| Path Computation Element Working Group | O. Dugeon |
| Internet-Draft | J. Meuric |
| Intended status: Standards Track | Orange Labs |
| Expires: January 3, 2019 | Y. Lee |
| D. Dhody | |
| Huawei Technologies | |
| D. Ceccarelli | |
| Ericsson | |
| July 02, 2018 |
PCEP Extension for Stateful Inter-Domain Tunnels
draft-dugeon-pce-stateful-interdomain-01
This document proposes to combine a Backward Recursive or Hierarchical method in Stateful PCE with PCInitiate message to setup independent paths per domain, and combine these different paths together in order to operate them as end-to-end inter-domain paths without the need of signaling session between AS border routers. A new Stitching Label is defined and new LSP-TYPE code points are considered for that purpose.
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.
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 https://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."
This Internet-Draft will expire on January 3, 2019.
Copyright (c) 2018 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 (https://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.
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 includes the ability to compute inter-domain LSPs or Segment Routing paths following a distributed or hierarchical approach. To complement 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 tunnel 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 enabled between AS 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 paths.
Looking to the different RFCs that describe the PCE architecture and in particular PCE based architecture, PCE protocol, BRPC and H-PCE, the Path Computation Element (PCE) is able to compute inter-domain paths 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 tunnels within the underlying network. Three kinds of inter-domain paths could be established:
In all case, RSVP-TE signaling must be exchanged between the different domains. However, from an operational point of view, looking to different networks under the responsibility of different administrative entities, only BGP sessions are setup and configured between ASBRs. Technologically speaking, this is possible and many RFCs describe how to use RSVP-TE for inter-domain. But, due to security, scalability, management and contract constraints, RSVP-TE is not exposed at the network boundary. To circumvent some of the security issues, RSVP-TE can be carried inside an IPsec tunnel between ASBRs, but, this does not eliminate the scalability aspect nor the constraints imposed by setting up inter-domain paths.
The purpose of this memo is to take the benefit of PCE Stateful and PCE Initiated modes to stitch or nest inter-domain paths directly using PCEP between domains' PCEs instead of using RSVP-TE signaling at the inter-domain border nodes, while keeping each operator free to independently setup their respective part of the inter-domain paths. PCInitiate message is used in a Backward Recursive way like the PCReq message in BRPC, 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 inter-domain paths. This method is also applicable to Segment Routing to build inter-domain segment paths.
H-PCE describes a Hierarchical PCE architecture which can be used for computing end-to-end paths for inter-domain MPLS Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs). Within this architecture, the Parent PCE (P-PCE) is used to compute a multi-domain path based on the domain connectivity information. A Child PCE (C-PCE) may be responsible for a single domain or multiple domains, it is used to compute the intra-domain path based on its domain topology information.
Stateful H-PCE presents general considerations for stateful PCE(s) in hierarchical PCE architecture. In particular, the behavior changes and additions to the existing stateful PCE mechanisms (including PCE-initiated LSP setup and active PCE usage) in the context of networks using the H-PCE architecture. Section 3.3.1describes the per domain stitched LSP mode, where the individual per domain LSP are stitched together. PCInitiate message is also used to stitch the end-to-end tunnel. See section 4 for details.
In the rest of this document, we used the same references as per BRPC and make the following set of assumptions (see figure below):
+----------------+ +----------------+
| 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
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 Autonomous System is composed by one or more IGP area.
BN-en(i): Entry BN of domain(i) connecting domain(i-1) to domain(i) along a determined sequence of domains. Multiple entry BN-en(i) could be used to connect domain(i-1) to domain(i).
BN-ex(i): Exit BN of domain(i) connecting domain(i) to domain(i+1) along a determined sequence of domains. Multiple exit BN-ex(i) could be used to connect domain(i) to domain(i+1).
Inter-domain path: A path that crosses two or more domains through a pair of Border Node (BN-ex, BN-en).
Local LSP tunnel: A LSP tunnel that do not cross a domain. It is setup between entry BN-en to output BN-ex, any source to output BN-ex or entry BN-en to any destination of the same domain. This LSP could be enforce by means of RSVP-TE signaling or Segment Routing labels stack.
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.
SL(i): A Stitching Label that link domain(i-1) to domain(i).
LK(i): A Link that connect BN-ex(i-1) to BN-en(i). Note that BN-ex(i-1) could be connected to BN-en(i) by more than one link. LK(i) serves to identify which of the multiple links will be used for the inter-domain LSP setup.
