Path Computation Element Working Group O. Dugeon
Internet-Draft J. Meuric
Intended status: Standards Track Orange
Expires: September 14, 2017 March 13, 2017
A Backward Recursive PCE-initiated inter-domain LSP Setup
draft-dugeon-brpc-stateful-00
Abstract
The Path Computation Element (PCE) working group (WG) has produced a
set of RFCs to standardize the behavior of the Path Computation
Element as a tool to help MPLS-TE, GMPLS LSP tunnels and Segment
Routing paths placement. This also include the ability to compute
inter-domain LSPs or Segment Routing path following a distributed or
hierarchical approach. In complement to the original stateless mode,
a stateful mode has been added. In particular, the new PCInitiate
message allows a PCE to directly ask a PCC to setup an MPLS-TE, GMPLS
LSP tunnels or a Segment Routing path. However, once computed, the
inter-domain LSPs or Segment Routing path are hard to setup in the
underlying network. Especially, in operational network, RSVP-TE
signaling is not enable between BGP border routers. But, such RSVP-
TE signaling is mandatory to setup contiguous LSP tunnels or to
stitch or nest independent LSP tunnels to form the end-to-end inter-
domain LSP tunnels. This draft propose to combine a Backward
Recursive method with PCInitiate message to setup independent LSP
tunnels per domain and stitch or nest the different LSP tunnels to
setup end-to-end inter-domain LSP tunnels without the need of inter-
domain signaling between BGP border routers. A new Stitching Label
definition and new LSP-TYPE code points are proposed for that
purpose.
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 RFC 2119 [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/.
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Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
1.1. General assumptions . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Stitching Label . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Inter-domain LSP-TYPE . . . . . . . . . . . . . . . . . . 7
3. Inter-domain LSP tunnels setup procedure . . . . . . . . . . 8
3.1. Mode of operation . . . . . . . . . . . . . . . . . . . . 8
3.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Inter-domain LSP setup procedure completion failure . . . 11
3.4. Inter-domain LSP management . . . . . . . . . . . . . . . 12
4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 13
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5.1. LSP-TYPE values . . . . . . . . . . . . . . . . . . . . . 13
5.2. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Problem Statement
Looking to the different RFCs that describe the PCE architecture and
in particular PCE based architecture [RFC4655], PCE protocol
[RFC5440], BRPC [RFC5441] and H-PCE [RFC6805], the Path Computation
Element (PCE) is able to compute inter-domain path in complement to
intra-domain computation. Such inter-domain paths could then serve
as the Explicit Route Object input for the RSVP-TE signaling to setup
the LSPs tunnel within the underlying network. Three sort of end-to-
end LSP tunnels could be established:
o Contiguous tunnels: The RSVP-TE signaling crosses the boundary
between two domains e.g. between two AS Border Routers (ASBR) like
if it is two routers of the same domain. This kind of tunnel is
not recommended mostly for security and scalability purpose. In
addition, the initiating domain imposes huge constraints on
subsequent domains, because they undergo the tunnel request
without being able to control it.
o Stitching tunnels: Each domain establishes in its own network the
corresponding part of the end-to-end LSP tunnel independently.
Then, a second end-to-end RSVP-TE Path message is sent by the
initiating domain to stitch the different tunnel parts to form the
end-to-end LSP tunnel. In fact, this second RSVP-TE Path message
is used by border nodes to exchange the label that must be used by
the previous domain to send the traffic in order that the IP
packets follow the next LSP tunnel in the following domain. These
labels are convey in the RSVP-TE Resv message.
o Nesting tunnels: This is similar to the stitching mode but, this
time, with the possibility to setup tunnel hierarchy. For
example, an LSP tunnel between two edge domains crossing a transit
domain could be inserted into a tunnel of higher hierarchy in the
transit domain. Again, a second end-to-end RSVP-TE Path message
is sent from the source to the destination. Labels that must be
used to nest local tunnels are carried by the RSVP-TE Resv
message.
In all case, RSVP-TE signaling must be exchange between the different
domains. However, from an operational point of view, looking to
different networks under the responsibility of different
administrative entities, only BGP protocol are setup and configured
between AS Border Routers (ASBR). Indeed, to the author's knowledge,
there is no example of operational networks that enable RSVP-TE
between ASBR. Technology speaking, this is possible and many RFCs
describe how to use RSVP-TE at the inter-domain. But, due to
security, scalability, management and contract constraints, RSVP-TE
is no longer exposed at the network boundary. To circumvent the
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security issue, RSVP-TE could be carry inside an IPsec tunnel between
ASBR, but, this not eliminate the scalability aspect nor the
constraints impose by seting up and end-to-end LSP tunnels.
