Internet DRAFT - draft-chen-pce-compute-backup-egress
draft-chen-pce-compute-backup-egress
Internet Engineering Task Force H. Chen
Internet-Draft Futurewei
Intended status: Standards Track 10 January 2024
Expires: 13 July 2024
Extensions to the Path Computation Element Communication Protocol (PCEP)
for Backup Egress of a Traffic Engineering Label Switched Path
draft-chen-pce-compute-backup-egress-23
Abstract
This document presents extensions to the Path Computation Element
Communication Protocol (PCEP) for a PCC to send a request for
computing a backup egress for an MPLS TE P2MP LSP or an MPLS TE P2P
LSP to a PCE and for a PCE to compute the backup egress and reply to
the PCC with a computation result for the backup egress.
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 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 13 July 2024.
Copyright Notice
Copyright (c) 2024 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Chen Expires 13 July 2024 [Page 1]
Internet-Draft Find Backup Egress January 2024
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Conventions Used in This Document . . . . . . . . . . . . . . 3
4. Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . 3
4.1. Backup Egress Capability Advertisement . . . . . . . . . 3
4.1.1. Capability TLV in Existing PCE Discovery Protocol . . 3
4.1.2. Open Message Extension . . . . . . . . . . . . . . . 5
4.2. Request and Reply Message Extension . . . . . . . . . . . 5
4.2.1. RP Object Extension . . . . . . . . . . . . . . . . . 5
4.2.2. External Destination Nodes . . . . . . . . . . . . . 6
4.2.3. Constraints between Egress and Backup Egress . . . . 11
4.2.4. Constraints for Backup Path . . . . . . . . . . . . . 11
4.2.5. Backup Egress Node . . . . . . . . . . . . . . . . . 11
4.2.6. Backup Egress PCEP Error Objects and Types . . . . . 12
4.2.7. Request Message Format . . . . . . . . . . . . . . . 12
4.2.8. Reply Message Format . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6.1. Backup Egress Capability Flag . . . . . . . . . . . . . . 13
6.2. Backup Egress Capability TLV . . . . . . . . . . . . . . 14
6.3. Request Parameter Bit Flags . . . . . . . . . . . . . . . 14
6.4. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
RFC 4655 "A Path Computation Element-(PCE) Based Architecture"
describes a set of building blocks for constructing solutions to
compute Point-to-Point (P2P) Traffic Engineering (TE) label switched
paths across multiple areas or Autonomous System (AS) domains. A
typical PCE-based system comprises one or more path computation
servers, traffic engineering databases (TED), and a number of path
computation clients (PCC). A routing protocol is used to exchange
traffic engineering information from which the TED is constructed. A
PCC sends a Point-to-Point traffic engineering Label Switched Path
(LSP) computation request to the path computation server, which uses
the TED to compute the path and responses to the PCC with the
computed path. A path computation server is named as a PCE. The
communications between a PCE and a PCC for Point-to-Point label
switched path computations follow the PCE communication protocol
(PCEP).
Chen Expires 13 July 2024 [Page 2]
Internet-Draft Find Backup Egress January 2024
RFC6006 "Extensions to PCEP for Point-to-Multipoint Traffic
Engineering Label Switched Paths" describes extensions to PCEP to
handle requests and responses for the computation of paths for P2MP
TE LSPs.
This document defines extensions to the Path Computation Element
Communication Protocol (PCEP) for a PCC to send a request for
computing a backup egress node for an MPLS TE P2MP LSP or an MPLS TE
P2P LSP to a PCE and for a PCE to compute the backup egress node and
reply to the PCC with a computation result for the backup egress
node.
2. Terminology
This document uses terminologies defined in RFC5440, and RFC4875.
3. Conventions Used in This Document
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.
4. Extensions to PCEP
This section describes the extensions to PCEP for computing a backup
egress of an MPLS TE P2MP LSP and an MPLS TE P2P LSP.
4.1. Backup Egress Capability Advertisement
4.1.1. Capability TLV in Existing PCE Discovery Protocol
An option for advertising a PCE capability for computing a backup
egress for an MPLS TE P2MP LSP or an MPLS TE P2P LSP is to define two
new flags. One new flag in the OSPF and IS-IS PCE Capability Flags
indicates the capability that a PCE is capable to compute a backup
egress for an MPLS TE P2MP LSP; and another new flag in the OSPF and
IS-IS PCE Capability Flags indicates the capability that a PCE is
capable to compute a backup egress for an MPLS TE P2P LSP.
The format of the PCE-CAP-FLAGS sub-TLV is as follows:
Chen Expires 13 July 2024 [Page 3]
Internet-Draft Find Backup Egress January 2024
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 = 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PCE Capability Flags ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 5
Length: Multiple of 4 octets
Value: This contains an array of units of 32-bit flags
numbered from the most significant as bit zero, where
each bit represents one PCE capability.
