Internet DRAFT - draft-ietf-pce-multipath
draft-ietf-pce-multipath
PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: 19 July 2024 Ciena Corporation
T. Saad
V. Beeram
Juniper Networks, Inc.
H. Bidgoli
Nokia
B. Yadav
Ciena
S. Peng
Huawei Technologies
G. Mishra
Verizon Inc.
16 January 2024
PCEP Extensions for Signaling Multipath Information
draft-ietf-pce-multipath-10
Abstract
Certain traffic engineering path computation problems require
solutions that consist of multiple traffic paths, that together form
a solution. Returning just one single traffic path does not provide
a valid solution. This document defines a mechanism to encode
multiple paths for a single set of objectives and constraints. This
is a generic PCEP mechanism, not specific to any path setup type or
dataplane. The mechanism is applicable to both stateless and
stateful PCEP.
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 19 July 2024.
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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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms and Abbreviations . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Signaling Multiple Segment-Lists of an SR
Candidate-Path . . . . . . . . . . . . . . . . . . . . . 4
3.2. Splitting of Requested Bandwidth . . . . . . . . . . . . 4
3.3. Reverse Path Information . . . . . . . . . . . . . . . . 4
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 5
4.1. Path Attributes Object . . . . . . . . . . . . . . . . . 5
4.2. Multipath Weight TLV . . . . . . . . . . . . . . . . . . 5
4.3. Multipath Backup TLV . . . . . . . . . . . . . . . . . . 6
4.4. Multipath Opposite Direction Path TLV . . . . . . . . . . 7
4.5. Composite Candidate Path . . . . . . . . . . . . . . . . 8
4.5.1. Per-Flow Candidate Path . . . . . . . . . . . . . . . 9
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Capability Negotiation . . . . . . . . . . . . . . . . . 9
5.1.1. Multipath Capability TLV . . . . . . . . . . . . . . 10
5.2. Path ID . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3. Signaling Multiple Paths for Loadbalancing . . . . . . . 11
5.4. Signaling Multiple Paths for Protection . . . . . . . . . 12
6. PCEP Message Extensions . . . . . . . . . . . . . . . . . . . 12
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. SR Policy Candidate-Path with Multiple Segment-Lists . . 13
7.2. Two Primary Paths Protected by One Backup Path . . . . . 14
7.3. Composite Candidate Path . . . . . . . . . . . . . . . . 15
7.4. Opposite Direction Tunnels . . . . . . . . . . . . . . . 15
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
8.1. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 18
8.2. Ciena Corp . . . . . . . . . . . . . . . . . . . . . . . 18
8.3. Huawei Technologies . . . . . . . . . . . . . . . . . . . 18
8.4. Juniper Networks . . . . . . . . . . . . . . . . . . . . 19
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9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. PCEP Object . . . . . . . . . . . . . . . . . . . . . . . 19
9.2. PCEP TLV . . . . . . . . . . . . . . . . . . . . . . . . 19
9.3. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 20
9.4. Flags in the Multipath Capability TLV . . . . . . . . . . 20
9.5. Flags in the Path Attribute Object . . . . . . . . . . . 20
9.6. Flags in the Multipath Backup TLV . . . . . . . . . . . . 21
9.7. Flags in the Multipath Opposite Direction Path TLV . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 21
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
13.1. Normative References . . . . . . . . . . . . . . . . . . 22
13.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Segment Routing Policy for Traffic Engineering [RFC9256] details the
concepts of SR Policy and approaches to steering traffic into an SR
Policy. In particular, it describes the SR candidate-path as a
collection of one or more Segment-Lists. The current PCEP standards
only allow for signaling of one Segment-List per Candidate-Path.
PCEP extension to support Segment Routing Policy Candidate Paths
[I-D.ietf-pce-segment-routing-policy-cp] specifically avoids defining
how to signal multiple Segment-Lists.
This document defines the required extensions that allow the
signaling of multipath information via PCEP. Although these
extensions are motivated by the SR Policy use case, they are also
applicable to other data plane types.
