, and that PCE accepts the
delegations, there will be no change in LSP state. If the PCC cannot
redelegate the LSPs to another PCE, then upon expiration of the State
Timeout Interval, the state set by the PCE is flushed, which may
cause change in the LSP state. Note that an operator may choose to
use an infinite State Timeout Interval if he wishes to maintain the
PCE state indefinetely. Note also that flushing the state should be
implemented using make-before-break to avoid traffic loss.
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If there is a hot-standby PCE, the Redelegation Timeout may be set to
0 through policy on the PCC, causing the LSPs to be redelegated
immediately to the PCC, which can delegate them immediately to the
hot-standby PCE. Assuming the State Timeout Interval is larger than
the Redelegation Timeout, the LSP state will be kept intact.
5.6. LSP Operations
5.6.1. Passive Stateful PCE Path Computation Request/Response
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
1) Path computation |----- PCReq message --->|
request sent to | |2) Path computation
PCE | | request received,
| | path computed
| |
|<---- PCRep message ----|3) Computed paths
| (Positive reply) | sent to the PCC
| (Negative reply) |
4) LSP Status change| |
event | |
| |
5) LSP Status Report|----- PCRpt message --->|
sent to all | . |
stateful PCEs | . |
| . |
6) Repeat for each |----- PCRpt message --->|
LSP status change| |
| |
Figure 12: Passive Stateful PCE Path Computation Request/Response
Once a PCC has successfully established a PCEP session with a passive
stateful PCE and the PCC's LSP state is synchronized with the PCE
(i.e. the PCE knows about all PCC's existing LSPs), if an event is
triggered that requires the computation of a set of paths, the PCC
sends a path computation request to the PCE ([RFC5440], Section
4.2.3). The PCReq message MAY contain the LSP Object to identify the
LSP for which the path computation is requested.
Upon receiving a path computation request from a PCC, the PCE
triggers a path computation and returns either a positive or a
negative reply to the PCC ([RFC5440], Section 4.2.4).
Upon receiving a positive path computation reply, the PCC receives a
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set of computed paths and starts to setup the LSPs. For each LSP, it
sends an LSP State Report carried on a PCRpt message to the PCE,
indicating that the LSP's status is 'Pending'.
Once an LSP is up, the PCC sends an LSP State Report carried on a
PCRpt message to the PCE, indicating that the LSP's status is 'Up'.
If the LSP could not be set up, the PCC sends an LSP State Report
indicating that the LSP is "Down' and stating the cause of the
failure. Note that due to timing constraints, the LSP status may
change from 'Pending' to 'Up' (or 'Down') before the PCC has had a
chance to send an LSP State Report indicating that the status is
'Pending'. In such cases, the PCC may choose to only send the PCRpt
indicating the latest status ('Up' or 'Down').
Upon receiving a negative reply from a PCE, a PCC may decide to
resend a modified request or take any other appropriate action. For
each requested LSP, it also sends an LSP State Report carried on a
PCRpt message to the PCE, indicating that the LSP's status is 'Down'.
There is no direct correlation between PCRep and PCRpt messages. For
a given LSP, multiple LSP State Reports will follow a single PC
Reply, as a PCC notifies a PCE of the LSP's state changes.
A PCC sends each LSP State Report to each stateful PCE that is
connected to the PCC.
Note that a single PCRpt message MAY contain multiple LSP State
Reports.
The passive stateful PCE is the model for stateful PCEs is described
in [RFC4655], Section 6.8.
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5.6.2. Active Stateful PCE LSP Update
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
1) LSP State |-- PCRpt, Delegate=1 -->|
Synchronization | . |
or add new LSP | . |2) PCE decides to
| . | update the LSP
| |
|<---- PCUpd message ----|3) PCUpd message sent
| | to PCC
| |
| |
4) LSP Status Report|---- PCRpt message ---->|
sent(->Pending) | . |
| . |
| . |
5) LSP Status Report|---- PCRpt message ---->|
sent (->Up|Down) | |
| |
Figure 13: Active Stateful PCE
Once a PCC has successfully established a PCEP session with an active
stateful PCE, the PCC's LSP state is synchronized with the PCE (i.e.
the PCE knows about all PCC's existing LSPs) and LSPs have been
delegated to the PCE, the PCE can modify LSP parameters of delegated
LSPs.
A PCE sends an LSP Update Request carried on a PCUpd message to the
PCC. The LSP Update Request contains a variety of objects that
specify the set of constraints and attributes for the LSP's path.
Each LSP Update Request has a unique identifier, the SRP-ID-number,
carried in the SRP (Stateful PCE Request Parameters) Object described
in Section 7.2. The SRP-ID-number is used to correlate errors and
state reports to LSP Update Requests. A single PCUpd message MAY
contain multiple LSP Update Requests.
Upon receiving a PCUpd message the PCC starts to setup LSPs specified
in LSP Update Requests carried in the message. For each LSP, it
sends an LSP State Report carried on a PCRpt message to the PCE,
indicating that the LSP's status is 'Pending'. If the PCC decides
that the LSP parameters proposed in the PCUpd message are
unacceptable, it MUST report this error by including the LSP-ERROR-
CODE TLV (Section 7.3.3) with LSP error value="Unacceptable PCUpd
parameters" in the LSP object in the PCRpt message to the PCE. Based
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on local policy, it MAY react further to this error by revoking the
delegation. If the PCC receives a PCUpd message for an LSP object
identified with a PLSP-ID that does not exist on the PCC, it MUST
generate a PCErr with error type 19, error value 3, "Unknown PLSP-ID"
(see Section 8.4).
