Inter Stateful Path Computation Element (PCE) Communication Procedures.
draft-litkowski-pce-state-sync-10
PCE Working Group S. Litkowski
Internet-Draft Cisco
Intended status: Standards Track S. Sivabalan
Expires: August 26, 2021 Ciena Corporation
C. Li
H. Zheng
Huawei Technologies
February 22, 2021
Inter Stateful Path Computation Element (PCE) Communication Procedures.
draft-litkowski-pce-state-sync-10
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computation in response to a Path Computation Client (PCC) request.
The Stateful PCE extensions allow stateful control of Multi-Protocol
Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths
(LSPs) using PCEP.
A Path Computation Client (PCC) can synchronize an LSP state
information to a Stateful Path Computation Element (PCE). The
stateful PCE extension allows a redundancy scenario where a PCC can
have redundant PCEP sessions towards multiple PCEs. In such a case,
a PCC gives control of a LSP to only a single PCE, and only one PCE
is responsible for path computation for this delegated LSP.
There are some use cases, where an inter-PCE stateful communication
can bring additional resiliency in the design, for instance when some
PCC-PCE session fails. The inter-PCE stateful communication may also
provide a faster update of the LSP states when such an event occurs.
Finally, when, in a redundant PCE scenario, there is a need to
compute a set of paths that are part of a group (so there is a
dependency between the paths), there may be some cases where the
computation of all paths in the group is not handled by the same PCE:
this situation is called a split-brain. This split-brain scenario
may lead to computation loops between PCEs or suboptimal path
computation.
This document describes the procedures to allow a stateful
communication between PCEs for various use-cases and also the
procedures to prevent computations loops.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
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This Internet-Draft will expire on August 26, 2021.
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Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . 3
1.1. Reporting LSP Changes . . . . . . . . . . . . . . . . . . 4
1.2. Split-Brain . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Applicability to H-PCE . . . . . . . . . . . . . . . . . 12
2. Proposed solution . . . . . . . . . . . . . . . . . . . . . . 12
2.1. State-sync session . . . . . . . . . . . . . . . . . . . 12
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2.2. Primary/Secondary relationship between PCE . . . . . . . 14
3. Procedures and Protocol Extensions . . . . . . . . . . . . . 14
3.1. Opening a state-sync session . . . . . . . . . . . . . . 14
3.1.1. Capability Advertisement . . . . . . . . . . . . . . 14
3.2. State synchronization . . . . . . . . . . . . . . . . . . 15
3.3. Incremental updates and report forwarding rules . . . . . 16
3.4. Maintaining LSP states from different sources . . . . . . 17
3.5. Computation priority between PCEs and sub-delegation . . 18
3.6. Passive stateful procedures . . . . . . . . . . . . . . . 19
3.7. PCE initiation procedures . . . . . . . . . . . . . . . . 20
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 24
5. Using Primary/Secondary Computation and State-sync Sessions
to increase Scaling . . . . . . . . . . . . . . . . . . . . . 25
6. PCEP-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
9.1. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 28
9.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 29
9.3. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction and Problem Statement
The Path Computation Element communication Protocol (PCEP) [RFC5440]
provides mechanisms for Path Computation Elements (PCEs) to perform
path computations in response to Path Computation Clients' (PCCs)
requests.
A stateful PCE [RFC8231] is capable of considering, for the purposes
of path computation, not only the network state in terms of links and
nodes (referred to as the Traffic Engineering Database or TED) but
also the status of active services (previously computed paths, and
currently reserved resources, stored in the Label Switched Paths
Database (LSP-DB).
[RFC8051] describes general considerations for a stateful PCE
deployment and examines its applicability and benefits, as well as
its challenges and limitations through a number of use cases.
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The examples in this section are for illustrative purpose to showcase
the need for inter-PCE stateful PCEP sessions.
1.1. Reporting LSP Changes
When using a stateful PCE ([RFC8231]), a PCC can synchronize an LSP
state information to the stateful PCE. If the PCC grants the control
of the LSP to the PCE (called delegation [RFC8231]), the PCE can
update the LSP parameters at any time.
In a multi PCE deployment (redundancy, loadbalancing...), with the
current specification defined in [RFC8231], when a PCE makes an
update, it is the PCC that is in charge of reporting the LSP status
to all PCEs with LSP parameter change which brings additional hops
and delays in notifying the overall network of the LSP parameter
change.
This delay may affect the reaction time of the other PCEs if they
need to take action after being notified of the LSP parameter change.
Apart from the synchronization from the PCC, it is also useful if
there is a synchronization mechanism between the stateful PCEs. As
stateful PCE make changes to its delegated LSPs, these changes
(pending LSPs and the sticky resources [RFC7399]) can be synchronized
immediately to the other PCEs.
+----------+
| PCC1 | LSP1
+----------+
/ \
/ \
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
\ /
\ /
+----------+
| PCC2 | LSP2
+----------+
In the figure above, we consider a load-balanced PCE architecture, so
PCE1 is responsible to compute paths for PCC1 and PCE2 is responsible
to compute paths for PCC2. When PCE1 triggers an LSP update for
LSP1, it sends a PCUpd message to PCC1 containing the new parameters
for LSP1. PCC1 will take the parameters into account and will send a
PCRpt message to PCE1 and PCE2 reflecting the changes. PCE2 will so
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be notified of the change only after receiving the PCRpt message from
PCC1.
Let's consider that the LSP1 parameters changed in such a way that
LSP1 will take over resources from LSP2 with a higher priority.
After receiving the report from PCC1, PCE2 will therefore try to find
a new path for LSP2. If we consider that there is a round trip delay
of about 150 milliseconds (ms) between the PCEs and PCC1 and a round
trip delay of 10 ms between the two PCEs if will take more than 150
ms for PCE2 to be notified of the change.