PLSP-ID(i): A PLSP-ID that identify the local tunnel part of an inter-domain tunnel in the domain(i).
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).
This section introduce the concept of Stitching Label that allows stitching and nesting of local LSP tunnels in order to form inter-domain path that cross several different domains.
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 path simply consist in defining the label that the output BN-ex(i) will use to send its traffic to the entry BN-en(i+1). Indeed, the entry BN-en(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-en(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 output BN-ex(i) and entry BN-en(i+1) with the RSVP-TE signaling. But, as we want to avoid to use RSVP-TE signaling due to operational constraints, 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 RRO, 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, the Stitching Label will be convey as a companion of an IP address. In our case, this is one of the IP address of the link LK(i) which connects BN-ex(i) to BN-en(i+1) and carries the traffic from the domain(i) to domain(i+1). It is left to implementation to select which of the two IP address of the link LK(i) is used.
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 [I-D.ietf-pce-lsp-setup-type] with new values (See IANA section of this memo) defined as follow:
This section describes how to setup inter-domain paths than cross several different domains by using a Backward Recursive method which is compatible to inter-domain path computation by means of the BRPC procedure as describe in RFC5441.
This section describes how PCInitiate and PCRpt messages are combined between PCE in order to setup inter-domain paths between a source domain(1) to a destination domain(n). S and D are respectively the source and destination of the inter-domain path. 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 with its neighbor PCEs in order to compute the inter-domain path 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 MAY be used to obfuscate the detailed ERO of the different domains(i). The resulting ERO is of the form {S, PKS(1), BN-ex(1), ..., BN-en(i), PKS(i), BN-ex(i), ..., BN-en(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), BN-ex(1), ..., BN-en(i), PKS(i), BN-ex(i), ..., BN-en(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 = {BN-en(i), PKS(i), BN-ex(i), ..., BN-en(n), PKS(n), D)}, it forwards the PCInitiate message to PCE(i+1) once remove its {BN-en(i), PKS(i), BN-ex(i)} part from the ERO. All PCE(i) propagate the PCInitiate message to PCE(i+1) up to PCE(n) i.e. to the domain(n).
Steps 2: Actions taken at the destination domain(n) by PCE(n)
When PCInitiate message propagation reach the destination domain(n), PCE(n) retrieves the ERO from the PKS(n) if necessary and sends to BN-en(n) a PCInitiate message with the ERO(n) = {BN-en(n), ..., D}, LSP-TYPE= TBD2 and End-Points Object = {BN(n), D} in order to inform the PCC BN-en(n) that this local LSP tunnel(n) is part of an inter-domain path. When the PCC BN-en(n) received the PCInitiate message from its PCE(n), it setup the local LSP tunnels from entry BN-en(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 {[LK(n), SL(n)], RRO(n)} and PLSP-ID(n). Once PCE(n) receives the PCRpt from the PCC BN-en(n) with the RRO, PLSP-ID and LSP-TYPE = TBD2, it sends to the PCE(n-1) a PCRpt containing the RRO equal to {[LK(n), SL(n)]} and PLSP-ID(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
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), [LK(2), SL(2)]}, LSP_TYPE = 0 and End-Points Object = {S, BN-ex(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 path. Standard PCRpt message is sent back to PCE(1) by the PCC node S.
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 inter-domain path 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:
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, PLSP-ID(D))
| | <-------------------------------------- |
| | | |
| 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 inter-domain path setup between two domains
In case of error during LSP setup, PCRpt and or PCErr 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 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 PCE(i) receives a PCInitiate message from its peer PCE(i-1) without LSP-TYPE set to TBD1 or LSP-TYPE set to a value different from TBD1, it MUST return a PCErr message with Error-Type = 21 (Traffic engineering path setup error) and Error-Value = 1 (Unsupported path setup type) to its peer PCE(i-1).
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 link following a PCInitiate message with LSP-TYPE set to TBD1, 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) to delete this inter-domain path 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 BN-en(i) and send back PCRpt message to PCE(i-1).
In case of error in domain(i+1), PCE(i) MAY add the AS number of domain(i+1) in the RRO to identify the faulty domain.
This section describes how to setup inter-domain paths than cross several different domains by using a Hierarchical method which is compatible to inter-domain path computation as describe in [RFC6805].