The purpose of this memo is to take the benefit of PCE stateful mode
as per draft pce stateful [I-D.ietf-pce-stateful-pce] and draft pce
initiated [I-D.ietf-pce-pce-initiated-lsp] to stitch or nest inter-
domain LSP tunnels directly using PCEP protocol between domain's PCE
instead of using RSVP-TE signaling at the inter-domain while keeping
each operator independently setup their respective part of the end-
to-end LSP tunnels. PCInitiated message is used in a Backward
Recursive way like the PCReq message in BRPC [RFC5441], to
recursively setup the end-to-end tunnel. PCRep message is used to
automatically stitch or nest the different local LSP tunnels. And,
PCRep in conjunction of PCUpd messages are used to maintain, modify
and remove end-to-end LSP tunnels.
1.1. General assumptions
In the rest of this document, we used the same references as per BRPC
[RFC5441] and make the following set of assumptions (see figure
below):
o Domain refers to an IGP area or an Autonomous System (AS).
o Inter-domain LSP tunnel is used to refer to an LSP tunnel that
cross two or more different domains as defined previously,
o At least, one PCE is deployed in each domain. These PCE are all
stateful active capable and could request to enforce LSP tunnels
in their respective domain by means of PCInitiate messages.
o LSRs, including border nodes, are PCC enable and support stateful
active mode. PCEP sessions is established between these routers
and their domain's PCE.
o Each PCE establishes a PCEP session with its respective neighbor
domain's PCE. The way a PCE discover its neighboring PCE is out
of scope of this draft. These information could be fulfill
administratively or automatically discovered through, for example
per draft 'BGP Extensions for Path Computation Element (PCE)
Discovery' [I-D.dong-pce-discovery-proto-bgp],
o PCEs are able to compute and end-o-end path as per BRPC procedure
[RFC5441].
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+----------------+ +----------------+
| Domain (B) | | Domain (C) |
| | | |
| /-------|---PCEP---|--------\ |
| / | | \ |
| [PCE-B] | | [PCE-C] |
| / (BN)<------>(BN) |
| / | Inter | |
+---|--(BN)------+ Domain +----------------+
| ^ Link
PCEP |
| | Inter-domain Link
| v
+---|--(BN)------+
| | |
| | Domain (A) |
| \ |
| [PCE-A] |
| |
| |
+----------------+
Example of the representation of 3 domains with 3 PCEs
1.2. Terminology
ABR: Area Border Routers. Routers used to connect two IGP areas
(areas in OSPF or levels in IS-IS).
ASBR: Autonomous System Border Router. Router used to connect
together ASes of the same or different service providers via one or
more inter-AS links.
AS: Autonomous System
Border Node (BN): a boundary node is either an ABR in the context of
inter-area Traffic Engineering or an ASBR in the context of inter-AS
Traffic Engineering.
Domains: Autonomous System (AS) or IGP Area. An Autonoumous System
is composed by one or more IGP area.
Entry BN of domain(i): a BN connecting domain(i-1) to domain(i) along
a determined sequence of domains. Multiple entry BN(i) could be used
to connect domain(i-1) to domain(i).
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Exit BN of domain(i): a BN connecting domain(i) to domain(i+1) along
a determined sequence of domains. Multiple exit BN(i) could be used
to connect domain(i) to domain(i+1).
Inter-domain LSP tunnel: A LSP tunnel that crosses two or more
domains through a per of Border Node.
Local LSP tunnel: A LSP tunnel that do not cross a domain. It is
setup between entry BN to exit BN, any source to exit BN or entry BN
to any destination of the same domain.
Local LSP tunnel(i): A local LSP tunnel of domain(i)
IGP-TE: Interior Gateway Protocol with Traffic Engineering support.
Both OSPF-TE and IS-IS-TE are identified in this category.
Stitching Label (SL): A dedicated label that is used to stitch two
RSVP-TE tunnels or two Segment Routing paths.
PCE: Path Computation Element. An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.
PCE(i) is a PCE with the scope of domain(i).