Once an LSP is up, the PCC sends an LSP State Report (PCRpt message)
to the PCE, indicating that the LSP's status is 'Up'. If the LSP
could not be set up, the PCC sends an LSP State Report indicating
that the LSP is 'Down' and stating the cause of the failure. A PCC
may choose to compress LSP State Reports to only reflect the most up
to date state, as discussed in the previous section.
A PCC sends each LSP State Report to each stateful PCE that is
connected to the PCC.
PCErr and PCRpt messages triggered as a result of a PCUpd message
MUST include the SRP-ID-number from the PCUpd. This provides
correlation of requests and errors and acknowledgement of state
processing. The PCC may choose to compress state when processing
PCUpd. In this case, receipt of a higher SRP-ID-number implicitly
acknowledges processing all the earlier updates for the specific LSP.
A PCC MUST NOT send to any PCE a Path Computation Request for a
delegated LSP. Should the PCC decide it wants to issue a Path
Computation Request on a delegated LSP, it MUST perform Delegation
Revocation procedure first.
5.7. LSP Protection
LSP protection and interaction with stateful PCE, as well as the
extensions necessary to implement this functionality will be
discussed in a separate draft.
5.8. Transport
A Permanent PCEP session MUST be established between a stateful PCE
and the PCC. In the case of session failure, session reestablishment
MUST be re-attempted per the procedures defined in [RFC5440].
6. PCEP Messages
As defined in [RFC5440], a PCEP message consists of a common header
followed by a variable-length body made of a set of objects that can
be either mandatory or optional. An object is said to be mandatory
in a PCEP message when the object must be included for the message to
be considered valid. For each PCEP message type, a set of rules is
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defined that specify the set of objects that the message can carry.
An implementation MUST form the PCEP messages using the object
ordering specified in this document.
6.1. The PCRpt Message
A Path Computation LSP State Report message (also referred to as
PCRpt message) is a PCEP message sent by a PCC to a PCE to report the
current state of an LSP. A PCRpt message can carry more than one LSP
State Reports. A PCC can send an LSP State Report either in response
to an LSP Update Request from a PCE, or asynchronously when the state
of an LSP changes. The Message-Type field of the PCEP common header
for the PCRpt message is set to [TBD].
The format of the PCRpt message is as follows:
<PCRpt Message> ::= <Common Header>
<state-report-list>
Where:
<state-report-list> ::= <state-report>[<state-report-list>]
<state-report> ::= <SRP>
<LSP>
<path>
Where:
<path> is defined in [RFC5440] and extended by PCEP extensions.
The SRP object (see Section 7.2) is mandatory, and it MUST be
included for each LSP State Report in the PCRpt message. The value
of the SRP-ID-number in the SRP Object MUST be the same as that sent
in the PCUpd message that triggered the state that is reported, or
the reserved value 0x00000000 if the state is not as a result of
processing a PCUpd message. If the PCC compressed several PCUpd
messages for the same LSP by only processing the latest one, then it
should use the SRP-ID-number of that request. If the SRP object is
missing, the receiving PCE MUST send a PCErr message with Error-
type=6 (Mandatory Object missing) and Error-value=[TBD] (SRP object
missing). No state compression is allowed for state reporting. The
PCC MUST explicitly report state changes (including removal) for
paths it manages.
The LSP object (see Section 7.3) is mandatory, and it MUST be
included in each LSP State Report on the PCRpt message. If the LSP
object is missing, the receiving PCE MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=[TBD] (LSP
object missing).
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If the LSP transitioned to non-operational state, the PCC SHOULD
include the LSP-ERROR-TLV (Section 7.3.3) with the relevant LSP Error
Code to report the error to the PCE.
6.2. The PCUpd Message
A Path Computation LSP Update Request message (also referred to as
PCUpd message) is a PCEP message sent by a PCE to a PCC to update
attributes of an LSP. A PCUpd message can carry more than one LSP
Update Request. The Message-Type field of the PCEP common header for
the PCUpd message is set to [TBD].
The format of a PCUpd message is as follows:
<PCUpd Message> ::= <Common Header>
<udpate-request-list>
Where:
<update-request-list> ::= <update-request>[<update-request-list>]
<update-request> ::= <SRP>
<LSP>
<path>
Where:
<path>::= <ERO><attribute-list>
Where:
<attribute-list> is defined in [RFC5440] and extended by PCEP extensions.
There are three mandatory objects that MUST be included within each
LSP Update Request in the PCUpd message: the SRP Object (see
Section 7.2), the LSP object (see Section 7.3) and the ERO object (as
defined in [RFC5440]. If the SRP object is missing, the receiving
PCC MUST send a PCErr message with Error-type=6 (Mandatory Object
missing) and Error-value=[TBD] (SRP object missing). If the LSP
object is missing, the receiving PCC MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=[TBD] (LSP
object missing). If the ERO object is missing, the receiving PCC
MUST send a PCErr message with Error-type=6 (Mandatory Object
missing) and Error-value=[TBD] (ERO object missing).
A PCC only acts on an LSP Update Request if permitted by the local
policy configured by the network manager. Each LSP Update Request
that the PCC acts on results in an LSP setup operation. An LSP
Update Request MUST contain all LSP parameters that a PCE wishes to
set for the LSP. A PCC MAY set missing parameters from locally
configured defaults. If the LSP specified in the Update Request is
already up, it will be re-signaled.
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The PCC SHOULD use the make-before-break procedures described in
[RFC3209] in the re-signaling operation. During this process, two
paths will briefly co-exist. The PCC MUST send separate PCRpt
messages for each, identified by the LSP-IDENTIFIERS TLV. When the
old path is torn down after the head end switches over the traffic,
this event MUST be reported by sending a PCRpt message with the LSP-
IDENTIFIERS-TLV or the old path, and the R bit set. Thus, a make-
before-break operation will typically result in at least two PCRpt
messages, one for the new path and one for the removal of the old
path (more messages may be possible if intermediate states are
reported).