This section describes how PCInitiate and PCRpt messages are combined between PCE in order to setup inter-domain paths between a source domain(1) to a destination domain(n). S and D are respectively the source and destination of the inter-domain path. 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 Parent PCE contacts its Child PCE as per [RFC6805] in order to compute the inter-domain path 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 MAY be used to obfuscate the detailed ERO of the different domains(i). The resulting ERO is of the form (S, PKS(1), BN-ex(1), ..., BN-en(i), PKS(i), BN-ex(i), ..., BN-en(n), PKS(n), D).
The complete procedure follow the different steps described below:
Step 1: Initialization
Parent PCE sends a PCInitiate message to child PCE(n) with an ERO = {PKS(n)} and End-Points = {BN-en(n), D}. Then, PCE(n) retrieves the ERO from the PKS(n) if necessary and sends to BN-en(n) a PCInitiate message with the ERO(n) = {BN-en(n), ..., D}, LSP-TYPE= TBD2 and End-Points Object = {BN-en(n), D} in order to inform the PCC BN-en(n) that this local LSP tunnel(n) is part of an inter-domain path. When the PCC BN-en(n) received the PCInitiate message from its PCE(n), it setup the local LSP tunnel from entry BN-en(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 {[LK(n), SL(n)], RRO(n)} and PLSP-ID(n). Once PCE(n) receives the PCRpt from the PCC BN-en(n) with the RRO, PLSP-ID and LSP-TYPE = TBD2, it sends to its Parent PCE a PCRpt containing the RRO equal to {[LK(n), SL(n)]} and PLSP-ID(n). PCE(n) MAY adds {BN-en(n), D} in the RRO as loose path.
Steps i: Actions performed for all intermediate domains(i), for i = n-1 to 2
Steps n: Actions performed to the source domain(1)
Finally, Parent PCE sends a last PCInitiate message to Child PCE(1) with LSP-TYPE = TBD1, ERO = {PKS(1), [LK(2), SL(2)]} and End-Points = {S, BN-ex(1)}. In turn, Child PCE(1) sends a PCInitiate message to PCC node S with ERO equal to {ERO(1), [LK(2), SL(2)]}, LSP_TYPE = 0 and End-Points Object = {S, BN-ex(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 path. Standard PCRpt message is sent back to PCE(1) by the PCC node S. In turn, Child PCE(1) send a final PCRpt message to the Parent PCE with the PSLP-ID(1). PCE(1) MAY adds {S, BN-ex(1)} in the RRO as loose path.
In case of error during LSP setup, PCRpt and or PCError messages MUST be used to signal the problem to the Parent PCE. In particular, if new LSP-TYPE values defined in this memo are not supported by the Child PCE or the PCC, the Child 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 Parent PCE. If Child PCE(i) receives a PCInitiate message from its Parent PCE without LSP-TYPE set to TBD1 or LSP-TYPE set to a value different from TBD1, it MUST return a PCErr message with Error-Type = 21 (Traffic engineering path setup error) and Error-Value = 1 (Unsupported path setup type) to its Parent PCE.
If a Child PCE or a PCC don't return an RRO or an RRO without the Stitching Label SL with the IP address of the associated link following a PCInitiate message with LSP-TYPE set to TBD1, the Parent PCE, respectively the Child 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 Parent PCE MUST MUST send a PCInitate message (R flag set in the SRP Object as per draft pce initiated lsp) to delete this inter-domain path to the Child PCEs that already setup their respective part of the inter-domain tunnel. Child PCE(i) MUST remove their local LSP tunnel by means of PCInitiate message with R flag set to 1 to their PCC BN-en(i) and send back PCRpt message to the Parent PCE.
Taking the sample hierarchical domain topology example from [RFC6805] as the reference topology for the entirety of this section.