2. Terminology
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”,
“SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and
“OPTIONAL” in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Terms and Abbreviations
The following terms are used in this document:
ECMP:
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Equal Cost Multi Path, equally distributing traffic among multiple
paths/links, where each path/link gets the same share of traffic
as others.
W-ECMP:
Weighted ECMP, un-equally distributing traffic among multiple
paths/links, where some paths/links get more traffic than others.
3. Motivation
This extension is motivated by the use-cases described below.
3.1. Signaling Multiple Segment-Lists of an SR Candidate-Path
The Candidate-Path of an SR Policy is the unit of signaling in PCEP,
see [I-D.ietf-pce-segment-routing-policy-cp]. Each Candidate-Path
can contain multiple Segment-Lists and each Segment-List is encoded
by one ERO. However, each PCEP LSP can contain only a single ERO,
which prevents us from encoding multiple Segment-Lists within the
same SR Candidate-Path.
3.2. Splitting of Requested Bandwidth
A PCC may request a path with 80 Gbps of bandwidth, but all links in
the network have only 60 Gbps capacity. The PCE can return two
paths, that can together carry 80 Gbps. The PCC can then equally or
unequally split the incoming 80 Gbps of traffic among the two paths.
Section 4.2 introduces a new TLV that carries the path weight that
facilitates control of load-balancing of traffic among the multiple
paths.
3.3. Reverse Path Information
Path Computation Element Communication Protocol (PCEP) Extensions for
Associated Bidirectional Label Switched Paths (LSPs) [RFC9059]
defines a mechanism in PCEP to associate two opposite direction SR
Policy Candidate Paths. However, within each Candidate Path there
can be multiple Segment-Lists, and [RFC9059] does not define a
mechanism to specify Segment-List to Segment-List mapping between the
forward and reverse Candidate Paths. Certain applications such as
Circuit Style SR Policy [I-D.schmutzer-pce-cs-sr-policy], require the
knowledge of reverse path(s) per Segment-List, not just per Candidate
path. For example, when the headend knows the reverse Segment-List
for each forward Segment-List, then PM/BFD can run a separate session
on every Segment-List, by imposing a double stack (forward stack
followed by reverse stack) on the packet. If the reverse Segment-
List is co-routed with the forward Segment-List, then the PM/BFD
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session would traverse the same links in the forward and reverse
directions, thus allowing to detect link/node failures in both
directions.
4. Protocol Extensions
4.1. Path Attributes Object
We define the PATH-ATTRIB object that is used to carry per-path
information and to act as a separator between several ERO/RRO objects
in the <intended-path>/<actual-path> RBNF element. The PATH-ATTRIB
object always precedes the ERO/RRO that it applies to. If multiple
ERO/RRO objects are present, then each ERO/RRO object MUST be
preceded by an PATH-ATTRIB object that describes it.
The PATH-ATTRIB Object-Class value is (45).
The PATH-ATTRIB Object-Type value is 1.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |R| O |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PATH-ATTRIB object format
O (Operational - 3 bits): operational state of the path, same values
as the identically named field in the LSP object [RFC8231].
R (Reverse): Indicates this path is reverse, i.e., it originates on
the LSP destination and terminates on the LSP source (usually the PCC
headend itself). Paths with this flag set serve only informational
purpose to the PCC.
Path ID: 4-octet identifier that identifies a path (encoded in the
ERO/RRO) within the set of multiple paths under the PCEP LSP. See
Section 5.2 for details.
4.2. Multipath Weight TLV
New MULTIPATH-WEIGHT TLV is optional in the PATH-ATTRIB object.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MULTIPATH-WEIGHT TLV format
Type: (61) for “MULTIPATH-WEIGHT” TLV.
Length: 4.
Weight: weight of this path within the multipath, if W-ECMP is
desired. The fraction of flows a specific ERO/RRO carries is derived
from the ratio of its weight to the sum of all other multipath ERO/
RRO weights.