Adding a PCEP session between PCE1 and PCE2 may allow to reduce the
synchronization time, so PCE2 can react more quickly by taking the
pending LSPs and attached resources into account during path
computation and re-optimization.
1.2. Split-Brain
In a resiliency case, a PCC has redundant PCEP sessions towards
multiple PCEs. In such a case, a PCC gives control on an LSP to a
single PCE only, and only this PCE is responsible for the path
computation for the delegated LSP: the PCC achieves this by setting
the D flag only towards the active PCE [RFC8231] selected for
delegation. The election of the active PCE to delegate an LSP is
controlled by each PCC. The PCC usually elects the active PCE by a
local configured policy (by setting a priority). Upon PCEP session
failure, or active PCE failure, PCC may decide to elect a new active
PCE by sending new PCRpt message with D flag set to this new active
PCE. When the failed PCE or PCEP session comes back online, it will
be up to the implementation to do preemption. Doing preemption may
lead to some disruption on the existing path if path results from
both PCEs are not exactly the same. By considering a network with
multiple PCCs and implementing multiple stateful PCEs for redundancy
purpose, there is no guarantee that at any time all the PCCs delegate
their LSPs to the same PCE.
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+----------+
| PCC1 | LSP1
+----------+
/ \
/ \
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
\ /
*fail* \ /
+----------+
| PCC2 | LSP2
+----------+
In the example above, we consider that by configuration, both PCCs
will firstly delegate their LSPs to PCE1. So, PCE1 is responsible
for computing a path for both LSP1 and LSP2. If the PCEP session
between PCC2 and PCE1 fails, PCC2 will delegate LSP2 to PCE2. So
PCE1 becomes responsible only for LSP1 path computation while PCE2 is
responsible for the path computation of LSP2. When the PCC2-PCE1
session is back online, PCC2 will keep using PCE2 as active PCE
(consider no preemption in this example). So the result is a
permanent situation where each PCE is responsible for a subset of
path computation.
This situation is called a split-brain scenario, as there are
multiple computation brains running at the same time while a central
computation unit was required in some deployments/use cases.
Further, there are use cases where a particular LSP path computation
is linked to another LSP path computation: the most common use case
is path disjointness (see [RFC8800]). The set of LSPs that are
dependent to each other may start from a different head-end.
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_________________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ +------+ |
| | PCC1 | ----------------------> | PCC2 | |
| +------+ +------+ |
| |
| |
| +------+ +------+ |
| | PCC3 | ----------------------> | PCC4 | |
| +------+ +------+ |
| |
\ /
\_________________________________________/
_________________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ 10 +------+ |
| | PCC1 | ----- R1 ---- R2 ------- | PCC2 | |
| +------+ | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | PCC3 | ----- R3 ---- R4 ------- | PCC4 | |
| +------+ +------+ |
| |
\ /
\_________________________________________/
In the figure above, the requirement is to create two link-disjoint
LSPs: PCC1->PCC2 and PCC3->PCC4. In the topology, all links cost
metric is set to 1 except for the link 'R1-R2' which has a metric of
10. The PCEs are responsible for the path computation and PCE1 is
the active primary PCE for all PCCs in the nominal case.
Scenario 1:
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In the normal case (PCE1 as active primary PCE), consider that
PCC1->PCC2 LSP is configured first with the link disjointness
constraint, PCE1 sends a PCUpd message to PCC1 with the ERO:
R1->R3->R4->R2->PCC2 (shortest path). PCC1 signals and installs the
path. When PCC3->PCC4 is configured, the PCEs already knows the path
of PCC1->PCC2 and can compute a link-disjoint path: the solution
requires to move PCC1->PCC2 onto a new path to let room for the new
LSP. PCE1 sends a PCUpd message to PCC1 with the new ERO:
R1->R2->PCC2 and a PCUpd to PCC3 with the following ERO:
R3->R4->PCC4. In the normal case, there is no issue for PCE1 to
compute a link-disjoint path.
Scenario 2:
Consider that PCC1 lost its PCEP session with PCE1 (all other PCEP
sessions are UP). PCC1 delegates its LSP to PCE2.
+----------+
| PCC1 | LSP: PCC1->PCC2
+----------+
\
\ D=1
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
D=1 \ / D=0
\ /
+----------+
| PCC3 | LSP: PCC3->PCC4
+----------+
Consider that the PCC1->PCC2 LSP is configured first with the link
disjointness constraint, PCE2 (which is the new active primary PCE
for PCC1) sends a PCUpd message to PCC1 with the ERO:
R1->R3->R4->R2->PCC2 (shortest path). When PCC3->PCC4 is configured,
PCE1 is not aware of LSPs from PCC1 any more, so it cannot compute a
disjoint path for PCC3->PCC4 and will send a PCUpd message to PCC3
with the shortest path ERO: R3->R4->PCC4. When PCC3->PCC4 LSP will
be reported to PCE2 by PCC3, PCE2 will ensure disjointness
computation and will correctly move PCC1->PCC2 (as it owns delegation
for this LSP) on the following path: R1->R2->PCC2. With this
sequence of event and these PCEP sessions, disjointness is ensured.
Scenario 3:
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+----------+
| PCC1 | LSP: PCC1->PCC2
+----------+
/ \
D=1 / \ D=0
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
/ D=1
/
+----------+
| PCC3 | LSP: PCC3->PCC4
+----------+
Consider the above PCEP sessions and the PCC1->PCC2 LSP is configured
first with the link disjointness constraint, PCE1 computes the
shortest path as it is the only LSP in the disjoint association group
that it is aware of: R1->R3->R4->R2->PCC2 (shortest path). When
PCC3->PCC4 is configured, PCE2 must compute a disjoint path for this
LSP. The only solution found is to move PCC1->PCC2 LSP on another
path, but PCE2 cannot do it as it does not have delegation for this
LSP. In this set-up, PCEs are not able to find a disjoint path.