2. Stitching Label
This section introduce the concept of Stitching Label that allows
stitching and nesting of Local LSP tunnels in order to form inter-
domain LSP tunnel that cross several different domains.
2.1. Definition
The operation of stitch or nest a local LSP tunnel(i) to a local LSP
tunnel(i+1) in order to form and inter-domain LSP tunnel simply
consist in defining the label that the exit BN(i) will use to send
its traffic to the entry BN(i+1). Indeed, the entry BN(i+1) needs to
identify the incoming traffic i.e. IP packets, in order to know if
this traffic must follow the local LSP tunnel(i+1) or not.
Forwarding Equivalent Class (FEC) could be used for that purpose.
But, when stitching or nesting tunnels, the FEC is reduce to the
incoming label that the entry BN(i+1) as chosen for the local LSP
tunnel(i+1).
In this memo, we introduce the named of 'Stitching Label (SL)' to
designate this label. Such label is usually exchange between exit
BN(i) and entry BN(i+1) with the RSVP-TE signaling. But, as we want
to avoid to use RSVP-TE signaling due to operational constraints,
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this Stitching Label will be convey by PCEP protocol. In fact, the
Explicit Route Object (ERO) and the Record Route Object (RRO) are
defined in order to transport this Stitching Label in the RSVP-TE
signaling. As PCEP protocol used RSVP-TE Objects, and in particular
the ERO and ERO, it is able to convey the Stitching Label without any
modification of the PCEP protocol nor the PCE or RSVP-TE Objects.
As per RFC4003 [RFC4003], the Stitching Label will be convey as a
companion of an IP address. In our case, this is the IP address of
the input interface ITF_INPUT(i+1) of BN(i+1) which is connected to
the exit BN(i) and which receives the traffic from the domain(i).
2.2. Inter-domain LSP-TYPE
However, even if PCEP could convey the Stitching Label, a PCC is not
aware that a PCE requests or provides such label. For that purpose,
this memo propose to use the LSP-TYPE as defined in draft lsp setup
type [I-D.ietf-pce-lsp-setup-type] with new values (See IANA section
of this memo) defined as follow:
o TBD1: Inter-Domain Traffic engineering end-to-end path is setup
using Backward Recursive method. This new LSP-TYPE value MUST be
set in a PCInitiate messages sends by a PCE(i) to its neighbor
PCE(i+1) to initiate a new inter-domain LSP tunnel. In turn,
neighbor PCE(i+1) MUST return a Stitching Label SL with the IP
address of the associated interface in the RRO of the PCRpt
message to PCE (i).
o TBD2: Inter-Domain Traffic engineering local path is setup using
RSVP-TE. This new LSP-TYPE value MUST be set in the PCInitiate
message sends by a PCE(i) requesting to a PCC of domain(i) to
initiate a new local LSP tunnel(i) which is part of an inter-
domain LSP tunnel. This LSP-TYPE value MUST be used by the PCE(i)
only after receiving a PCInitiate message with an LSP-TYPE equal
to TBD1 from a neighbor PCE(i-1). In turn, the PCC of domain(i)
MUST return a Stitching Label SL with the IP address of associated
interface in the RRO of the PCRpt message.
o TBD3: Inter-Domain Traffic engineering local path is setup using
Segment Routing. This new LSP-TYPE value MUST be set in the
PCInitiate message sends by a PCE(i) requesting to a PCC of
domain(i) to initiate a new Segment Routing path which is part of
and inter-domain Segment Routing path. This LSP-TYPE value MUST
be used by the PCE(i) only after receiving a PCInitiate message
with an LSP-TYPE equal to TBD1 from a neighbor PCE(i-1). In turn,
the PCC MUST return a Stitching Label SL with the IP address of
the associated interface in the RRO of the PCRpt message.
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3. Inter-domain LSP tunnels setup procedure
This section describes how to setup inter-domain LSP tunnels than
cross several different domains.
3.1. Mode of operation
This section describes how PCInitiate and PCRpt messages are combined
between PCE in order to setup inter-domain LSP tunnels between a
source domain(1) to a destination domain(n). S and D are
respectively the source and destination of the inter-domain LSP
tunnel. Domain(1) and domain(n) are different and connected through
0 or more intermediate domains denoted domain(i) with i = (2, n-1).
Domains are directly connected when n = 2.