When the MULTIPATH-WEIGHT TLV is absent from the PATH-ATTRIB object,
or the PATH-ATTRIB object is absent from the <intended-path>/<actual-
path>, then the Weight of the corresponding path is taken to be “1”.
4.3. Multipath Backup TLV
New MULTIPATH-BACKUP TLV is optional in the PATH-ATTRIB object.
This TLV is used to specify protecting path(s), similar to FRR or TI-
LFA. This functionality is not part of the SR Policy Architecture
[RFC9256], but is something optional that MAY be implemented for
certain specialized use cases.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path Count | Flags |B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 3: MULTIPATH-BACKUP TLV format
Type: (62) for “MULTIPATH-BACKUP” TLV
Length: 4 + (N * 4) (where N is the Backup Path Count)
Backup Path Count: Number of backup path(s).
B: If set, indicates a pure backup path. This is a path that only
carries rerouted traffic after the protected path fails. If this
flag is not set, or if the MULTIPATH-BACKUP TLV is absent, then the
path is assumed to be primary that carries normal traffic.
Backup Path ID(s): a series of 4-octet identifier(s) that identify
the backup path(s) in the set that protect this primary path.
4.4. Multipath Opposite Direction Path TLV
New MULTIPATH-OPPDIR-PATH TLV is optional in the PATH-ATTRIB object.
Multiple instances of the TLV are allowed in the same PATH-ATTRIB
object. This TLV encodes a many-to-many mapping between forward and
reverse paths.
Many-to-many mapping means that a single forward path MAY map to
multiple reverse paths and conversely that a single reverse path MAY
map to multiple forward paths. Many-to-many mapping can happen for
an SR Policy, when a Segment-List contains Node Segment(s) which
traverse parallel links at the midpoint. The reverse of this
Segment-List may not be able to be expressed as a single Reverse
Segment-List, but need to return multiple Reverse Segment-Lists to
cover all the parallel links at the midpoint.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (MBZ) | Flags |L|N|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opposite Direction Path ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: MULTIPATH-OPPDIR-PATH TLV format
Type: (63) for “MULTIPATH-OPPDIR-PATH” TLV
Length: 16.
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N (Node co-routed): If set, indicates this path is node co-routed
with its opposite direction path, specified in this TLV. Two
opposite direction paths are node co-routed if they traverse the same
nodes, but MAY traverse different links.
L (Link co-routed): If set, indicates this path is link co-routed
with its opposite directions path, specified in this TLV. Two
opposite direction paths are link co-routed if they traverse the same
links (but in the opposite directions).
Opposite Direction Path ID: Identifies a path that goes in the
opposite direction to this path. If no such path exists, then this
field MUST be set to 0x0, which is reserved to indicate the absense
of a Path ID.
Multiple instances of this TLV present in the same PATH-ATTRIB object
indicate that there are multiple opposite-direction paths
corresponding to the given path. This allows for many-to-many
relationship among the paths of two opposite direction LSPs.
Whenever path A references another path B as being the opposite-
direction path, then path B SHOULD also reference path A as its own
opposite-direction path. Furthermore, their values of the R-flag
(Reverse) in the PATH-ATTRIB object MUST have opposite values.
PCC MAY skip sending the reverse path information in PCRpt messages,
in cases when the PCE was the original source of the reverse path
information.
See Section 7.4 for an example of usage.
4.5. Composite Candidate Path
SR Policy Architecture [RFC9256] defines the concept of a Composite
Candidate Path. A regular SR Policy Candidate Path outputs traffic
to a set of Segment-Lists, while an SR Policy Composite Candidate
Path outputs traffic recursively to a set of SR Policies on the same
headend. In PCEP, the Composite Candidate Path still consists of
PATH-ATTRIB objects, but ERO is replaced by Color of the recursively
used SR Policy.
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To signal the Composite Candidate Path, we make use of the COLOR TLV,
defined in [I-D.draft-ietf-pce-pcep-color]. For a Composite
Candidate Path, the COLOR TLV is included in the PATH-ATTRIB Object,
thus allowing each Composite Candidate Path to do ECMP/W-ECMP among
SR Policies identified by its constituent Colors. Only one COLOR TLV
SHOULD be included into the PATH-ATTRIB object. If multiple COLOR
TLVs are contained in the PATH-ATTRIB object, only the first one MUST
be processed and the others SHOULD be ignored.