A PCC MUST respond with an LSP State Report to each LSP Update
Request it processed to indicate the resulting state of the LSP in
the network (even if this processing did not result in changing the
state of the LSP). The SRP-ID-number included in the PCRpt MUST
match that in the PCUpd. A PCC MAY respond with multiple LSP State
Reports to report LSP setup progress of a single LSP. In that case,
the SRP-ID-number MUST be included while the state of the LSP is
"pending", afterwards the reserved value 0x00000000 SHOULD be used..
Note that a PCC MUST process all LSP Update Requests - for example,
an LSP Update Request is sent when a PCE returns delegation or puts
an LSP into non-operational state. The protocol relies on TCP for
message-level flow control.
If the rate of PCUpd messages sent to a PCC for the same target LSP
exceeds the rate at which the PCC can signal LSPs into the network,
the PCC MAY perform state compression and only signal the last
modification in its queue, as the last PCUpd contains the most up-to-
date desired state for the LSP. If two PCUpd arrive for the same LSP
in quick succession and the PCC started the signaling of the changes
relevant to the first PCUpd, then it MUST wait until the signaling
finishes (and report the new state via a PCRpt) before attempting to
apply the changes indicated in the second PCUpd.
Note also that it is up to the PCE to handle inter-LSP dependencies;
for example, if ordering of LSP set-ups is required, the PCE has to
wait for an LSP State Report for a previous LSP before starting the
update of the next LSP. If the PCUpd cannot be satisfied (for
example due to unsupported object or TLV), the PCC MUST respond with
an PCErr message
6.3. The PCErr Message
If the stateful PCE capability has been negotiated on the PCEP
session, the PCErr message MUST include the SRP object. If the error
reported is the result of an LSP update request, then the SRP-ID-
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number MUST be the one from the PCUpd that triggered the error. If
it is unsolicited, the SRP-ID-number MUST be the reserved value
0x00000000.
6.4. The PCReq Message
A PCC MAY include the LSP object in the PCReq message (see
Section 7.3) if the stateful PCE capability has been negotiated on a
PCEP session between the PCC and a PCE.
The definition of the PCReq message from [RFC5440] and
[I-D.ietf-pce-gmpls-pcep-extensions] is extended to optionally
include the LSP object after the END-POINTS object. For illustration
purposes, the encoding from [RFC5440] will become:
<PCReq Message>::= <Common Header>
[<svec-list>]
<request-list>
Where:
<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSP>] <--- New Object
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
6.5. The PCRep Message
A PCE MAY include the LSP object in the PCRep message (see
(Section 7.3) if the stateful PCE capability has been negotiated on a
PCEP session between the PCC and the PCE and the LSP object was
included in the corresponding PCReq message from the PCC.
The definition of the PCRep message from [RFC5440] and
[I-D.ietf-pce-gmpls-pcep-extensions] is extended to optionally
include the LSP object after the RP object. For illustration
purposes, the encoding from [RFC5440] will become:
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<PCRep Message> ::= <Common Header>
<response-list>
Where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<LSP>] <--- New Object
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
7. Object Formats
The PCEP objects defined in this document are compliant with the PCEP
object format defined in [RFC5440]. The P flag and the I flag of the
PCEP objects defined in this document MUST always be set to 0 on
transmission and MUST be ignored on receipt since these flags are
exclusively related to path computation requests.
7.1. OPEN Object
This document defines two new optional TLVs for use in the OPEN
Object.
7.1.1. Stateful PCE Capability TLV
The STATEFUL-PCE-CAPABILITY TLV is an optional TLV for use in the
OPEN Object for stateful PCE capability negotiation. Its format is
shown in the following figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |S|U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: STATEFUL-PCE-CAPABILITY TLV format
The type of the TLV is [TBD] and it has a fixed length of 4 octets.
The value comprises a single field - Flags (32 bits):
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U (LSP-UPDATE-CAPABILITY - 1 bit): if set to 1 by a PCC, the U Flag
indicates that the PCC allows modification of LSP parameters; if
set to 1 by a PCE, the U Flag indicates that the PCE is capable of
updating LSP parameters. The LSP-UPDATE-CAPABILITY Flag must be
advertised by both a PCC and a PCE for PCUpd messages to be
allowed on a PCEP session.
S (INCLUDE-DB-VERSION - 1 bit): if set to 1 by both PCEP Speakers,
the PCC will include the LSP-DB-VERSION TLV in each LSP Object.
Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
Negotiation of the stateful PCE capability implies support of LSPs
that are signaled via RSVP, as well as the objects, TLVs and
procedures defined in this document.
7.1.2. LSP State Database Version TLV
LSP-DB-VERSION is an optional TLV that MAY be included in the OPEN
Object when a PCEP Speaker wishes to determine if State
Synchronization can be skipped when a PCEP session is restarted. If
sent from a PCE, the TLV contains the local LSP State Database
version from the last valid LSP State Report received from a PCC. If
sent from a PCC, the TLV contains the PCC's local LSP State Database
version, which is incremented each time the LSP State Database is
updated.
The format of the LSP-DB-VERSION TLV is shown in the following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP State DB Version |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: LSP-DB-VERSION TLV format
The type of the TLV is [TBD] and it has a fixed length of 8 octets.
The value contains a 64-bit unsigned integer.
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7.1.3. PCE Redundancy Group Identifier TLV
PREDUNDANCY-GROUP-ID is an optional TLV that MAY be included in the
OPEN Object when a PCEP Speaker wishes to determine if State
Synchronization can be skipped when a PCEP session is restarted. It
contains a unique identifier for the node that does not change during
the life time of the PCEP Speaker. It identifies the PCEP Speaker to
its peers if the Speaker's IP address changed.