The following capability bits have been assigned by IANA:
Bit Capabilities
0 Path computation with GMPLS link constraints
1 Bidirectional path computation
2 Diverse path computation
3 Load-balanced path computation
4 Synchronized path computation
5 Support for multiple objective functions
6 Support for additive path constraints
(max hop count, etc.)
7 Support for request prioritization
8 Support for multiple requests per message
9 Global Concurrent Optimization (GCO)
10 P2MP path computation
11-31 Reserved for future assignments by IANA.
Reserved bits SHOULD be set to zero on transmission and MUST be
ignored on receipt.
For the backup egress capabilities, one bit such as bit 13 may be
assigned to indicate that a PCE is capable to compute a backup egress
for an MPLS TE P2MP LSP and another bit such as bit 14 may be
assigned to indicate that a PCE is capable to compute a backup egress
for an MPLS TE P2P LSP as follows.
Bit Capabilities
13 Backup egress computation for P2MP LSP
14 Backup egress computation for P2P LSP
15-31 Reserved for future assignments by IANA.
Chen Expires 13 July 2024 [Page 4]
Internet-Draft Find Backup Egress January 2024
4.1.2. Open Message Extension
If a PCE does not advertise its backup egress compution capability
during discovery, PCEP should be used to allow a PCC to discover,
during the Open Message Exchange, which PCEs are capable of
supporting backup egress computation.
To achieve this, we extend the PCEP OPEN object by defining a new
optional TLV to indicate the PCE's capability to perform backup
egress computation for an MPLS TE P2MP LSP and an MPLS TE P2P LSP.
We request IANA to allocate a value such as 8 from the "PCEP TLV Type
Indicators" subregistry, as documented in Section below ("Backup
Egress Capability TLV"). The description is "backup egress capable",
and the length value is 2 bytes. The value field is set to indicate
the capability of a PCE for backup egress computation for an MPLS TE
LSP in details.
We can use flag bits in the value field in the same way as the PCE
Capability Flags described in the previous section.
The inclusion of this TLV in an OPEN object indicates that the sender
can perform backup egress computation for an MPLS TE P2MP LSP or an
MPLS TE P2P LSP.
The capability TLV is meaningful only for a PCE, so it will typically
appear only in one of the two Open messages during PCE session
establishment. However, in case of PCE cooperation (e.g., inter-
domain), when a PCE behaving as a PCC initiates a PCE session it
SHOULD also indicate its path computation capabilities.
4.2. Request and Reply Message Extension
This section describes extensions to the existing RP (Request
Parameters) object to allow a PCC to request a PCE for computing a
backup egress of an MPLS TE P2MP LSP or an MPLS TE P2P LSP when the
PCE receives the PCEP request.
4.2.1. RP Object Extension
The following flags are added into the RP Object:
The T bit is added in the flag bits field of the RP object to tell
the receiver of the message that the request/reply is for computing a
bcakup egress of an MPLS TE P2MP LSP and an MPLS TE P2P LSP.
Chen Expires 13 July 2024 [Page 5]
Internet-Draft Find Backup Egress January 2024
o T ( Backup Egress bit - 1 bit):
0: This indicates that this is not PCReq/PCRep
for backup egress.
1: This indicates that this is PCReq or PCRep message
for backup egress.
The IANA request is referenced in Section below (Request Parameter
Bit Flags) of this document.
This T bit with the N bit defined in RFC 6006 can indicate whether a
request/reply is for a bcakup egress of an MPLS TE P2MP LSP or an
MPLS TE P2P LSP.
o T = 1 and N = 1: This indicates that this is a PCReq/PCRep
message for backup egress of an MPLS TE
P2MP LSP.
o T = 1 and N = 0: This indicates that this is a PCReq/PCRep
message for backup egress of an MPLS TE
P2P LSP.
4.2.2. External Destination Nodes
In addition to the information about the path that an MPLS TE P2MP
LSP or an MPLS TE P2P LSP traverses, a request message may comprise
other information that may be used for computing the backup egress
for the P2MP LSP or P2P LSP. For example, the information about an
external destination node, to which data traffic is delivered from an
egress node of the P2MP LSP or P2P LSP, is useful for computing a
backup egress node.
4.2.2.1. External Destination Nodes Object
The PCC can specify an external destination nodes (EDN) Object. In
order to represent the external destination nodes efficiently, we
define two types of encodes for the external destination nodes in the
object.
One encode indicates that the EDN object contains an external
destination node for every egress node of an MPLS TE P2MP LSP or an
MPLS TE P2P LSP. The order of the external destination nodes in the
object is the same as the egress node(s) of the P2MP LSP or P2P LSP
contained in the PCE messages.