An ERO object MUST be included as per the existing RBNF, this ERO
SHOULD contain no sub-objects. If the head-end receives a non-empty
ERO, the contents SHOULD be ignored.
See Section 7.3 for an example of the encoding.
4.5.1. Per-Flow Candidate Path
Per-Flow Candidate Path builds on top of the concept of the Composite
Candidate Path. Each Path in a Per-Flow Candidate Path is assigned a
3-bit forward class value, which allows QoS classified traffic to be
steered depending on the forward class.
New MULTIPATH-FORWARD-CLASS TLV is optional in the PATH-ATTRIB
object.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | FC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: MULTIPATH-FORWARD-CLASS TLV format
Type: (TBD1) for “MULTIPATH-FORWARD-CLASS” TLV.
Length: 4.
FC: Forward class value that is given by the QoS classifier to
traffic entering the given Candidate Path. Different classes of
traffic that enter the given Candidate Path can be differentially
steered into different Colors.
5. Operation
5.1. Capability Negotiation
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5.1.1. Multipath Capability TLV
New MULTIPATH-CAP TLV is defined. This TLV MAY be present in the
OPEN object during PCEP session establishment.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Multipaths | Flags |C|F|O|B|W|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: MULTIPATH-CAP TLV format
Type: (60) for “MULTIPATH-CAP” TLV.
Length: 4.
Number of Multipaths: From PCC, it tells how many multipaths the PCC
can install in forwarding. From PCE, it tells how many multipaths
the PCE can compute. The value 255 indicates unlimited number. The
value 0 is reserved.
W-flag: whether MULTIPATH-WEIGHT TLV is supported.
B-flag: whether MULTIPATH-BACKUP TLV is supported.
O-flag: whether MULTIPATH-OPPDIR-PATH TLV is supported and requested.
If this flag is set, the PCE SHOULD tell the PCC the reverse path
information, if it is able to.
F-flag: whether MULTIPATH-FORWARD-CLASS TLV is supported.
C-flag: whether Composite Candidate Path (Section 4.5) is supported.
Note that F-flag and C-flag can be set independently, i.e., F-flag
can be set, but C-flag not set, etc.
When PCE computes the LSP path, it MUST NOT return more forward
multipaths than the corresponding value of “Number of Multipaths”
from the MULTIPATH-CAP TLV. If this TLV is absent (from both OPEN
and LSP objects), then the “Number of Multipaths” is assumed to be 1.
From the PCC, the MULTIPATH-CAP TLV MAY also be present in the LSP
object for each individual LSP, to specify per-LSP values. The PCC
MUST NOT include this TLV in the LSP object if the TLV was not
present in the OPEN objects of both PCEP peers. TLV values in the
LSP object override the session default values in the OPEN object.
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For example, the PCC includes this TLV in the OPEN object at session
establishment, setting “Number of Multipaths” to 4 and “O-flag” to 0.
The PCC also includes this TLV in the LSP object for a particular
LSP, setting “Number of Multipaths” to 16 and “O-flag” to 1. This
indicates that the PCC only wants to receive the reverse path
information for that particular LSP and that this LSP can have up to
16 multipaths, while other LSPs can only have up to 4 multipaths.
5.2. Path ID
The Path ID uniquely identifies a Path within the context of an LSP.
Note that when the LSP is an SR Policy Candidate Path, the Paths
within that LSP are the Segment-Lists.
Value 0x0 indicates unallocated Path ID. The value of 0x0 MAY be
used when this Path is not being referenced and the allocation of a
Path ID is not necessary.
Path IDs are allocated by the PCEP peer that owns the LSP. If the
LSP is delegated to the PCE, then the PCE allocates the Path IDs and
sends them in the PCReply/PCUpd/PCInit messages. If the LSP is
locally computed on the PCC, then the PCC allocates the Path IDs and
sends them in the PCReq/PCRpt messages.