Scenario 4:
+----------+
| PCC1 | LSP: PCC1->PCC2
+----------+
/ \
D=1 / \ D=0
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
D=0 \ / D=1
\ /
+----------+
| PCC3 | LSP: PCC3->PCC4
+----------+
Consider the above PCEP sessions and that PCEs are configured to
fall-back to the shortest path if disjointness cannot be found as
described in [RFC8800]. The PCC1->PCC2 LSP is configured first, PCE1
computes the shortest path as it is the only LSP in the disjoint
association group that it is aware of: R1->R3->R4->R2->PCC2 (shortest
path). When PCC3->PCC4 is configured, PCE2 must compute a disjoint
path for this LSP. The only solution found is to move PCC1->PCC2 LSP
on another path, but PCE2 cannot do it as it does not have delegation
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for this LSP. PCE2 then provides the shortest path for PCC3->PCC4:
R3->R4->PCC4. When PCC3 receives the ERO, it reports it back to both
PCEs. When PCE1 becomes aware of the PCC3->PCC4 path, it recomputes
the constrained shortest path first (CSPF) algorithm and provides a
new path for PCC1->PCC2: R1->R2->PCC2. The new path is reported back
to all PCEs by PCC1. PCE2 recomputes also CSPF to take into account
the new reported path. The new computation does not lead to any path
update.
Scenario 5:
_____________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ 100 +------+ |
| | | -------------------- | | |
| | PCC1 | ----- R1 ----------- | PCC2 | |
| +------+ | +------+ |
| | | | |
| 6 | | 2 | 2 |
| | | | |
| +------+ | +------+ |
| | PCC3 | ----- R3 ----------- | PCC4 | |
| +------+ 10 +------+ |
| |
\ /
\_____________________________________/
Now, consider a new network topology with the same PCEP sessions as
the previous example. Suppose that both LSPs are configured almost
at the same time. PCE1 will compute a path for PCC1->PCC2 while PCE2
will compute a path for PCC3->PCC4. As each PCE is not aware of the
path of the second LSP in the association group (not reported yet),
each PCE is computing the shortest path for the LSP. PCE1 computes
ERO: R1->PCC2 for PCC1->PCC2 and PCE2 computes ERO:
R3->R1->PCC2->PCC4 for PCC3->PCC4. When these shortest paths will be
reported to each PCE. Each PCE will recompute disjointness. PCE1
will provide a new path for PCC1->PCC2 with ERO: PCC1->PCC2. PCE2
will provide also a new path for PCC3->PCC4 with ERO: R3->PCC4. When
those new paths will be reported to both PCEs, this will trigger CSPF
again. PCE1 will provide a new more optimal path for PCC1->PCC2 with
ERO: R1->PCC2 and PCE2 will also provide a more optimal path for
PCC3->PCC4 with ERO: R3->R1->PCC2->PCC4. So we come back to the
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initial state. When those paths will be reported to both PCEs, this
will trigger CSPF again. An infinite loop of CSPF computation is
then happening with a permanent flap of paths because of the split-
brain situation.
This permanent computation loop comes from the inconsistency between
the state of the LSPs as seen by each PCE due to the split-brain:
each PCE is trying to modify at the same time its delegated path
based on the last received path information which de facto
invalidates this received path information.
Scenario 6: multi-domain
Domain/Area 1 Domain/Area 2
________________ ________________
/ \ / \
/ +------+ | | +------+ \
| | PCE1 | | | | PCE3 | |
| +------+ | | +------+ |
| | | |
| +------+ | | +------+ |
| | PCE2 | | | | PCE4 | |
| +------+ | | +------+ |
| | | |
| +------+ | | +------+ |
| | PCC1 | | | | PCC2 | |
| +------+ | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | PCC3 | | | | PCC4 | |
| +------+ | | +------+ |
\ | | |
\_______________/ \________________/
In the example above, suppose that the disjoint LSPs from PCC1 to
PCC2 and from PCC4 to PCC3 are created. All the PCEs have the
knowledge of both domain topologies (e.g. using BGP-LS [RFC7752]).
For operation/management reasons, each domain uses its own group of
redundant PCEs. PCE1/PCE2 in domain 1 have PCEP sessions with PCC1
and PCC3 while PCE3/PCE4 in domain 2 have PCEP sessions with PCC2 and
PCC4. As PCE1/2 does not know about LSPs from PCC2/4 and PCE3/4 do
not know about LSPs from PCC1/3, there is no possibility to compute
the disjointness constraint. This scenario can also be seen as a
split-brain scenario. This multi-domain architecture (with multiple
groups of PCEs) can also be used in a single domain, where an
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operator wants to limit the failure domain by creating multiple
groups of PCEs maintaining a subset of PCCs. As for the multi-domain
example, there will be no possibility to compute the disjoint path
starting from head-ends managed by different PCE groups.
In this document, we propose a solution that addresses the
possibility to compute LSP association based constraints (like
disjointness) in split-brain scenarios while preventing computation
loops.
1.3. Applicability to H-PCE
[RFC8751] describes general considerations and use cases for the
deployment of Stateful PCE(s) using the Hierarchical PCE [RFC6805]
architecture. In this architecture, there is a clear need to
communicate between a child stateful PCE and a parent stateful PCE.
The procedures and extensions as described in Section 3 are equally
applicable to the H-PCE scenario.