Chen Expires 13 July 2024 [Page 6]
Internet-Draft Find Backup Egress January 2024
Another encode indicates that the EDN object contains a list of
egress node and external destination node pairs. For an egress node
and external destination node pair, the data traffic is delivered to
the external destination node from the egress node of the LSP.
The format of the external destination nodes (EDN) object boby for
IPv4 with the first type of encodes is illustrated as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encode of External Destination Nodes (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the external destination nodes (EDN) object boby for
IPv4 with the second type of encodes is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encode of External Destination Nodes (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chen Expires 13 July 2024 [Page 7]
Internet-Draft Find Backup Egress January 2024
The format of the external destination nodes (EDN) object boby for
IPv6 with the first type of encodes is illustrated as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encode of External Destination Nodes (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the external destination nodes (EDN) object boby for
IPv6 with the second type of encodes is illustrated below:
Chen Expires 13 July 2024 [Page 8]
Internet-Draft Find Backup Egress January 2024
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encode of External Destination Nodes (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Egress IPv6 address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Egress IPv6 address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Egress IPv6 address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| External Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The object can only be carried in a PCReq message. A Path Request
may carry at most one external destination nodes Object.
The Object-Class and Object-types will need to be allocated by IANA.
The IANA request is documented in Section below (PCEP Objects).
4.2.2.2. New Type of END-POINTS Objects
Alternatively, we may use END-POINTS to represent external
destination nodes in a request message for computing backup egress
nodes of MPLS LSP.
The format of the external destination nodes (EDN) END-POINTS object
boby for IPv4 with the first type of encodes is illustrated as
follows:
Chen Expires 13 July 2024 [Page 9]
Internet-Draft Find Backup Egress January 2024
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Compact External Destination Nodes Type (12) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The new type of END-POINTS is Compact External Destination Nodes Type
(12). The final value for the type will be assigned by IANA. The
EDN END-POINTS object of type 12 contains an external destination
node for every egress node of an MPLS TE P2MP LSP or an MPLS TE P2P
LSP. The order of the external destination nodes in the object is
the same as the egress node(s) of the P2MP LSP or P2P LSP contained
in the PCE messages.
The format of the external destination nodes END-POINTS object boby
for IPv4 with the second type of encodes is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination Nodes Type (13) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chen Expires 13 July 2024 [Page 10]
Internet-Draft Find Backup Egress January 2024
The new type of END-POINTS is External Destination Nodes Type (13).
The final value for the type will be assigned by IANA. The EDN END-
POINTS object of type 13 contains a list of egress node and external
destination node pairs. For an egress node and external destination
node pair, the data traffic is delivered to the external destination
node from the egress node of the LSP.
4.2.3. Constraints between Egress and Backup Egress
A request message sent to a PCE from a PCC for computing a backup
egress of an MPLS TE P2MP LSP or an MPLS TE P2P LSP may comprise a
constraint indicating that there must be a path from the backup
egress node to be computed to the egress node of the P2MP LSP or P2P
LSP and that the length of the path is within a given hop limit such
as one hop.
This constraint can be considered as default by a PCE or explicitly
sent to the PCE by a PCC [TBD].
4.2.4. Constraints for Backup Path
A request message sent to a PCE from a PCC for computing a backup
egress of a P2MP LSP or P2P LSP may comprise a constraint indicating
that the backup egress node to be computed may not be a node on the
P2MP LSP or P2P LSP. In addition, the request message may comprise a
list of nodes, each of which is a candidate for the backup egress
node.
A request message sent to a PCE from a PCC for computing a backup
egress of a P2MP LSP or P2P LSP may comprise a constraint indicating
that there must be a path from the previous hop node of the egress
node of the P2MP LSP or P2P LSP to the backup egress node to be
computed and that there is not an internal node of the path from the
previous hop node of the egress node of the P2MP LSP or P2P LSP to
the backup egress that is on the path of the P2MP LSP or P2P LSP.
Most of these constraints for the backup path can be considered as
default by a PCE. The constraints for the backup path may be
explicitly sent to the PCE by a PCC [TBD].
4.2.5. Backup Egress Node
The PCE may send a reply message to the PCC in return to the request
message for computing a new backup egress node or a number of backup
egress nodes. The reply message may comprise information about the
computed backup egress node(s), which is contained in the path(s)
from the previous-hop node of the egress node of the P2MP LSP or P2P
LSP to the backup egress node(s) computed.
Chen Expires 13 July 2024 [Page 11]
Internet-Draft Find Backup Egress January 2024
4.2.6. Backup Egress PCEP Error Objects and Types
In some cases, the PCE may not complete the backup egress computation
as requested, for example based on a set of constraints. As such,
the PCE may send a reply message to the PCC that indicates an
unsuccessful backup egress computation attempt. The reply message
may comprise a PCEP-error object, which may comprise an error-value,
error-type and some detail information.