If a PCEP speaker detects that there are two Paths with the same Path
ID, then the PCEP speaker SHOULD send PCError message with Error-Type
= 1 (“Reception of an invalid object”) and Error-Value = 38
(“Conflicting Path ID”).
5.3. Signaling Multiple Paths for Loadbalancing
The PATH-ATTRIB object can be used to signal multiple path(s) and
indicate (un)equal loadbalancing amongst the set of multipaths. In
this case, the PATH-ATTRIB is populated for each ERO as follows:
1. The PCE assigns a unique Path ID to each ERO path and populates
it inside the PATH-ATTRIB object. The Path ID is unique within
the context of a PLSP.
2. The MULTIPATH-WEIGHT TLV MAY be carried inside the PATH-ATTRIB
object. A weight is populated to reflect the relative loadshare
that is to be carried by the path. If the MULTIPATH-WEIGHT is
not carried inside a PATH-ATTRIB object, the default weight 1
MUST be assumed when computing the loadshare.
3. The fraction of flows carried by a specific primary path is
derived from the ratio of its weight to the sum of all other
multipath weights.
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5.4. Signaling Multiple Paths for Protection
The PATH-ATTRIB object can be used to describe a set of backup
path(s) protecting a primary path within a PCEP LSP. In this case,
the PATH-ATTRIB is populated for each ERO as follows:
1. The PCE assigns a unique Path ID to each ERO path and populates
it inside the PATH-ATTRIB object. The Path ID is unique within
the context of a PLSP.
2. The MULTIPATH-BACKUP TLV MAY be added inside the PATH-ATTRIB
object for each ERO that is protected. The backup path ID(s) are
populated in the MULTIPATH-BACKUP TLV to reflect the set of
backup path(s) protecting the primary path. The Length field and
Backup Path Number in the MULTIPATH-BACKUP are updated according
to the number of backup path ID(s) included.
3. The MULTIPATH-BACKUP TLV MAY be added inside the PATH-ATTRIB
object for each ERO that is unprotected. In this case,
MULTIPATH-BACKUP does not carry any backup path IDs in the TLV.
If the path acts as a pure backup i.e. the path only carries
rerouted traffic after the protected path(s) fail then the B flag
MUST be set.
Note that primary paths which do not include the MULTIPATH-BACKUP TLV
are assumed to be protected by all the backup paths. I.e., omitting
the TLV is equivalent to including the TLV with all the backup path
IDs filled in.
Note that a given PCC may not support certain backup combinations,
such as a backup path that is itself protected by another backup
path, etc. If a PCC is not able to implement a requested backup
scenario, the PCC SHOULD send a PCError message with Error-Type = 19
(“Invalid Operation”) and Error-Value = 20 (“Not supported path
backup”).
6. PCEP Message Extensions
The RBNF of PCReq, PCRep, PCRpt, PCUpd and PCInit messages currently
use a combination of <intended-path> and/or <actual-path>. As
specified in Section 6.1 of [RFC8231], <intended-path> is represented
by the ERO object and <actual-path> is represented by the RRO object:
<intended-path> ::= <ERO>
<actual-path> ::= <RRO>
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In this standard, we extend these two elements to allow multiple ERO/
RRO objects to be present in the <intended-path>/<actual-path>:
<intended-path> ::= (<ERO>|
(<PATH-ATTRIB><ERO>)
[<intended-path>])
<actual-path> ::= (<RRO>|
(<PATH-ATTRIB><RRO>)
[<actual-path>])
7. Examples
7.1. SR Policy Candidate-Path with Multiple Segment-Lists
Consider the following sample SR Policy, taken from [RFC9256].