The format of the PREDUNDANCY-GROUP-ID TLV is shown in the following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// PCE redundancy group Identifier //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: PREDUNDANCY-GROUP-ID TLV format
The type of the TLV is [TBD] and it has a a variable length, which
MUST be greater than 0. The value contains a node identifier that
MUST be unique in the network. The node identifier MAY be configured
by an operator. If the node identifier is not configured by the
operator, it can be derived from a PCC's MAC address or serial
number.
7.2. SRP Object
The SRP (Stateful PCE Request Parameters) object MUST be carried
within each PCUpd and PCRpt message and MAY be carried within PCNtf
and PCEerr messages. The SRP object is used to correlate between
update requests sent by the PCE and the error reports and state
reports sent by the PCC. The P flag in the common object header of
the SRP object MUST be set to 0.
SRP Object-Class is [TBD].
SRP Object-Type is 1.
The format of the SRP object body is shown in Figure 17:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRP-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: The SRP Object format
The SRP object body has a variable length and may contain additional
TLVs. The SYMBOLIC-PATH-NAME TLV MAY be included as one of the
optional TLVs.
Flags (32 bits): None defined yet.
SRP-ID-number (32 bits): The SRP-ID-number value combined with the
source IP address of the PCC and the PCE uniquely identify the
operation that the PCE has requested the PCC to perform on a given
LSP. The SRP-ID-number is incremented each time a new request is
sent to the PCC, and may wrap around.
The values 0x00000000 and 0xFFFFFFFF are reserved.
Every request to update an LSP receives a new SRP-ID-number. This
number is unique per PCEP session and is incremented each time an
operation is requested from the PCE. Thus, for a given LSP there may
be more than one SRP-id-number unacknowledged at a given time. The
value of the SRP-ID-number is echoed back by the PCC in PCErr and
PCRpt messages to allow for correlation between requests made by the
PCE and errors or state reports generated by the PCC. If the error
or report were not as a result of a PCE operation (for example in the
case of a link down event), then the reserved value of 0x00000000 is
used instead. An SRP-ID-number is considered unacknowledged and
cannot be reused until a PCErr or PCRpt arrives with an SRP-ID-number
equal or higher for the same LSP. A PCRpt with state "Pending" is
not considered as an acknowledgement.
7.3. LSP Object
The LSP object MUST be present within PCRpt and PCUpd messages. The
LSP object MAY be carried within PCReq and PCRep messages if the
stateful PCE capability has been negotiated on the session. The LSP
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object contains a set of fields used to specify the target LSP, the
operation to be performed on the LSP, and LSP Delegation. It also
contains a flag indicating to a PCE that the LSP state
synchronization is in progress. This document focuses on LSPs that
are signaled with RSVP, many of the TLVs used with the LSP object
mirror RSVP state.
LSP Object-Class is [TBD].
LSP Object-Type is 1.
The format of the LSP object body is shown in Figure 18:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PLSP-ID | Flags | O|A|R|S|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | LSP-sig-type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: The LSP Object format
PLSP-ID (20 bits): An identifier for the LSP. A PCC creates a unique
PLSP-ID for each LSP that is constant for the life time of a PCEP
session. The mapping of the Symbolic Path Name to PLSP-ID is
communicated to the PCE by sending a PCRpt message containing the
SYMBOLIC-PATH-NAME TLV. All subsequent PCEP messages then address
the LSP by the PLSP-ID. The values of 0 and 0xFFFFF are reserved.
Note that the PLSP-ID is a value that is constant for the life time
of the PCEP session, during which time for an RSVP-signaled LSP there
might be a different RSVP identifiers (LSP-id, tunnel-id) allocated
it.
Flags (12 bits):
D (Delegate - 1 bit): on a PCRpt message, the D Flag set to 1
indicates that the PCC is delegating the LSP to the PCE. On a
PCUpd message, the D flag set to 1 indicates that the PCE is
confirming the LSP Delegation. To keep an LSP delegated to the
PCE, the PCC must set the D flag to 1 on each PCRpt message for
the duration of the delegation - the first PCRpt with the D flag
set to 0 revokes the delegation. To keep the delegation, the PCE
must set the D flag to 1 on each PCUpd message for the duration of
the delegation - the first PCUpd with the D flag set to 0 returns
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the delegation.
S (SYNC - 1 bit): the S Flag MUST be set to 1 on each LSP State
Report sent from a PCC during State Synchronization. The S Flag
MUST be set to 0 otherwise.
R(Remove - 1 bit): On PCRpt messages the R Flag indicates that the
LSP has been removed from the PCC and the PCE SHOULD remove all
state from its database. Upon receiving an LSP State Report with
the R Flag set to 1 for an RSVP-signaled LSP, the PCE SHOULD
remove all state for the path identified by the LSP Identifiers
TLV from its database. When the all-zeros LSP-IDENTIFIERS-TLV is
used, the PCE SHOULD remove all state for the PLSP-ID from its
database.
A(Administrative - 1 bit): On PCRpt messages, the A Flag indicates
the PCC's target operational status for this LSP. On PCUpd
messages, the A Flag indicates the LSP status that the PCE desires
for this LSP. In both cases, a value of '1' means that the
desired operational state is active, and a value of '0' means that
the desired operational state is inactive. A PCC ignores the A
flag on a PCUpd message unless the operator's policy allows the
PCE to control the corresponding LSP's administrative state.
O(Operational - 3 bits): On PCRpt messages, the O Field represents
the operational status of the LSP.
The following values are defined:
0 - DOWN: not active.
1 - UP: signalled.
2 - ACTIVE: up and carrying traffic.
3 - GOING-DOWN: LSP is being torn down, resources are being
released.