2. Proposed solution
Our solution is based on :
o The creation of the inter-PCE stateful PCEP session with specific
procedures.
o A Primary/Secondary relationship between PCEs.
2.1. State-sync session
This document proposes to set-up a PCEP session between the stateful
PCEs. Creating such a session is already authorized by multiple
scenarios like the one described in [RFC4655] (multiple PCEs that are
handling part of the path computation) and [RFC6805] (hierarchical
PCE) but was only focused on the stateless PCEP sessions. As
stateful PCE brings additional features (LSP state synchronization,
path update, delegation, ...), thus some new behaviors need to be
defined.
This inter-PCE PCEP session will allow the exchange of LSP states
between PCEs that would help some scenarios where PCEP sessions are
lost between PCC and PCE. This inter-PCE PCEP session is henceforth
called a state-sync session.
For example, in the scenario below, there is no possibility to
compute disjointness as there is no PCE that is aware of both LSPs.
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+----------+
| PCC1 | LSP: PCC1->PCC2
+----------+
/
D=1 /
+---------+ +---------+
| PCE1 | | PCE2 |
+---------+ +---------+
/ D=1
/
+----------+
| PCC3 | LSP: PCC3->PCC4
+----------+
If we add a state-sync session, PCE1 will be able to do state
synchronization via PCRpt messages for its LSP to PCE2 and PCE2 will
do the same. All the PCEs will be aware of all LSPs even if a
PCC->PCE session is down. PCEs will then be able to compute disjoint
paths.
+----------+
| PCC1 | LSP : PCC1->PCC2
+----------+
/
D=1 /
+---------+ PCEP +---------+
| PCE1 | ----- | PCE2 |
+---------+ +---------+
/ D=1
/
+----------+
| PCC3 | LSP : PCC3->PCC4
+----------+
The procedures associated with this state-sync session are defined in
Section 3.
By just adding this state-sync session, it does not ensure that a
path with LSP association based constraints can always be computed
and does not prevent the computation loop, but it increases
resiliency and ensures that PCEs will have the state information for
all LSPs. Also, this session will allow for a PCE to update the
other PCEs providing a faster synchronization mechanism than relying
on PCCs only.
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2.2. Primary/Secondary relationship between PCE
As seen in Section 1, performing a path computation in a split-brain
scenario (multiple PCEs responsible for computation) may provide a
non-optimal LSP placement, no path, or computation loops. To provide
the best efficiency, an LSP association constraint-based computation
requires that a single PCE performs the path computation for all LSPs
in the association group. Note that, it could be all LSPs belonging
to a particular association group, or all LSPs from a particular PCC,
or all LSPs in the network that need to be delegated to a single PCE
based on the deployment scenarios.
This document proposes to add a priority mechanism between PCEs to
elect a single computing PCE. Using this priority mechanism, PCEs
can agree on the PCE that will be responsible for the computation for
a particular association group, or set of LSPs. The priority could
be set per association, per PCC, or for all LSPs. How this priority
is set or advertised is out of the scope of this document. The rest
of the text considers the association group as an example.
When a single PCE is performing the computation for a particular
association group, no computation loop can happen and an optimal
placement will be provided. The other PCEs will only act as state
collectors and forwarders.
In the scenario described in Section 2.1, PCE1 and PCE2 will decide
that PCE1 will be responsible for the path computation of both LSPs.
If we first configure PCC1->PCC2, PCE1 computes the shortest path at
it is the only LSP in the disjoint-group that it is aware of:
R1->R3->R4->R2->PCC2 (shortest path). When PCC3->PCC4 is configured,
PCE2 will not perform computation even if it has delegation but
forwards the delegation via PCRpt message to PCE1 through the state-
sync session. PCE1 will then perform disjointness computation and
will move PCC1->PCC2 onto R1->R2->PCC2 and provides an ERO to PCE2
for PCC3->PCC4: R3->R4->PCC4. The PCE2 will further update the PCC3
with the new path.
3. Procedures and Protocol Extensions
3.1. Opening a state-sync session
3.1.1. Capability Advertisement
A PCE indicates its support of state-sync procedures during the PCEP
Initialization phase [RFC5440]. The OPEN object in the Open message
MUST contains the "Stateful PCE Capability" TLV defined in [RFC8231].
A new P (INTER-PCE-CAPABILITY) flag is introduced to indicate the
support of state-sync.
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This document adds a new bit in the Flags field with :
P (INTER-PCE-CAPABILITY - 1 bit - TBD4): If set to 1 by a PCEP
Speaker, the PCEP speaker indicates that the session MUST follow
the state-sync procedures as described in this document. The P
bit MUST be set by both speakers: if a PCEP Speaker receives a
STATEFUL-PCE-CAPABILITY TLV with P=0 while it advertised P=1 or if
both set P flag to 0, the session SHOULD be set-up but the state-
sync procedures MUST NOT be applied on this session.
The U flag [RFC8231] MUST be set when sending the STATEFUL-PCE-
CAPABILITY TLV with the P flag set. In case the U flag is not set
along with the P flag, the state sync capability is not enabled and
it is considered as if the P flag is not set. The S flag MAY be set
if optimized synchronization is required as per [RFC8232].
3.2. State synchronization
When the state sync capability has been negotiated between stateful
PCEs, each PCEP speaker will behave as a PCE and as a PCC at the same
time regarding the state synchronization as defined in [RFC8231].
This means that each PCEP Speaker:
o MUST send a PCRpt message towards its neighbor with S flag set for
each LSP in its LSP database learned from a PCC. (PCC role)
o MUST send the End Of Synchronization Marker towards its neighbor
when all LSPs have been reported. (PCC role)
o MUST wait for the LSP synchronization from its neighbor to end
(receiving an End Of Synchronization Marker). (PCE role)
The process of synchronization runs in parallel on each PCE (with no
defined order).