SR policy POL1 <headend, color, endpoint>
Candidate-path CP1 <protocol-origin = 20, originator =
100:1.1.1.1, discriminator = 1>
Preference 200
Weight W1, SID-List1 <SID11...SID1i>
Weight W2, SID-List2 <SID21...SID2j>
Candidate-path CP2 <protocol-origin = 20, originator =
100:2.2.2.2, discriminator = 2>
Preference 100
Weight W3, SID-List3 <SID31...SID3i>
Weight W4, SID-List4 <SID41...SID4j>
As specified in [I-D.ietf-pce-segment-routing-policy-cp], CP1 and CP2
are signaled as separate state-report elements and each has a unique
PLSP-ID, assigned by the PCC. Let us assign PLSP-ID 100 to CP1 and
PLSP-ID 200 to CP2.
The state-report for CP1 can be encoded as:
<state-report> =
<LSP PLSP_ID=100>
<ASSOCIATION>
<END-POINT>
<PATH-ATTRIB Path_ID=1 <WEIGHT-TLV Weight=W1>>
<ERO SID-List1>
<PATH-ATTRIB Path_ID=2 <WEIGHT-TLV Weight=W2>>
<ERO SID-List2>
The state-report for CP2 can be encoded as:
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<state-report> =
<LSP PLSP_ID=200>
<ASSOCIATION>
<END-POINT>
<PATH-ATTRIB Path_ID=1 <WEIGHT-TLV Weight=W3>>
<ERO SID-List3>
<PATH-ATTRIB Path_ID=2 <WEIGHT-TLV Weight=W4>>
<ERO SID-List4>
The above sample state-report elements only specify the minimum
mandatory objects, of course other objects like SRP, LSPA, METRIC,
etc., are allowed to be inserted.
Note that the syntax
<PATH-ATTRIB Path_ID=1 <WEIGHT-TLV Weight=W1>>
, simply means that this is PATH-ATTRIB object with Path ID field set
to “1” and with a MULTIPATH-WEIGHT TLV carrying weight of “W1”.
7.2. Two Primary Paths Protected by One Backup Path
Suppose there are 3 paths: A, B, C. Where A,B are primary and C is
to be used only when A or B fail. Suppose the Path IDs for A, B, C
are respectively 1, 2, 3. This would be encoded in a state-report
as:
<state-report> =
<LSP>
<ASSOCIATION>
<END-POINT>
<PATH-ATTRIB Path_ID=1 <BACKUP-TLV B=0, Backup_Paths=[3]>>
<ERO A>
<PATH-ATTRIB Path_ID=2 <BACKUP-TLV B=0, Backup_Paths=[3]>>
<ERO B>
<PATH-ATTRIB Path_ID=3 <BACKUP-TLV B=1, Backup_Paths=[]>>
<ERO C>
Note that the syntax
<PATH-ATTRIB Path_ID=1 <BACKUP-TLV B=0, Backup_Paths=[3]>>
, simply means that this is PATH-ATTRIB object with Path ID field set
to “1” and with a MULTIPATH-BACKUP TLV that has B-flag cleared and
contains a single backup path with Backup Path ID of 3.
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7.3. Composite Candidate Path
Consider the following Composite Candidate Path, taken from
[RFC9256].
SR policy POL100 <headend = H1, color = 100, endpoint = E1>
Candidate-path CP1 <protocol-origin = 20, originator =
100:1.1.1.1, discriminator = 1>
Preference 200
Weight W1, SR policy <color = 1>
Weight W2, SR policy <color = 2>
This is signaled in PCEP as:
<LSP PLSP_ID=100>
<ASSOCIATION>
<END-POINT>
<PATH-ATTRIB Path_ID=1
<WEIGHT-TLV Weight=W1>
<COLOR-TLV Color=1>>
<ERO (empty)>
<PATH-ATTRIB Path_ID=2
<WEIGHT-TLV Weight=W2>
<COLOR-TLV Color=2>>
<ERO (empty)>
7.4. Opposite Direction Tunnels
Consider the two opposite-direction SR Policies between end-points H1
and E1.