4 - GOING-UP: LSP is being signalled.
5-7 - Reserved: these values MUST be set to 0 on transmission and
MUST be ignored on receipt.
Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
LSP-sig-type (8 bits) - identifies the method used for signaling the
LSP. If a PCEP speaker receives an LSP object with LSP-sig-type that
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had not been previously negotiated, a PCErr with error type 19, error
value 5, "Unsupported LSP signaling type", (see Section 8.4) MUST be
sent. If there is a mismatch in the LSP signaling type for a
particular LSP between the PCEP speakers, a PCErr with error type 19,
error value 4, "Mismatched LSP signaling type" (see Section 8.4) MUST
be sent by the party identifying the mismatch.
Optional TLVs that may be included in the LSP Object are described in
the following sections.
7.3.1. LSP Identifiers TLVs
The LSP Identifiers TLV MUST be included in the LSP object in PCRpt
messages for RSVP-signaled LSPs. If the TLV is missing, the PCE will
generate an error with error-type 6 (mandatory object missing) and
Error Value 11 (LSP-IDENTIFIERS TLV missing) and close the session.
The LSP Identifiers TLV MAY be included in the LSP object in PCUpd
messages for RSVP-signaled LSPs. The special value of all zeros for
this TLV is used to refer to all paths pertaining to a particular
PLSP-ID. There are two LSP Identifiers TLVs, one for IPv4 and one
for IPv6.
It is the responsibility of the PCC to send to the PCE the
identifiers for each RSVP incarnation of the tunnel. For exmple, in
a make-before-break scenario, the PCC MUST send a separate PCRpt for
the old and for the reoptimized paths, and explicitly report removal
of any of these paths using the R bit in the LSP object.
The format of the IPV4-LSP-IDENTIFIERS TLV is shown in the following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Tunnel Sender Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP ID | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: IPV4-LSP-IDENTIFIERS TLV format
The type of the TLV is [TBD] and it has a fixed length of 12 octets.
The value contains the following fields:
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IPv4 Tunnel Sender Address: contains the sender node's IPv4 address,
as defined in [RFC3209], Section 4.6.2.1 for the LSP_TUNNEL_IPv4
Sender Template Object.
LSP ID: contains the 16-bit 'LSP ID' identifier defined in
[RFC3209], Section 4.6.2.1 for the LSP_TUNNEL_IPv4 Sender Template
Object.
Tunnel ID: contains the 16-bit 'Tunnel ID' identifier defined in
[RFC3209], Section 4.6.1.1 for the LSP_TUNNEL_IPv4 Session Object.
Tunnel ID remains constant over the life time of a tunnel.
Extended Tunnel ID: contains the 32-bit 'Extended Tunnel ID'
identifier defined in [RFC3209], Section 4.6.1.1 for the
LSP_TUNNEL_IPv4 Session Object.
The format of the IPV6-LSP-IDENTIFIERS TLV is shown in l following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=36 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| IPv6 tunnel sender address |
+ (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP ID | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Extended Tunnel ID |
+ (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: IPV6-LSP-IDENTIFIERS TLV format
The type of the TLV is [TBD] and it has a fixed length of 36 octets.
The value contains the following fields:
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IPv6 Tunnel Sender Address: contains the sender node's IPv6 address,
as defined in [RFC3209], Section 4.6.2.2 for the LSP_TUNNEL_IPv6
Sender Template Object.
LSP ID: contains the 16-bit 'LSP ID' identifier defined in
[RFC3209], Section 4.6.2.2 for the LSP_TUNNEL_IPv6 Sender Template
Object.
Tunnel ID: contains the 16-bit 'Tunnel ID' identifier defined in
[RFC3209], Section 4.6.1.2 for the LSP_TUNNEL_IPv6 Session Object.
Tunnel ID remains constant over the life time of a tunnel.
However, when Global Path Protection or Global Default Restoration
is used, both the primary and secondary LSPs have their own Tunnel
IDs. A PCC will report a change in Tunnel ID when traffic
switches over from primary LSP to secondary LSP (or vice versa).
Extended Tunnel ID: contains the 128-bit 'Extended Tunnel ID'
identifier defined in [RFC3209], Section 4.6.1.2 for the
LSP_TUNNEL_IPv6 Session Object.
7.3.2. Symbolic Path Name TLV
Each LSP (path) MUST have a symbolic name that is unique in the PCC.
This symbolic path name MUST remain constant throughout a path's
lifetime, which may span across multiple consecutive PCEP sessions
and/or PCC restarts. The symbolic path name MAY be specified by an
operator in a PCC's configuration. If the operator does not specify
a unique symbolic name for a path, the PCC MUST auto-generate one.
The SYMBOLIC-PATH-NAME TLV MUST be included in the LSP State Report
when during a given PCEP session an LSP is first reported to a PCE.
A PCC sends to a PCE the first LSP State Report either during State
Synchronization, or when a new LSP is configured at the PCC. The
symbolic path name MAY be included in subsequent LSP State Reports
for the LSP.
The SYMBOLIC-PATH-NAME TLV MAY appear as a TLV in both the LSP Object
and the LSPA Object.
The format of the SYMBOLIC-PATH-NAME TLV is shown in the following
figure:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Symbolic Path Name //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: SYMBOLIC-PATH-NAME TLV format
The type of the TLV is [TBD] and it has a variable length, which MUST
be greater than 0.
7.3.3. LSP Error Code TLV
The LSP Error code TLV is an optional TLV for use in the LSP object
to convey error information. When an LSP Update Request fails, an
LSP State Report MUST be sent to report the current state of the LSP,
and SHOULD contain the LSP-ERROR-CODE TLV indicating the reason for
the failure. Similarly, when a PCRpt is sent as a result of an LSP
transitioning to non-operational state, the LSP-ERROR-CODE TLV SHOULD
be included to indicate the reason for the transition.