First, the PCE(S) run standard BRPC algorithm as per RFC5441
[RFC5441] with its neighbor PCEs in order to compute the inter-domain
LSP tunnel from S to D, where S and D are respectively a node in the
domain(1) and domain(n). Path Key confidentiality as per RFC5520
[RFC5520] MAY be used to obfuscate the detailed ERO of the different
domains(i). The resulting ERO is of the form (S, PKS(1), exit BN(1),
..., entry BN(i), PKS(i), exit BN(i), ..., entry BN(n), PKS(n), D).
As subsequent domains are not aware about the final computed ERO in
case of multiple VSPT, the final computed ERO MUST be send in the
PCInitiate message to indicate to the subsequent PCEs which solution
has been finally chosen.
The complete procedure follow the different steps described below:
Steps 1: Initialization
Once ERO(S, D) computed, PCE(1) sends a PCInitiate message to PCE(2)
containing and ERO equal to {S, PKS(1), exit BN(1), ..., entry BN(i),
PKS(i), exit BN(i), ..., entry BN(n), PKS(n), D}, LSP-TYPE = TBD1 and
End-Points Object = (S, D). The ERO corresponds to the one PCE(1) as
received from PCE(2) during the BRPC process. In case of multiple
EROs, i.e. VSPT > 1, PCE(1) has chosen one of them and used the
selected one for the PCInitiate message. PKS(i) could be replaced by
the full ERO description if Path Key is not used by PCE(i).
When PCE(i) receives a PCInitiate message from domain(i-1) with LSP-
TYPE = TBD1 and ERO = {entry BN(i), PKS(i), exit BN(i), ..., entry
BN(n), PKS(n), D)}, it forwards the PCInitiate message to PCE(i+1)
once remove its {entry BN(i), PKS(i), exit BN(i)} part from the ERO.
All intermediate PCE(i) propagate the PCInitiate message to PCE(i+1)
up to the domain(n).
Steps 2: Actions taken at the destination domain(n)
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When PCInitiate message propagation reach the destination domain(n),
PCE(n) retrieves the ERO from the PKS(n) if necessary and sends to
entry BN(n) a PCInitiate message with the ERO(n) = {BN(n), ..., D},
LSP-TYPE= TBD2 and End-Points Object = (BN(n), D) in order to inform
the PCC BN(n) that this local LSP tunnel(n) is part of an inter-
domain LSP tunnel. When the PCC entry BN(n) received the PCInitiate
message from its PCE(n), it setup the LSP tunnels from entry BN(n) to
D by means of RSVP-TE signaling with the given ERO(n). Once the
tunnel setup, it chooses a free label for the Stitching Label SL(n)
and add a new entry in its MPLS LFIB with this SL(n) label. Then, it
sends a PCRpt message to its PCE(n) with an RRO equal to
{[ITF_INPUT(n), SL(n)], RRO(n)}. Once PCE(n) receives the PCRpt from
the PCC BN(n) with the RRO and LSP-TYPE = TBD2, it sends to the
PCE(n-1) a PCRpt containing the RRO equal to {[ITF_INPUT(n), SL(n)]}.
PCE(n) MAY adds BN(n), D in the RRO as loose path.
Steps i: Actions performed by all intermediate domains(i), for i = 2
to n-1
1. When the PCE(i) receives a PCRpt message from domain(i+1) with
LSP-TYPE = TBD1 and RRO = {[ITF_INPUT(i+1), SL(i+1)]}, it
retrieves the ERO from the PKS(i) if necessary and sends to the
PCC entry BN(i) a PCInitiate message with ERO = {ERO(i),
[ITF_INPUT(i+1), SL(i+1)]}, LSP-TYPE = TBD2 and End-Points Object
= {entry BN(i), exit BN(i)} in order to inform the PCC entry
BN(i) that this local LSP tunnel(i) is part of an inter-domain
LSP tunnel.
2. When the PCC entry BN(i) received the PCInitiate message from its
PCE(i), it setup the LSP tunnels from entry BN(i) to exit BN(i)
by means of RSVP-TE signaling with the given ERO(i).
3. When the exit Bn(i) receives an RSVP-TE Path message with an ERO
= {x-1, [ITF_INPUT(i+1), SL(i+1)]} and End-Points Object = {entry
BN(i), exit BN(i)}, it MUST install in its MPLS LFIB the SWAP
instruction to label SL(i+1) with forward to ITF_INPUT(i+1)
instead of the standard POP instruction.