The optimized state synchronization procedures MAY be used, as
defined in [RFC8232].
When a PCEP Speaker sends a PCRpt on a state-sync session, it MUST
add the SPEAKER-IDENTITY-TLV (defined in [RFC8232]) in the LSP
Object, the value used will refer to the 'owner' PCC of the LSP. If
a PCEP Speaker receives a PCRpt on a state-sync session without this
TLV, it MUST discard the PCRpt message and it MUST reply with a PCErr
message using error-type=6 (Mandatory Object missing) and error-
value=TBD1 (SPEAKER-IDENTITY-TLV missing).
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3.3. Incremental updates and report forwarding rules
During the life of an LSP, its state may change (path, constraints,
operational state...) and a PCC will advertise a new PCRpt to the PCE
for each such change.
When propagating LSP state changes from a PCE to other PCEs, it is
mandatory to ensure that a PCE always uses the freshest state coming
from the PCC.
When a PCE receives a new PCRpt from a PCC with the LSP-DB-VERSION,
the PCE MUST forward the PCRpt to all its state-sync sessions and
MUST add the appropriate SPEAKER-IDENTITY-TLV in the PCRpt. In
addition, it MUST add a new ORIGINAL-LSP-DB-VERSION TLV (described
below). The ORIGINAL-LSP-DB-VERSION contains the LSP-DB-VERSION
coming from the PCC.
When a PCE receives a new PCRpt from a PCC without the LSP-DB-
VERSION, it SHOULD NOT forward the PCRpt on any state-sync sessions
and log such an event on the first occurrence.
When a PCE receives a new PCRpt from a PCC with the R flag (Remove)
set and an LSP-DB-VERSION TLV, the PCE MUST forward the PCRpt to all
its state-sync sessions keeping the R flag set (Remove) and MUST add
the appropriate SPEAKER-IDENTITY-TLV and ORIGINAL-LSP-DB-VERSION TLV
in the PCRpt message.
When a PCE receives a PCRpt from a state-sync session, it MUST NOT
forward the PCRpt to other state-sync sessions. This helps to
prevent message loops between PCEs. As a consequence, a full mesh of
PCEP sessions between PCEs are REQUIRED.
When a PCRpt is forwarded, all the original objects and values are
kept. As an example, the PLSP-ID used in the forwarded PCRpt will be
the same as the original one used by the PCC. Thus an implementation
supporting this document MUST consider SPEAKER-IDENTITY-TLV and PLSP-
ID together to uniquely identify an LSP on the state-sync session.
The ORIGINAL-LSP-DB-VERSION TLV is encoded as follows and MUST always
contain the LSP-DB-VERSION received from the owner PCC of the LSP:
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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=TBD2 | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP State DB Version Number |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Using the ORIGINAL-LSP-DB-VERSION TLV allows a PCE to keep using
optimized synchronization ([RFC8232]) with another PCE. In such a
case, the PCE will send a PCRpt to another PCE with both ORIGINAL-
LSP-DB-VERSION TLV and LSP-DB-VERSION TLV. The ORIGINAL-LSP-DB-
VERSION TLV will contain the version number as allocated by the PCC
while the LSP-DB-VERSION will contain the version number allocated by
the local PCE.
3.4. Maintaining LSP states from different sources
When a PCE receives a PCRpt on a state-sync session, it stores the
LSP information into the original PCC address context (as the LSP
belongs to the PCC). A PCE SHOULD maintain a single state for a
particular LSP and SHOULD maintain the list of sources it learned a
particular state from.
A PCEP speaker may receive state information for a particular LSP
from different sources: the PCC that owns the LSP (through a regular
PCEP session) and some PCEs (through PCEP state-sync sessions). A
PCEP speaker MUST always keep the freshest state in its LSP database,
overriding the previously received information.
A PCE, receiving a PCRpt from a PCC, updates the state of the LSP in
its LSP-DB with the newly received information. When receiving a
PCRpt from another PCE, a PCE SHOULD update the LSP state only if the
ORIGINAL-LSP-DB-VERSION present in the PCRpt is greater than the
current ORIGINAL-LSP-DB-VERSION of the stored LSP state. This
ensures that a PCE never tries to update its stored LSP state with an
old information. Each time a PCE updates an LSP state in its LSP-DB,
it SHOULD reset the source list associated with the LSP state and
SHOULD add the source speaker address in the source list. When a PCE
receives a PCRpt which has an ORIGINAL-LSP-DB-VERSION (if coming from
a PCE) or an LSP-DB-VERSION (if coming from the PCC) equals to the
current ORIGINAL-LSP-DB-VERSION of the stored LSP state, it SHOULD
add the source speaker address in the source list.
When a PCE receives a PCRpt requesting an LSP deletion from a
particular source, it SHOULD remove this particular source from the
list of sources associated with this LSP.
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When the list of sources becomes empty for a particular LSP, the LSP
state MUST be removed. This means that all the sources must send a
PCRpt with R=1 for an LSP to make the PCE remove the LSP state.
3.5. Computation priority between PCEs and sub-delegation
A computation priority is necessary to ensure that a single PCE will
perform the computation for all the LSPs in an association group:
this will allow for a more optimized LSP placement and will prevent
computation loops.
All PCEs in the network that are handling LSPs in a common LSP
association group SHOULD be aware of each other including the
computation priority of each PCE. Note that there is no need for PCC
to be aware of this. The computation priority is a number and the
PCE having the highest priority SHOULD be responsible for the
computation. If several PCEs have the same priority value, their IP
address SHOULD be used as a tie-breaker to provide a rank: the
highest IP address has more priority. How PCEs are aware of the
priority of each other is out of the scope of this document, but as
example learning priorities could be done through PCE discovery or
local configuration.