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SR policy POL1 <headend = H1, color, endpoint = E1>
Candidate-path CP1
Preference 200
Bidirectional Association = A1
SID-List = <H1,M1,M2,E1>
SID-List = <H1,M3,M4,E1>
Candidate-path CP2
Preference 100
Bidirectional Association = A2
SID-List = <H1,M5,M6,E1>
SID-List = <H1,M7,M8,E1>
SR policy POL2 <headend = E1, color, endpoint = H1>
Candidate-path CP1
Preference 200
Bidirectional Association = A1
SID-List = <E1,M2,M1,H1>
SID-List = <E1,M4,M3,H1>
Candidate-path CP2
Preference 100
Bidirectional Association = A2
SID-List = <E1,M6,M5,H1>
The state-report for POL1, CP1 can be encoded as:
<state-report> =
<LSP PLSP_ID=100>
<BIDIRECTIONAL ASSOCIATION = A1>
<PATH-ATTRIB PathID=1 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=3>>
<ERO <H1,M1,M2,E1>>
<PATH-ATTRIB PathID=2 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=4>>
<ERO <H1,M3,M4,E1>>
<PATH-ATTRIB PathID=3 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=1>>
<ERO <E1,M2,M1,H1>>
<PATH-ATTRIB PathID=4 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=2>>
<ERO <E1,M4,M3,H1>>
The state-report for POL1, CP2 can be encoded as:
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<state-report> =
<LSP PLSP_ID=200>
<BIDIRECTIONAL ASSOCIATION = A2>
<PATH-ATTRIB PathID=1 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=3>>
<ERO <H1,M5,N6,E1>>
<PATH-ATTRIB PathID=2 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=0>>
<ERO <H1,M7,M8,E1>>
<PATH-ATTRIB PathID=3 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=1>>
<ERO <E1,M6,M5,H1>>
The state-report for POL2, CP1 can be encoded as:
<state-report> =
<LSP PLSP_ID=100>
<BIDIRECTIONAL ASSOCIATION = A1>
<PATH-ATTRIB PathID=1 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=3>>
<ERO <E1,M2,M1,H1>>
<PATH-ATTRIB PathID=2 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=4>>
<ERO <E1,M4,M3,H1>>
<PATH-ATTRIB PathID=3 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=1>>
<ERO <H1,M1,M2,E1>>
<PATH-ATTRIB PathID=4 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=2>>
<ERO <H1,M3,M4,E1>>
The state-report for POL2, CP2 can be encoded as:
<state-report> =
<LSP PLSP_ID=200>
<BIDIRECTIONAL ASSOCIATION = A2>
<PATH-ATTRIB PathID=1 R-flag=0
<OPPDIR-PATH-TLV OppositePathID=3>>
<ERO <E1,M6,M5,H1>>
<PATH-ATTRIB PathID=2 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=0>>
<ERO <H1,M7,M8,E1>>
<PATH-ATTRIB PathID=3 R-flag=1
<OPPDIR-PATH-TLV OppositePathID=1>>
<ERO <H1,M5,N6,E1>>
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8. Implementation Status
Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], “this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit”.
8.1. Cisco Systems
Organization: Cisco Systems
Implementation: IOS-XR PCC and PCE
Description: Circuit-Style SR Policies
Maturity Level: Supported feature
Coverage: Multiple Segment-Lists and reverse paths in SR Policy
Contact: mkoldych@cisco.com
8.2. Ciena Corp
Organization: Ciena Corp
Implementation: Head-end and controller
Maturity Level: Proof of concept
Coverage: Full
Contact: byadav@ciena.com
8.3. Huawei Technologies
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Organization: Huawei Technologies Co.,Ltd.
Implementation: Huawei's Router and Controller
Maturity Level: Proof of concept
Coverage: Partial
Contact: tanren@huawei.com
8.4. Juniper Networks
Organization: Juniper Networks
Implementation: PCC
Description: Everything in -06 except Multipath Backup TLV and Multipath Opposite Direction Path TLV.