4. Once the tunnel setup, it chooses a free label for the Stitching
Label SL(i) and add a new entry in its MPLS LFIB with this SL(i)
label. Then, it sends a PCRpt message to its PCE(i) with an RRO
equal to {[ITF_INPUT(i), SL(i)], RRO(i)}.
5. Once PCE(i) receives the PCRpt from the PCC entry BN(i) with the
RRO and LSP-TYPE = TBD2, it sends to the PCE(i-1) a PCRpt
containing the RRO equal to {[ITF_INPUT(i), SL(i)]}. PCE(i) MAY
adds entry BN(i), exit BN(i) in the RRO as loose path.
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Steps n: Actions performed at the source domain(1)
Once PCE(1) received the PCRpt message from PCE(2) with the RRO
containing the label SL(2), it sends a PCInitiate message to PCC node
S with ERO equal to {ERO(1), [ITF_INPUT(2), SL(2)]}, LSP_TYPE = 0 and
End-Points Object = {S, BN(1)}. This time, the LSP_TYPE is equal to 0
as the PCC S does not need to return a Stitching Label SL i.e. it is
the head-end of the inter-domain LSP tunnel. Standard PCRpt message
is sent back to PCE(1) by the PCC node S.
To use Segment Routing instead of RSVP-TE to setup the LSP tunnels as
defined in draft pce segment routing [I-D.ietf-pce-segment-routing],
PCEs MUST send PCInitiate message with LSP-TYPE = TBD3 instead of
TBD2 to advertise their respective PCC that the LSP tunnels is
enforce by means of Segment Routing. SL label will be inserted in
the label stack in order to become the top label in the stack when
the packet reach entry BN(i+). Then, entry BN(i+1) will push a new
label stack to reach the exit BN(i+1) and follow.
3.2. Example
In the figure below, two different domains S and D are interconnected
through BN respectively BN-S and BN-D. PE-S and PE-D are edge
routers. All routers in the figure are connected to their respective
PCE through PCEP protocol. In this example, PCE(S) would setup an
intre-domain LSP tunnel between PE-S and PE-D acting as source and
destination of the tunnel. Intermediate routers between (PE-S, BN-
S), (BN-D and PE-D) as well as RSVP-TE messages are not represented
to simplify the figure. But they are all presents. The following
notation is used in the figure:
o PKS(D) = Path Key correponding to the path from BN(D) to PE-D
o ERO(D) = Explicit Route Object corresponding to the path from
BN(D) to PE-D retrieves from PKS(D)
o RRO(D) = Record Route Object of Local LSP tunnel(D) from BN(D) to
PE-D
o SL(D) = Stitching Label for Local LSP tunnel from BN(D) to PE-D
o ERO(S) = Explicit Route Object corresponding to the path from PE-S
to BN(S)
o RRO(S) = Record Route Object of Local LSP tunnel(S) from PE-S to
BN(S)
1.
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PE-S PCE-S BN-D PCE-D
| | | |
| [ -------- Standard BRPC exchange ------------]
| | | |
| | PCInitiate(ERO={BN(D), PKS(D)}, LSP-TYPE = TBD1)
| | --------------------------------------> |
| | | |
| | PCInitiate(ERO = ERO(D), LSP-TYPE = TBD2)
| | | <------- |
| | | |
| | PCRpt(RRO = {SL(D), RRO(D)}, LSP-TYPE = TBD2)
| | | ------> |
| | | |
| | PCRpt(RRO = {SL(D), PKS(D)}, LSP-TYPE = TBD1)
| | <-------------------------------------- |
| | | |
| PCInitiate(ERO={ERO(S), SL(D), BN(D)}, LSP-TYPE = 0)
| <------- | | |
| | | |
| PCRpt(RRO={RRO(S)}, LSP-TYPE = 0) | |
| -------> | | |
| | | |
+----------------------+ +----------------------+
| | | |
| +------+ | PCEP | +------+ |
| +---->|PCE(S)|<-------------------------------->|PCE(D)| |
| | +------+ | | +------+ |
| | ^ | | ^ ^ |
| | | | | | | |
| |PCEP | | | | | |
| | |PCEP | | PCEP | | PCEP |
| v | | | | | |
(PE-S) +------> (BN-S) <---------> (BN-D)<----+ +----> (PE-D)
| | Inter-Domain | |
| Domain (S) | Link | Domain (D) |
+----------------------+ +----------------------+
[--- LSP Tunnel (S) ---][---- SL label ----][--- LSP Tunnel (D) ---]
Example of end-to-end LSP tunnel setup between two domains
3.3. Inter-domain LSP setup procedure completion failure
In case of error during LSP setup, PCRpt and or PCError messages MUST
be used to signal the problem to the neighbor PCE domain backward.