The definition of the priority could be global so the highest
priority PCE will handle all path computations or more granular, so a
PCE may have the highest priority for only a subset of LSPs or
association-groups.
A PCEP Speaker receiving a PCRpt from a PCC with the D flag set that
does not have the highest computation priority, SHOULD forward the
PCRpt on all state-sync sessions (as per Section 3.3) and SHOULD set
D flag on the state-sync session towards the highest priority PCE, D
flag will be unset to all other state-sync sessions. This behavior
is similar to the delegation behavior handled at the PCC side and is
called a sub-delegation (the PCE sub-delegates the control of the LSP
to another PCE). When a PCEP Speaker sub-delegates an LSP to another
PCE, it loose control of the LSP and cannot update it anymore by its
own decision. When a PCE receives a PCRpt with D flag set on a
state-sync session, as a regular PCE, it is granted control over the
LSP.
If the highest priority PCE is failing or if the state-sync session
between the local PCE and the highest priority PCE failed, the local
PCE MAY decide to delegate the LSP to the next highest priority PCE
or to take back control of the LSP. It is a local policy decision.
When a PCE has the delegation for an LSP and needs to update this
LSP, it MUST send a PCUpd message to all state-sync sessions and to
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the PCC session on which it received the delegation. The D-Flag
would be unset in the PCUpd for state-sync sessions whereas the
D-Flag would be set for the PCC. In the case of sub-delegation, the
computing PCE will send the PCUpd only to all state-sync sessions (as
it has no direct delegation from a PCC). The D-Flag would be set for
the state-sync session to the PCE that sub-delegated this LSP and the
D-Flag would be unset for other state-sync sessions.
The PCUpd sent over a state-sync session MUST contain the SPEAKER-
IDENTITY-TLV in the LSP Object (the value used must identify the
target PCC). The PLSP-ID used is the original PLSP-ID generated by
the PCC and learned from the forwarded PCRpt. If a PCE receives a
PCUpd on a state-sync session without the SPEAKER-IDENTITY-TLV, it
MUST discard the PCUpd and MUST reply with a PCErr message using
error-type=6 (Mandatory Object missing) and error-value=TBD1
(SPEAKER-IDENTITY-TLV missing).
When a PCE receives a valid PCUpd on a state-sync session, it SHOULD
forward the PCUpd to the appropriate PCC (identified based on the
SPEAKER-IDENTITY-TLV value) that delegated the LSP originally and
SHOULD remove the SPEAKER-IDENTITY-TLV from the LSP Object. The
acknowledgment of the PCUpd is done through a cascaded mechanism, and
the PCC is the only responsible for triggering the acknowledgment:
when the PCC receives the PCUpd from the local PCE, it acknowledges
it with a PCRpt as per [RFC8231]. When receiving the new PCRpt from
the PCC, the local PCE uses the defined forwarding rules on the
state-sync session so the acknowledgment is relayed to the computing
PCE.
A PCE SHOULD NOT compute a path using an association-group constraint
if it has delegation for only a subset of LSPs in the group. In this
case, an implementation MAY use a local policy on PCE to decide if
PCE does not compute path at all for this set of LSP or if it can
compute a path by relaxing the association-group constraint.
3.6. Passive stateful procedures
In the passive stateful PCE architecture, the PCC is responsible for
triggering a path computation request using a PCReq message to its
PCE. Similarly to PCRpt Message, which remains unchanged for passive
mode, if a PCE receives a PCReq for an LSP and if this PCE finds that
it does not have the highest computation priority of this LSP, or
groups..., it MUST forward the PCReq message to the highest priority
PCE over the state-sync session. When the highest priority PCE
receives the PCReq, it computes the path and generates a PCRep
message towards the PCE that made the request. This PCE will then
forward the PCRep to the requesting PCC. The handling of LSP object
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and the SPEAKER-IDENTITY-TLV in PCReq and PCRep is similar to PCRpt/
PCUpd messages.
3.7. PCE initiation procedures
It is possible that a PCE does not have a PCEP session with the
headend to initiate a LSP as per [RFC8281]. A PCE could send the
PCInitiate message on the state-sync sessions to other PCE to request
it to create a PCE-Initiated LSP on its behalf. If the PCE is able
to initiate the LSP it would report it on the state-sync session via
PCRpt message. If the PCE does not have a session to the headend, it
MUST send a PCErr message with Error-type=24 (PCE instantiation
error) and Error-value=TBD5 (No PCEP session with the headend). PCE
could try to initiate via another state-sync PCE if available.
4. Examples
The examples in this section are for illustrative purpose to show how
the behavior of the state sync inter-PCE sessions.
4.1. Example 1
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_________________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ 10 +------+ |
| | PCC1 | ----- R1 ---- R2 ------- | PCC2 | |
| +------+ | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | PCC3 | ----- R3 ---- R4 ------- | PCC4 | |
| +------+ +------+ |
| |
\ /
\_________________________________________/
+----------+
| PCC1 | LSP : PCC1->PCC2
+----------+
/
D=1 /
+---------+ +---------+
| PCE1 |----| PCE2 |
+---------+ +---------+
/ D=1
/
+----------+
| PCC3 | LSP : PCC3->PCC4
+----------+
PCE1 computation priority 100
PCE2 computation priority 200
Consider the PCEP sessions as shown above, where computation priority
is global for all the LSPs and link disjoint between LSPs PCC1->PCC2
and PCC3->PCC4 is required.