4.2.7. Request Message Format
The PCReq message is encoded as follows using RBNF as defined in
[RFC5511].
Below is the message format for a request message:
<PCReq Message>::= <Common Header>
[<svec-list>]
<request>
<request>::= <RP> <end-point-rro-pair-list>
[<OF>] [<LSPA>] [<BANDWIDTH>]
[<metric-list>]
[<EDNO>]
[<IRO>]
[<LOAD-BALANCING>]
where:
<EDNO> is an external destination nodes object.
The definitions for svec-list, RP, end-point-rro-pair-list, OF, LSPA,
BANDWIDTH, metric-list, IRO, and LOAD-BALANCING are described in
RFC5440 and RFC6006.
4.2.8. Reply Message Format
The PCRep message is encoded as follows using RBNF as defined in
[RFC5511].
Below is the message format for a reply message:
Chen Expires 13 July 2024 [Page 12]
Internet-Draft Find Backup Egress January 2024
<PCRep Message>::= <Common Header>
<response>
<response>::= <RP>
<end-point-path-pair-list>
[<NO-PATH>]
[<attribute-list>]
where:
<end-point-path-pair-list>::=
[<END-POINTS>]<path>[<end-point-path-pair-list>]
<path> ::= (<ERO>|<SERO>) [<path>]
<attribute-list>::= [<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
The definitions for RP, NO-PATH, END-POINTS, OF, LSPA, BANDWIDTH,
metric-list, IRO, and SERO are described in RFC5440, RFC6006 and
RFC4875.
5. Security Considerations
The mechanism described in this document does not raise any new
security issues for the PCEP, OSPF or IS-IS protocols.
6. IANA Considerations
This section specifies requests for IANA allocation.
6.1. Backup Egress Capability Flag
Two new OSPF Capability Flags are defined in this document to
indicate the capabilities for computing a backup egress for an MPLS
TE P2MP LSP and an MPLS TE P2P LSP. IANA is requested to make the
assignment from the "OSPF Parameters Path Computation Element (PCE)
Capability Flags" registry:
Bit Description Reference
13 Backup egress for P2MP LSP This I-D
14 Backup egress for P2P LSP This I-D
Chen Expires 13 July 2024 [Page 13]
Internet-Draft Find Backup Egress January 2024
6.2. Backup Egress Capability TLV
A new backup egress capability TLV is defined in this document to
allow a PCE to advertize its backup egress computation capability.
IANA is requested to make the following allocation from the "PCEP TLV
Type Indicators" sub-registry.
Value Description Reference
8 Backup egress capable This I-D
6.3. Request Parameter Bit Flags
A new RP Object Flag has been defined in this document. IANA is
requested to make the following allocation from the "PCEP RP Object
Flag Field" Sub-Registry:
Bit Description Reference
15 Backup egress (T-bit) This I-D
6.4. PCEP Objects
An External Destination Nodes Object-Type is defined in this
document. IANA is requested to make the following Object-Type
allocation from the "PCEP Objects" sub-registry:
Object-Class Value 34
Name External Destination Nodes
Object-Type 1: IPv4
2: IPv6
3-15: Unassigned
Reference This I-D
7. Acknowledgement
The author would like to thank Ramon Casellas, Dhruv Dhody and
Quintin Zhao for their valuable comments on this draft.
8. References
8.1. Normative References
Chen Expires 13 July 2024 [Page 14]
Internet-Draft Find Backup Egress January 2024
[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>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[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>.
[RFC4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
DOI 10.17487/RFC4875, May 2007,
<https://www.rfc-editor.org/info/rfc4875>.
[RFC6006] Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
Ali, Z., and J. Meuric, "Extensions to the Path
Computation Element Communication Protocol (PCEP) for
Point-to-Multipoint Traffic Engineering Label Switched
Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
<https://www.rfc-editor.org/info/rfc6006>.
8.2. Informative References
[RFC4655] Farrel, A., Vasseur, J.-P., 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>.
[RFC5862] Yasukawa, S. and A. Farrel, "Path Computation Clients
(PCC) - Path Computation Element (PCE) Requirements for
Point-to-Multipoint MPLS-TE", RFC 5862,
DOI 10.17487/RFC5862, June 2010,
<https://www.rfc-editor.org/info/rfc5862>.
Chen Expires 13 July 2024 [Page 15]
Internet-Draft Find Backup Egress January 2024
Author's Address
Huaimo Chen
Futurewei
Boston, MA
United States of America
Email: Huaimo.chen@futurewei.com
Chen Expires 13 July 2024 [Page 16]