In particular, if new LSP-TYPE values defined in this memo are not
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supported by the neighbor PCE or the PCC, the PCE, receptively the
PCC, MUST return a PCErr message with Error-Type = 21 (Traffic
engineering path setup error) and Error-Value = 1 (Unsupported path
setup type) to its neighbor PCE.
If a PCC or a PCE don't return an RRO or an RRO without the Stitching
Label SL with the IP address of the associated interface following a
PCInitiate message with LSP-TYPE set to the new values defined in
this memo, the PCE MUST return a PCErr message with Error-Type = 21
(Traffic engineering path setup error) and Error-Value = TBD4 (No
Mandatory Stitching Label is present in the RRO).
In case of completion failure, the PCE(i) MUST propagate the PCErr
message up to the PCE(1). In turn, PCE(1) MUST send a PCInitate
message (R flag set in the SRP Object as per draft pce initiated lsp
[I-D.ietf-pce-pce-initiated-lsp] to delete this inter-domain LSP
tunnel to its neighbor PCEs. PCE(i) MUST propagate the PCInitiate
message and remove their Local LSP tunnel by means of PCInitiate
message to their PCC entry BN(i) and send back PCRpt message to
PCE(i-1).
3.4. Inter-domain LSP management
Each domain manages their respective local LSP tunnel part of an
inter-domain LSP tunnel independently of each other. In particular,
Stitching Label(i) is managed by domain(i) and is of interest of
domain(i-1) only. Thus, Stitching Label SL(i) is not supposed to be
propagated to other domains.
If a PCE(i) needs to modify its local LSP tunnel(i) with PCUpd
message, it MUST sends a new PCRpt message to its neighbor PCE(i-1)
to advertise it of the modification, in particular if this concern a
modification of Stitching Label SL(i).
PCE(1) could modify the inter-domain LSP tunnel. For that purpose,
it MUST sends a PCUpd message to its neighbor PCEs. Each PCE(i) MUST
process PCUpd message the same way they process PCInitiate message:
first, propagate the PCUpd message up to the destination domain(n),
then process the modification once PCRpt received from PCE(i+1) and
send PCRpt to PCE(i-1) once modification done.
Modification of Local LSP tunnel, entry BN(i) and exit BN(i) is left
for further study.
In case of a failure appear in domain(i), PCE(i) MUST sends a PCRpt
message to its neighbor PCE(i-1) to advertise it that its local part
of the inter-domain LSP tunnel is down. Once PCE(1) receives this
PCRpt message indicating that the tunnel is down, it is up to the
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PCE(1) to take appropriate correction e.g. start a new BRPC to
compute a new ERO.
4. Applicability
The newly introduce Stitching Label SL serves to stitch or nest part
of LSP tunnels to form an inter-domain LSP tunnel. Each domain is
free to decide if the tunnel is stitched or nested. For example, a
domain(i) may decided to nest the incoming Local LSP tunnel into a
higher hierarchy of tunnel for Traffic Engineering purpose. A PCE(i)
may also decided to group Local LSP tunnels part of inter-domain LSP
tunnels into a higher hierarchical tunnel to carry all these Local
LSP tunnels from one entry BN(i) to one exit BN(i).
The Stitching Label SL could serves to stitch Segment Path and RSVP-
TE tunnel. Indeed, each domain is free to enforce its part of the
inter-domain LSP tunnel with the underlying mechanism it chosen.
Stitching Label SL will be part of the label stack in order to become
the top label in the stack when reaching the entry BN(i+1). This
Stitching Label could be swap as usual if the next domain that uses
RSVP-TE tunnel. When the previous domain uses a RSVP-TE tunnel, the
Stitching Label will serve as key for the entry BN(i+1) to determine
which label stack it must push on top of the packet for a Segment
Routing path.