Consider the PCC1->PCC2 is configured first and PCC1 delegates the
LSP to PCE1, but as PCE1 does not have the highest computation
priority, it sub-delegates the LSP to PCE2 by sending a PCRpt with
D=1 and including the SPEAKER-IDENTITY-TLV over the state-sync
session. PCE2 receives the PCRpt and as it has delegation for this
LSP, it computes the shortest path: R1->R3->R4->R2->PCC2. It then
sends a PCUpd to PCE1 (including the SPEAKER-IDENTITY-TLV) with the
computed ERO. PCE1 forwards the PCUpd to PCC1 (removing the SPEAKER-
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IDENTITY-TLV). PCC1 acknowledges the PCUpd by a PCRpt to PCE1. PCE1
forwards the PCRpt to PCE2.
When PCC3->PCC4 is configured, PCC3 delegates the LSP to PCE2, PCE2
can compute a disjoint path as it has knowledge of both LSPs and has
delegation also for both. The only solution found is to move
PCC1->PCC2 LSP on another path, PCE2 can move PCC1->PCC2 as it has
sub-delegation for it. It creates a new PCUpd with a new ERO:
R1->R2-PCC2 towards PCE1 which forwards to PCC1. PCE2 sends a PCUpd
to PCC3 with the path: R3->R4->PCC4.
In this set-up, PCEs are able to find a disjoint path while without
state-sync and computation priority they could not.
4.2. Example 2
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_____________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ 100 +------+ |
| | | -------------------- | | |
| | PCC1 | ----- R1 ----------- | PCC2 | |
| +------+ | +------+ |
| | | | |
| 6 | | 2 | 2 |
| | | | |
| +------+ | +------+ |
| | PCC3 | ----- R3 ----------- | PCC4 | |
| +------+ 10 +------+ |
| |
\ /
\_____________________________________/
+----------+
| PCC1 | LSP : PCC1->PCC2
+----------+
/ \
D=1 / \ D=0
+---------+ +---------+
| PCE1 |----| PCE2 |
+---------+ +---------+
D=0 \ / D=1
\ /
+----------+
| PCC3 | LSP : PCC3->PCC4
+----------+
PCE1 computation priority 200
PCE2 computation priority 100
In this example, suppose both LSPs are configured almost at the same
time. PCE1 sub-delegates PCC1->PCC2 to PCE2 while PCE2 keeps
delegation for PCC3->PCC4, PCE2 computes a path for PCC1->PCC2 and
PCC3->PCC4 and can achieve disjointness computation easily. No
computation loop happens in this case.
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4.3. Example 3
_________________________________________
/ \
/ +------+ +------+ \
| | PCE1 | | PCE2 | |
| +------+ +------+ |
| |
| +------+ 10 +------+ |
| | PCC1 | ----- R1 ---- R2 ------- | PCC2 | |
| +------+ | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | PCC3 | ----- R3 ---- R4 ------- | PCC4 | |
| +------+ +------+ |
| |
\ /
\_________________________________________/
+----------+
| PCC1 | LSP : PCC1->PCC2
+----------+
/
D=1 /
+---------+ +---------+ +---------+
| PCE1 |----| PCE2 |----| PCE3 |
+---------+ +---------+ +---------+
/ D=1
/
+----------+
| PCC3 | LSP : PCC3->PCC4
+----------+
PCE1 computation priority 100
PCE2 computation priority 200
PCE3 computation priority 300
With the PCEP sessions as shown above, consider the need to have link
disjoint LSPs PCC1->PCC2 and PCC3->PCC4.
Suppose PCC1->PCC2 is configured first, PCC1 delegates the LSP to
PCE1, but as PCE1 does not have the highest computation priority, it
will sub-delegate the LSP to PCE2 (as it not aware of PCE3 and has no
way to reach it). PCE2 cannot compute a path for PCC1->PCC2 as it
does not have the highest priority and is not allowed to sub-delegate
the LSP again towards PCE3 as per Section 3.
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When PCC3->PCC4 is configured, PCC3 delegates the LSP to PCE2 that
performs sub-delegation to PCE3. As PCE3 will have knowledge of only
one LSP in the group, it cannot compute disjointness and can decide
to fall-back to a less constrained computation to provide a path for
PCC3->PCC4. In this case, it will send a PCUpd to PCE2 that will be
forwarded to PCC3.
Disjointness cannot be achieved in this scenario because of lack of
state-sync session between PCE1 and PCE3, but no computation loop
happens. Thus it is advised for all PCEs that support state-sync to
have a full mesh sessions between each other.
5. Using Primary/Secondary Computation and State-sync Sessions to
increase Scaling
The Primary/Secondary computation and state-sync sessions
architecture can be used to increase the scaling of the PCE
architecture. If the number of PCCs is really high, it may be too
resource consuming for a single PCE to maintain all the PCEP sessions
while at the same time performing all path computations. Using
primary/secondary computation and state-sync sessions may allow to
create groups of PCEs that manage a subset of the PCCs and perform
some or no path computations. Decoupling PCEP session maintenance
and computation will allow increasing scaling of the PCE
architecture.
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+----------+
| PCC500 |
+----------+-+
| PCC1 |
+----------+
/ \
/ \
+---------+ +---------+
| PCE1 |---| PCE2 |
+---------+ +---------+
| \ / |
| \/ |
| /\ |
| / \ |
+---------+ +---------+
| PCE3 |---| PCE4 |
+---------+ +---------+
\ /
\ /
+----------+
| PCC501 |
+----------+-+
| PCC1000 |
+----------+
In the figure above, two groups of PCEs are created: PCE1/2 maintain
PCEP sessions with PCC1 up to PCC500, while PCE3/4 maintain PCEP
sessions with PCC501 up to PCC1000. A granular primary/secondary
policy is set-up as follows to load-share computation between PCEs:
o PCE1 has priority 200 for association ID 1 up to 300, association
source 0.0.0.0. All other PCEs have a decreasing priority for
those associations.
o PCE3 has priority 200 for association ID 301 up to 500,
association source 0.0.0.0. All other PCEs have a decreasing
priority for those associations.