-----------------------------------------------------------------
| Domain 5 |
| ----- |
| |PCE 5| |
| ----- |
| |
| ---------------- ---------------- ---------------- |
| | Domain 1 | | Domain 2 | | Domain 3 | |
| | | | | | | |
| | ----- | | ----- | | ----- | |
| | |PCE 1| | | |PCE 2| | | |PCE 3| | |
| | ----- | | ----- | | ----- | |
| | | | | | | |
| | ----| |---- ----| |---- | |
| | |BN11+---+BN21| |BN23+---+BN31| | |
| | - ----| |---- ----| |---- - | |
| | |S| | | | | |D| | |
| | - ----| |---- ----| |---- - | |
| | |BN12+---+BN22| |BN24+---+BN32| | |
| | ----| |---- ----| |---- | |
| | | | | | | |
| | ---- | | | | ---- | |
| | |BN13| | | | | |BN33| | |
| -----------+---- ---------------- ----+----------- |
| \ / |
| \ ---------------- / |
| \ | | / |
| \ |---- ----| / |
| ----+BN41| |BN42+---- |
| |---- ----| |
| | | |
| | ----- | |
| | |PCE 4| | |
| | ----- | |
| | | |
| | Domain 4 | |
| ---------------- |
| |
-----------------------------------------------------------------
Hierarchical domain topology from RFC6805
Section 3.3.1 of [I-D.ietf-pce-stateful-hpce]describes the per-domain stitched LSP mode and list all the steps needed. To support SL based stiching, using the reference architecture described in Figure above, the steps are modified as follows (note that we do not use PKS in this example for simplicity):
Step 1: initialization
The P-PCE (PCE5) is requested to initiate a LSP. Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to determine the end to end path, which are broken into per-domain LSPs e.g. {S-BN41, BN41-BN33, BN33-D}
Step 2: LSP (BN33-D) at PCE3:
Step 3: LSP (BN41-BN33) at PCE4
Step 3: LSP (S-BN41) for PCE1
In this way, per-domain LSP are stitched together using the stitching label (SL). The per-domain LSP MUST be setup from the destination domain towards the source domain one after the other.
Once the per-domain LSP is setup, the entry BN chooses a free label for the Stitching Label SL and add a new entry in its MPLS LFIB with this SL label. The SL from the destination domain is propagated to adjacent transit domain, towards the source domain at each step. This happens through the entry BN to C-PCE to the P-PCE and vice- versa. In case of RSVP-TE, the entry BN further propagates the SL label to the exit BN via RSVP-TE. In case of SR, the SL label is pushed as part of the SR label stack.
This section describe how inter-domain LSPs could be manage.
First, in order to manage inter-domain tunnels composed by the stitching or nesting of local tunnels, it is important to identify them. For this purpose, PLSP-ID managed by PCEs are combined to one provided by PCCs to form global identifier as follow:
Further reference to the inter-domain tunnel will use this PLSP-ID(i). In Backward Recursive method, PCE(i) MUST replace the PLSP-ID(i) by PLSP-ID(i+1) in the PCUpd message before propagating it to PCE(i+1) and PCE(i) MUST replace the PLSP-ID(i+1) by PLSP-ID(i) in the PCRpt message before propagating it to the PCE(i-1). In Hierarchical method, Parent PCE MUST use the corresponding PLSP-ID(i) of the Child PCE(i).
For the Backward Recursive method, each domain manages their respective local LSP tunnel part of an inter-domain path 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. The same behavior apply to PLSP-ID(i). In Hierarchical method, the Parent PCE MUST ensure the correct distribution of Stitching Label SL(i) to Child PCE(i-1. The PLSP-ID(i) is kept for the usage of the Parent PCE and thus is not propagated.
If a PCE(i) needs to modify its local LSP tunnel(i) with PCUpd message to the PCC BN-en(i), once PCRpt message received by the PCC BN-en(i), it MUST sends a new PCRpt message to its neighbor PCE(i-1) in Backward Recursive method, respectively to Parent PCE in Hierarchical method, to advertise it of the modification. In particular. In this case PLSP-ID(i) is used to identify the inter-domain tunnel. PCE(i-1), respectively the Parent PCE, MUST propagate the PCRpt message if the modification imply the previous domain e.g. if the PCRpt indicates that the Stitching Label SL(i) has changed.
PCE(1), respectively Parent PCE, could modify the inter-domain path. For that purpose, it MUST sends a PCUpd message to its neighbor PCEs, respectively Child PCE, using the PLSP-ID it received. Each PCE(i) MUST process PCUpd message the same way they process PCInitiate message as define in section 3.1 for Backward Recursive method and in section 4.1 for Hierarchical method.
In case a failure appear in domain(i), e.g. tunnel becoming down, PCE(i) MUST sends a PCRpt message to its neighbor PCE(i-1), respectively its Parent PCE to advertise it of the problem in its local part of the inter-domain path. Once PCE(1), respectively Parent PCE, receives this PCRpt message indicating that the tunnel is down, it is up to the PCE(1), respectively Parent PCE to take appropriate correction e.g. start a new path computation to update the ERO.