The format of the LSP-ERROR-CODE TLV is shown in the following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: LSP-ERROR-CODE TLV format
The type of the TLV is [TBD] and it has a fixed length of 4 octets.
The value contains an error code that indicates the cause of the
failure.
The following LSP Error Codes are defined:
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Value Meaning
1 Unknown reason
2 Limit reached for PCE-controlled LSPs
3 Too many pending LSP update requests
4 Unacceptable PCUpd parameters
5 Internal error
6 LSP administratively brought down
7 LSP preempted
8 RSVP signaling error
7.3.4. RSVP Error Spec TLV
The RSVP-ERROR-SPEC TLV is an optional TLV for use in the LSP object
to carry RSVP error information. It includes the RSVP ERROR_SPEC or
USER_ERROR_SPEC Object ([RFC2205] and [RFC5284]) which were returned
to the PCC from a downstream node. If the set up of an LSP fails at
a downstream node which returned an ERROR_SPEC to the PCC, the PCC
SHOULD include in the PCRpt for this LSP the LSP-ERROR-CODE TLV with
LSP Error Code = "RSVP signaling error" and the RSVP-ERROR-SPEC TLV
with the relevant RSVP ERROR-SPEC or USER_ERROR_SPEC Object.
The format of the RSVP-ERROR-SPEC TLV is shown in the following
figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ RSVP ERROR_SPEC or USER_ERROR_SPEC Object +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: RSVP-ERROR-SPEC TLV format
The type of the TLV is [TBD] and it has a variable length. The value
contains the RSVP ERROR_SPEC or USER_ERROR_SPEC object, including the
object header.
7.3.5. LSP State Database Version TLV
The LSP-DB-VERSION TLV can be included as an optional TLV in the LSP
object. The LSP-DB-VERSION TLV is discussed in Section 5.4.1 which
covers state synchronization avoidance. The format of the TLV is
described in Section 7.1.2, where the details of its use in the OPEN
message are listed.
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If State Synchronization Avoidance has been enabled on a PCEP session
(as described in Section 5.4.1) , a PCC MUST include the LSP-DB-
VERSION TLV in each LSP Object sent out on the session. If the TLV
is missing, the PCE will generate an error with error-type 6
(mandatory object missing) and Error Value 12 (LSP-DB-VERSION TLV
missing) and close the session. If State Synchronization Avoidance
has not been enabled on a PCEP session, the PCC SHOULD NOT include
the LSP-DB-VERSION TLV in the LSP Object and the PCE SHOULD ignore it
were it to receive one.
Since a PCE does not send LSP updates to a PCC, a PCC should never
encounter this TLV. A PCC SHOULD ignore the LSP-DB-VERSION TLV, were
it to receive one from a PCE.
7.3.6. Delegation Parameters TLVs
Multiple delegation parameters, such as sub-delegation permissions,
authentication parameters, etc. need to be communicated from a PCC to
a PCE during the delegation operation. Delegation parameters will be
carried in multiple delegation parameter TLVs, which will be defined
in future revisions of this document.
7.4. Optional TLVs for the LSPA Object
TLVs that may be included in the LSPA Object are described in the
following sections and in separate technology-specific documents.
7.4.1. Symbolic Path Name TLV
See section Section 7.3.2.
8. IANA Considerations
This document requests IANA actions to allocate code points for the
protocol elements defined in this document. Values shown here are
suggested for use by IANA.
8.1. PCEP Messages
This document defines the following new PCEP messages:
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Value Meaning Reference
10 Report This document
11 Update This document
8.2. PCEP Objects
This document defines the following new PCEP Object-classes and
Object-values:
Object-Class Value Name Reference
32 LSP This document
Object-Type
1
33 SRP This document
Object-Type
1
8.3. LSP Object
This document requests that a registry is created to manage the Flags
field of the LSP object. New values are to be assigned by Standards
Action [RFC5226]. Each bit should be tracked with the following
qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
The following values are defined in this document:
Bit Description Reference
25-27 Operational (3 bits) This document
28 Administrative This document
29 Remove This document
30 SYNC This document
31 Delegate This document
8.4. PCEP-Error Object
This document defines new Error-Type and Error-Value for the
following new error conditions:
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Error-Type Meaning
6 Mandatory Object missing
Error-value=8: LSP Object missing
Error-value=9: ERO Object missing
Error-value=10: SRP Object missing
Error-value=11: LSP-IDENTIFIERS TLV missing
Error-value=12: LSP-DB-VERSION TLV missing
19 Invalid Operation
Error-value=1: Attempted LSP Update Request for a non-
delegated LSP. The PCEP-ERROR Object
is followed by the LSP Object that
identifies the LSP.
Error-value=2: Attempted LSP Update Request if active
stateful PCE capability was not
negotiated active PCE.
Error-value=3: Attempted LSP Update Request for an LSP
identified by an unknown PLSP-ID.
Error-value=4: Mismatched LSP signaling type.
Error-value=5: Unsupported LSP signaling type.
20 LSP State synchronization error.
Error-value=1: A PCE indicates to a PCC that it can
not process (an otherwise valid) LSP
State Report. The PCEP-ERROR Object is
followed by the LSP Object that
identifies the LSP.
Error-value=2: LSP Database version mismatch.
Error-value=3: The LSP-DB-VERSION TLV Missing when
State Synchronization Avoidance
enabled.