If some PCCs delegate LSPs with association ID 1 up to 300 and
association source 0.0.0.0, the receiving PCE (if not PCE1) will sub-
delegate the LSPs to PCE1. PCE1 becomes responsible for the
computation of these LSP associations while PCE3 is responsible for
the computation of another set of associations.
The procedures described in this document could help greatly in load-
sharing between a group of stateful PCEs.
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6. PCEP-PATH-VECTOR TLV
This document allows PCEP messages to be propagated among PCEP
speaker. It may be useful to track information about the propagation
of the messages. One of the use cases is a message loop detection
mechanism, but other use cases like hop by hop information recording
may also be implemented.
This document introduces the PCEP-PATH-VECTOR TLV (type TBD3) with
the following format:
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=TBD3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PCEP-SPEAKER-INFORMATION#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PCEP-SPEAKER-INFORMATION#n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The TLV format and padding rules are as per [RFC5440].
The PCEP-SPEAKER-INFORMATION field has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | ID Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Speaker Entity identity (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SubTLVs (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length: defines the total length of the PCEP-SPEAKER-INFORMATION
field.
ID Length: defines the length of the Speaker identity actual field
(non-padded).
Speaker Entity identity: same possible values as the SPEAKER-
IDENTIFIER-TLV. Padded with trailing zeros to a 4-byte boundary.
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The PCEP-SPEAKER-INFORMATION may also carry some optional subTLVs
so each PCEP speaker can add local information that could be
recorded. This document does not define any sub-TLV.
The PCEP-PATH-VECTOR TLV MAY be carried in the LSP Object. Its usage
is purely optional.
The list of speakers within the PCEP-PATH-VECTOR TLV MUST be ordered.
When sending a PCEP message (PCRpt, PCUpd, or PCInitiate), a PCEP
Speaker MAY add the PCEP-PATH-VECTOR TLV with a PCEP-SPEAKER-
INFORMATION containing its own information. If the PCEP message sent
is the result of a previously received PCEP message, and if the PCEP-
PATH-VECTOR TLV was already present in the initial message, the PCEP
speaker MAY append a new PCEP-SPEAKER-INFORMATION containing its own
information.
7. Security Considerations
The security considerations described in [RFC8231] and [RFC5440]
apply to the extensions described in this document as well.
Additional considerations related to state synchronization and sub-
delegation between stateful PCEs are introduced, as it could be
spoofed and could be used as an attack vector. An attacker could
attempt to create too much state in an attempt to load the PCEP peer.
The PCEP peer responds with a PCErr message as described in
[RFC8231]. An attacker could impact LSP operations by creating bogus
state. Further, state synchronization between stateful PCEs could
provide an adversary with the opportunity to eavesdrop on the
network. Thus, securing the PCEP session using Transport Layer
Security (TLS) [RFC8253], as per the recommendations and best current
practices in [RFC7525], is RECOMMENDED.
8. Acknowledgements
Thanks to [I-D.knodel-terminology] urging for better use of terms.
9. IANA Considerations
This document requests IANA actions to allocate code points for the
protocol elements defined in this document.
9.1. PCEP-Error Object
IANA is requested to allocate a new Error Value for the Error Type 9.
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Error-Type Meaning Reference
6 Mandatory Object Missing [RFC5440]
Error-value=TBD1: SPEAKER-IDENTITY-TLV This
missing document
24 LSP instantiation error [RFC8281]
Error-value=TBD5: No PCEP session with the This
headend document
9.2. PCEP TLV Type Indicators
IANA is requested to allocate new TLV Type Indicator values within
the "PCEP TLV Type Indicators" sub-registry of the PCEP Numbers
registry, as follows:
Value Meaning Reference
TBD2 ORIGINAL-LSP-DB-VERSION TLV This document
TBD3 PCEP-PATH-VECTOR TLV This document
9.3. STATEFUL-PCE-CAPABILITY TLV
IANA is requested to allocate a new bit value in the STATEFUL-PCE-
CAPABILITY TLV Flag Field sub-registry.
Bit Description Reference
TBD4 INTER-PCE-CAPABILITY This document
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
10.2. Informative References
[I-D.knodel-terminology]
Knodel, M. and N. Oever, "Terminology, Power, and
Inclusive Language in Internet-Drafts and RFCs", draft-
knodel-terminology-04 (work in progress), August 2020.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
DOI 10.17487/RFC6805, November 2012,
<https://www.rfc-editor.org/info/rfc6805>.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8751] Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
"Hierarchical Stateful Path Computation Element (PCE)",
RFC 8751, DOI 10.17487/RFC8751, March 2020,
<https://www.rfc-editor.org/info/rfc8751>.
[RFC8800] Litkowski, S., Sivabalan, S., Barth, C., and M. Negi,
"Path Computation Element Communication Protocol (PCEP)
Extension for Label Switched Path (LSP) Diversity
Constraint Signaling", RFC 8800, DOI 10.17487/RFC8800,
July 2020, <https://www.rfc-editor.org/info/rfc8800>.
Appendix A. Contributors
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Authors' Addresses
Stephane Litkowski
Cisco
Email: slitkows.ietf@gmail.com
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Siva Sivabalan
Ciena Corporation
Email: msiva282@gmail.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: c.l@huawei.com
Haomian Zheng
Huawei Technologies
H1, Huawei Xiliu Beipo Village, Songshan Lake
Dongguan, Guangdong 523808
China
Email: zhenghaomian@huawei.com
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