In inter-layer scenario is left for further study.
5. IANA Considerations
5.1. LSP-TYPE values
Draft pce lsp setup type [I-D.ietf-pce-lsp-setup-type] defines the
PATH-SETUP-TYPE TLV and requests that IANA creates a registry to
manage the value of the PATH_SETUP_TYPE TLV's PST field. IANA is
requested to allocate a new code point in the PCEP PATH_SETUP_TYPE
TLV PST field registry, as follows:
+-------+-----------------------------------------------+-----------+
| Value | Description | Reference |
+-------+-----------------------------------------------+-----------+
| TBD1 | Inter-Domain Traffic engineering end-to-end | This |
| | path is setup using Backward Recursive method | Document |
| TBD2 | Inter-Domain Traffic engineering local path | This |
| | is setup using RSVP-TE | Document |
| TBD3 | Inter-Domain Traffic engineering local path | This |
| | is setup using Segment Routing | Document |
+-------+-----------------------------------------------+-----------+
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5.2. PCEP-Error Object
IANA is requested to allocate code-points in the PCEP-ERROR Object
Error Values registry for a new error-value or Error-Type 21 Invalid
traffic engineering path setup:
+-------------+------------------------------------------+
| Error-Value | Description |
+-------------+------------------------------------------+
| TBD4 | Missing Mandatory Stitching Label in RRO |
+-------------+------------------------------------------+
6. Security Considerations
No modification of PCE protocol (PCEP) has been requested by this
draft which not introduce any issue regarding security. Concerning
the PCEP session between PCEs, authors recommend to use the secure
version of PCEP as defined in draft secure transport for PCEP
[I-D.ietf-pce-pceps] or use any other secure tunnel mechanism e.g.
IPsec tunnel to transport PCEP session between PCE.
7. Acknowledgements
The authors want to thanks PCE's WG members.
8. References
8.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<http://www.rfc-editor.org/info/rfc4655>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://www.rfc-editor.org/info/rfc5440>.
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[RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
"A Backward-Recursive PCE-Based Computation (BRPC)
Procedure to Compute Shortest Constrained Inter-Domain
Traffic Engineering Label Switched Paths", RFC 5441,
DOI 10.17487/RFC5441, April 2009,
<http://www.rfc-editor.org/info/rfc5441>.
8.2. Informative References
[I-D.dong-pce-discovery-proto-bgp]
Dong, J., Chen, M., Dhody, D., Tantsura, J., Kumaki, K.,
and T. Murai, "BGP Extensions for Path Computation Element
(PCE) Discovery", draft-dong-pce-discovery-proto-bgp-06
(work in progress), October 2016.
[I-D.ietf-pce-lsp-setup-type]
Sivabalan, S., Medved, J., Minei, I., Crabbe, E., Varga,
R., Tantsura, J., and J. Hardwick, "Conveying path setup
type in PCEP messages", draft-ietf-pce-lsp-setup-type-03
(work in progress), June 2015.
[I-D.ietf-pce-pce-initiated-lsp]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", draft-ietf-pce-pce-initiated-lsp-09 (work in
progress), March 2017.
[I-D.ietf-pce-pceps]
Lopez, D., Dios, O., Wu, W., and D. Dhody, "Secure
Transport for PCEP", draft-ietf-pce-pceps-11 (work in
progress), January 2017.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and
J. Hardwick, "PCEP Extensions for Segment Routing", draft-
ietf-pce-segment-routing-08 (work in progress), October
2016.
[I-D.ietf-pce-stateful-pce]
Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-
pce-18 (work in progress), December 2016.
[RFC4003] Berger, L., "GMPLS Signaling Procedure for Egress
Control", RFC 4003, DOI 10.17487/RFC4003, February 2005,
<http://www.rfc-editor.org/info/rfc4003>.
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[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Path-Key-Based Mechanism", RFC 5520,
DOI 10.17487/RFC5520, April 2009,
<http://www.rfc-editor.org/info/rfc5520>.
[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,
<http://www.rfc-editor.org/info/rfc6805>.
Authors' Addresses
Olivier Dugeon
Orange
2, Avenue Pierre Marzin
Lannion 22307
France
Email: olivier.dugeon@orange.com
Julien Meuric
Orange
2, Avenue Pierre Marzin
Lannion 22307
France
Email: julien.meuric@orange.com
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