8.5. PCEP TLV Type Indicators
This document defines the following new PCEP TLVs:
Value Meaning Reference
16 STATEFUL-PCE-CAPABILITY This document
17 SYMBOLIC-PATH-NAME This document
18 IPV4-LSP-IDENTIFIERS This document
19 IPV6-LSP-IDENTIFIERS This document
20 LSP-ERROR-CODE This document
21 RSVP-ERROR-SPEC This document
23 LSP-DB-VERSION This document
24 PREDUNDANCY-GROUP-ID This document
25 TUNNEL-ID This document
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8.6. STATEFUL-PCE-CAPABILITY TLV
This document requests that a registry is created to manage the Flags
field in the STATEFUL-PCE-CAPABILITY TLV in the OPEN object. New
values are to be assigned by Standards Action [RFC5226]. Each bit
should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
The following values are defined in this document:
Bit Description Reference
30 INCLUDE-DB-VERSION This document
31 LSP-UPDATE-CAPABILITY This document
8.7. LSP-ERROR-CODE TLV
This document requests that a registry is created to manage the value
of the LSP error code field in this TLV. This field specifies the
reason for failure to update the LSP.
Value Meaning
1 Unknown reason
2 Limit reached for PCE-controlled LSPs
3 Too many pending LSP update requests
4 Unacceptable PCUpd parameters
5 Internal error
6 LSP administratively brought down
7 LSP preempted
8 RSVP signaling error
8.8. LSP-SIG-TYPE field in the LSP object
This document requests that a registry is created to manage the value
of the LSP type field in the LSP object, which defines the technology
used for LSP setup.
Value Meaning
0 RSVP
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9. Manageability Considerations
All manageability requirements and considerations listed in [RFC5440]
apply to PCEP protocol extensions defined in this document. In
addition, requirements and considerations listed in this section
apply.
9.1. Control Function and Policy
In addition to configuring specific PCEP session parameters, as
specified in [RFC5440], Section 8.1, a PCE or PCC implementation MUST
allow configuring the stateful PCEP capability and the LSP Update
capability. A PCC implementation SHOULD allow the operator to
specify multiple candidate PCEs for and a delegation preference for
each candidate PCE. A PCC SHOULD allow the operator to specify an
LSP delegation policy where LSPs are delegated to the most-preferred
online PCE. A PCC MAY allow the operator to specify different LSP
delegation policies.
A PCE or PCC implementation SHOULD allow the operator to configure a
PREDUNDANCY-GROUP-ID (Section 7.1.3).
A PCC implementation which allows concurrent connections to multiple
PCEs SHOULD allow the operator to group the PCEs by administrative
domains and it MUST NOT advertise LSP existence and state to a PCE if
the LSP is delegated to a PCE in a different group.
A PCC implementation SHOULD allow the operator to specify whether the
PCC will advertise LSP existence and state for LSPs that are not
controlled by any PCE (for example, LSPs that are statically
configured at the PCC).
A PCC implementation SHOULD allow the operator to specify both the
Redelegation Timeout Interval and the State Timeout Interval. The
default value of the Redelegation Timeout Interval SHOULD be set to
30 seconds. An operator MAY also configure a policy that will
dynamically adjust the Redelegation Timeout Interval, for example
setting it to zero when the PCC has an established session to a
backup PCE. The default value for the State Timeout Interval SHOULD
be set to 60 seconds.
After the expiration of the State Timeout Interval, the LSP reverts
to operator-defined default parameters. A PCC implementation MUST
allow the operator to specify the default LSP parameters. To achieve
a behavior where the LSP retains the parameters set by the PCE until
such time that the PCC makes a change to them, a State Timeout
Interval of infinity SHOULD be used. Any changes to LSP parameters
SHOULD be done in make-before-break fashion.
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A PCC implementation SHOULD allow the operator to specify delegation
priority for PCEs. This effectively defines the primary PCE and one
or more backup PCEs to which primary PCE's LSPs can be delegated when
the primary PCE fails.
Policies defined for stateful PCEs and PCCs should eventually fit in
the Policy-Enabled Path Computation Framework defined in [RFC5394],
and the framework should be extended to support Stateful PCEs.
9.2. Information and Data Models
PCEP session configuration and information in the PCEP MIB module
SHOULD be extended to include negotiated stateful capabilities,
synchronization status, and delegation status (at the PCC list PCEs
with delegated LSPs).
9.3. Liveness Detection and Monitoring
PCEP protocol extensions defined in this document do not require any
new mechanisms beyond those already defined in [RFC5440], Section
8.3.
9.4. Verifying Correct Operation
Mechanisms defined in [RFC5440], Section 8.4 also apply to PCEP
protocol extensions defined in this document. In addition to
monitoring parameters defined in [RFC5440], a stateful PCC-side PCEP
implementation SHOULD provide the following parameters:
o Total number of LSP updates
o Number of successful LSP updates
o Number of dropped LSP updates
o Number of LSP updates where LSP setup failed
A PCC implementation SHOULD provide a command to show for each LSP
whether it is delegated, and if so, to which PCE.
A PCC implementation SHOULD allow the operator to manually revoke LSP
delegation.
9.5. Requirements on Other Protocols and Functional Components
PCEP protocol extensions defined in this document do not put new
requirements on other protocols.
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9.6. Impact on Network Operation
Mechanisms defined in [RFC5440], Section 8.6 also apply to PCEP
protocol extensions defined in this document.
Additionally, a PCEP implementation SHOULD allow a limit to be placed
on the rate PCUpd and PCRpt messages sent by a PCEP speaker and
processed from a peer. It SHOULD also allow sending a notification
when a rate threshold is reached.
A PCC implementation SHOULD allow a limit to be placed on the rate of
LSP Updates to the same LSP to avoid signaling overload discussed in
Section 10.3.
10. Security Considerations
10.1. Vulnerability
This document defines extensions to PCEP to enable stateful PCEs.
The nature of these extensions and the delegation of path control to
PCEs results in more information being available for a hypothetical
adversary and a number of additional attack surfaces which must be
protected.