Modification of local LSP tunnel, BN-en(i) and BN-ex(i) is left for further study.
Deletion of inter-domain LSP is only possible by the inter-domain tunnel initiator. For Backward Recursive method, PCInitiate message with R flag set to 1 and PLSP-ID set accordingly to section 5.1, is sent by PCE(1) to PCE(n) through PCE(i) and process the same way as describe in section 3.1. For Hierarchical method, PCInitiate message with R flag set to 1 is sent by the Parent PCE to each Child PCE(i) with corresponding PLSP-ID(i) and process accordingly to section 4.1. Each domain PCE(i) is responsible to delete its part of the tunnel and PCC MUST remove the Stitching label SL in its LFIB in addition to the tunnel when it received the PCInitiate message with the R flag set to 1 and corresponding PLSP-ID.
The newly introduce Stitching Label SL serves to stitch or nest part of local LSP tunnels to form an inter-domain path. 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 paths into a higher hierarchical tunnel to carry all these local LSP tunnels from one BN-en(i) to one BN-ex(i).
To use Segment Routing instead of RSVP-TE to setup the local LSP tunnels as defined in draft pce segment routing, PCE(i) MUST send PCInitiate message with LSP-TYPE = TBD3 instead of TBD2 to advertise their respective PCC that the local LSP tunnels is enforce by means of Segment Routing. Stitching Label SL(i) will be inserted in the label stack in order to become the top label in the stack when the packet reach BN-en(i+1): BN-en(i) MUST install in its MPLS LFIB a SWAP instruction to the replace the incoming Stitching Label SL(i) by the label stack given by the ERO(i) plus the Stitching Label SL(i+1) as the last label in the stack. The Stitching Label SL(i) serves as entry FEC for BN-en(i) to identify the packets that follow the next Segment Path. When packet reach BN-ex(i), the last label in the stack before the label SL(i+1) corresponds to the SID that design BN-en(i+1). This inter-domain SID could be obtain as per draft Egress Peer Engineering.
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 path 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 BN-en(i+1). This Stitching Label could be swap as usual if the next domain uses RSVP-TE tunnel. When the previous domain uses a RSVP-TE tunnel, the Stitching Label will serve as key for the BN-en(i+1) to determine which label stack it must push on top of the packet for a Segment Routing path.
During the instantiation procedure, if PCE(i) decides to reuse a local tunnel which is not yet part of an inter-domain tunnel, it SHOULD send a PCUpd message with LSP-TYPE = TBD2 to the PCC BN-en(i) in order to request a Stitching Label SL(i) and new ERO(i) to include the Stitching Label SL(i+1) and the associated link to the previous ERO.
[I-D.ietf-teas-actn-framework] describes framework for Abstraction and Control of TE Networks (ACTN), where each Physical Network Controller (PNC) is equivalent to C-PCE and P-PCE is the Multi-Domain Service Coordinator (MDSC). The Per domain stitched LSP as per the Hierarchical PCE architecture described in Section 3.3.1 and Section 4.1 of [I-D.ietf-pce-stateful-hpce] is well suited for ACTN. The stitching label (SL) mechanism as described in this document is well suited for ACTN when per domain LSP needs to be stitched to form an E2E tunnel or a VN Member. It is to be noted that certain VNs require isolation from other clients. The stitching label mechanism described in this document can be applicable to the VN isolation use-case by uniquely identifying the concatenated stitching labels across multi-domain only to a certain VN member or an E2E tunnel.
Inter-layer scenario is left for further study.
Draft 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 path is setup using Backward Recursive method | This Document |
| TBD2 | Inter-Domain Traffic engineering local path is setup using RSVP-TE | This Document |
| TBD3 | Inter-Domain Traffic engineering local path is setup using Segment Routing | This Document |
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 |
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 or use any other secure tunnel mechanism e.g. IPsec tunnel to transport PCEP session between PCE.
The authors want to thanks PCE's WG members.
This work has been performed in the framework of the H2020-ICT-2014 project 5GEx (Grant Agreement no. 671636), which is partially funded by the European Commission. This information reflects the consortium's view, but neither the consortium nor the European Commission are liable for any use that may be done of the information contained therein.