The security provisions described in [RFC5440] remain applicable to
these extensions. However, because the protocol modifications
outlined in this document allow the PCE to control path computation
timing and sequence, the PCE defense mechanisms described in
[RFC5440] section 7.2 are also now applicable to PCC security.
As a general precaution, it is RECOMMENDED that these PCEP extensions
only be activated on authenticated and encrypted sessions across PCEs
and PCCs belonging to the same administrative authority.
The following sections identify specific security concerns that may
result from the PCEP extensions outlined in this document along with
recommended mechanisms to protect PCEP infrastructure against related
attacks.
10.2. LSP State Snooping
The stateful nature of this extension explicitly requires LSP status
updates to be sent from PCC to PCE. While this gives the PCE the
ability to provide more optimal computations to the PCC, it also
provides an adversary with the opportunity to eavesdrop on decisions
made by network systems external to PCE. This is especially true if
the PCC delegates LSPs to multiple PCEs simultaneously.
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Adversaries may gain access to this information by eavesdropping on
unsecured PCEP sessions, and might then use this information in
various ways to target or optimize attacks on network infrastructure.
For example by flexibly countering anti-DDoS measures being taken to
protect the network, or by determining choke points in the network
where the greatest harm might be caused.
PCC implementations which allow concurrent connections to multiple
PCEs SHOULD allow the operator to group the PCEs by administrative
domains and they MUST NOT advertise LSP existence and state to a PCE
if the LSP is delegated to a PCE in a different group.
10.3. Malicious PCE
The LSP delegation mechanism described in this document allows a PCC
to grant effective control of an LSP to the PCE for the duration of a
PCEP session. While this enables PCE control of the timing and
sequence of path computations within and across PCEP sessions, it
also introduces a new attack vector: an attacker may flood the PCC
with PCUpd messages at a rate which exceeds either the PCC's ability
to process them or the network's ability to signal the changes,
either by spoofing messages or by compromising the PCE itself.
A PCC is free to revoke an LSP delegation at any time without needing
any justification. A defending PCC can do this by enqueueing the
appropriate PCRpt message. As soon as that message is enqueued in
the session, the PCC is free to drop any incoming PCUpd messages
without additional processing.
10.4. Malicious PCC
A stateful session also result in increased attack surface by placing
a requirement for the PCE to keep an LSP state replica for each PCC.
It is RECOMMENDED that PCE implementations provide a limit on
resources a single PCC can occupy.
Delegation of LSPs can create further strain on PCE resources and a
PCE implementation MAY preemptively give back delegations if it finds
itself lacking the resources needed to effectively manage the
delegation. Since the delegation state is ultimately controlled by
the PCC, PCE implementations SHOULD provide throttling mechanisms to
prevent strain created by flaps of either a PCEP session or an LSP
delegation.
11. Acknowledgements
We would like to thank Adrian Farrel, Cyril Margaria and Ramon
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Casellas for their contributions to this document.
We would like to thank Shane Amante, Julien Meuric, Kohei Shiomoto,
Paul Schultz and Raveendra Torvi for their comments and suggestions.
Thanks also to Cyril Margaria, Jon Hardwick, Dhruv Dhoddy, Oscar
Gonzales de Dios, Tomas Janciga, Stefan Kobza, Kexin Tang, Matej
Spanik, Jon Parker, Marek Zavodsky, Ambrose Kwong, Ashwin Sampath,
Calvin Ying and Xian Zhang for helpful comments and discussions.
12. References
12.1. Normative References
[I-D.ietf-pce-gmpls-pcep-extensions]
Margaria, C., Dios, O., and F. Zhang, "PCEP extensions for
GMPLS", draft-ietf-pce-gmpls-pcep-extensions-07 (work in
progress), October 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008.
[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"IS-IS Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5089, January 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
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May 2008.
[RFC5284] Swallow, G. and A. Farrel, "User-Defined Errors for RSVP",
RFC 5284, August 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
12.2. Informative References
[I-D.sivabalan-pce-disco-stateful]
Sivabalan, S., Medved, J., and X. Zhang, "IGP Extensions
for Stateful PCE Discovery",
draft-sivabalan-pce-disco-stateful-01 (work in progress),
April 2013.
[I-D.zhang-pce-stateful-pce-app]
Zhang, X. and I. Minei, "Applicability of Stateful Path
Computation Element (PCE)",
draft-zhang-pce-stateful-pce-app-04 (work in progress),
May 2013.
[MPLS-PC] Chaieb, I., Le Roux, JL., and B. Cousin, "Improved MPLS-TE
LSP Path Computation using Preemption", Global
Information Infrastructure Symposium, July 2007.
[MXMN-TE] Danna, E., Mandal, S., and A. Singh, "Practical linear
programming algorithm for balancing the max-min fairness
and throughput objectives in traffic engineering", pre-
print, 2011.
[NET-REC] Vasseur, JP., Pickavet, M., and P. Demeester, "Network
Recovery: Protection and Restoration of Optical, SONET-
SDH, IP, and MPLS", The Morgan Kaufmann Series in
Networking, June 2004.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
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[RFC3346] Boyle, J., Gill, V., Hannan, A., Cooper, D., Awduche, D.,
Christian, B., and W. Lai, "Applicability Statement for
Traffic Engineering with MPLS", RFC 3346, August 2002.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", RFC 5394,
December 2008.
[RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
Concurrent Optimization", RFC 5557, July 2009.
Authors' Addresses
Edward Crabbe
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: edc@google.com
Jan Medved
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
Email: jmedved@cisco.com
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Ina Minei
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: ina@juniper.net
Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava 821 05
Slovakia
Email: robert.varga@pantheon.sk
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