Maturity Level: Production
Coverage: Partial
Contact: vbeeram@juniper.net
9. IANA Considerations
9.1. PCEP Object
IANA is requested to make the assignment of a new value for the
existing “PCEP Objects” registry as follows:
+--------------+-------------+-------------------+-----------------+
| Object-Class | Name | Object-Type | Reference |
| Value | | Value | |
+--------------+-------------+-------------------+-----------------+
| 45 | PATH-ATTRIB | 1 | This document |
+--------------+-------------+-------------------+-----------------+
9.2. PCEP TLV
IANA is requested to make the assignment of a new value for the
existing “PCEP TLV Type Indicators” registry as follows:
+------------+-----------------------------------+-----------------+
| TLV Type | TLV Name | Reference |
| Value | | |
+------------+-----------------------------------+-----------------+
| 60 | MULTIPATH-CAP | This document |
+------------+-----------------------------------+-----------------+
| 61 | MULTIPATH-WEIGHT | This document |
+------------+-----------------------------------+-----------------+
| 62 | MULTIPATH-BACKUP | This document |
+------------+-----------------------------------+-----------------+
| 63 | MULTIPATH-OPPDIR-PATH | This document |
+------------+-----------------------------------+-----------------+
| TBD1 | MULTIPATH-FORWARD-CLASS | This document |
+------------+-----------------------------------+-----------------+
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9.3. PCEP-Error Object
IANA is requested to make the assignment of a new value for the
existing “PCEP-ERROR Object Error Types and Values” sub-registry of
the PCEP Numbers registry for the following errors:
+------------+-----------------------------------+-----------------+
| Error-Type | Error-Value | Reference |
+------------+-----------------------------------+-----------------+
| 10 | 38 - Conflicting Path ID | This document |
+------------+-----------------------------------+-----------------+
| 19 | 20 - Not supported path backup | This document |
+------------+-----------------------------------+-----------------+
| 19 | 21 - Non-empty path | This document |
+------------+-----------------------------------+-----------------+
9.4. Flags in the Multipath Capability TLV
IANA is requested to create a new sub-registry to manage the Flag
field of the MULTIPATH-CAP TLV, called “Flags in MULTIPATH-CAP TLV”.
New values are to be assigned by Standards Action [RFC8126]
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-12 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 13 | 0-flag: support for processing | This document |
| | MULTIPATH-OPPDIR-PATH TLV | |
+------------+-----------------------------------+-----------------+
| 14 | B-flag: support for processing | This document |
| | MULTIPATH-BACKUP TLV | |
+------------+-----------------------------------+-----------------+
| 15 | W-flag: support for processing | This document |
| | MULTIPATH-WEIGHT TLV | |
+------------+-----------------------------------+-----------------+
9.5. Flags in the Path Attribute Object
IANA is requested to create a new sub-registry to manage the Flag
field of the PATH-ATTRIBUTE object, called “Flags in PATH-ATTRIBUTE
Object”. New values are to be assigned by Standards Action [RFC8126]
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+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-12 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 13-15 | O-flag: Operational state | This document |
+------------+-----------------------------------+-----------------+
9.6. Flags in the Multipath Backup TLV
IANA is requested to create a new sub-registry to manage the Flag
field of the MULTIPATH-BACKUP TLV, called “Flags in MULTIPATH-BACKUP
TLV”. New values are to be assigned by Standards Action [RFC8126]
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-14 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 15 | B-flag: Pure backup | This document |
+------------+-----------------------------------+-----------------+
9.7. Flags in the Multipath Opposite Direction Path TLV
IANA is requested to create a new sub-registry to manage the flag
fields of the MULTIPATH-OPPDIR-PATH TLV, called “Flags in the
MULTIPATH-OPPDIR-PATH TLV”. New values are to be assigned by
Standards Action [RFC8126]
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-12 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 14 | L-flag: Link co-routed | This document |
+------------+-----------------------------------+-----------------+
| 15 | N-flag: Node co-routed | This document |
+------------+-----------------------------------+-----------------+
10. Security Considerations
None at this time.
11. Acknowledgement
Thanks to Dhruv Dhody for ideas and discussion. Thanks to Yuan
Yaping for review comments.
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12. Contributors
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
Chen Ran
ZTE
Email: chen.ran@zte.com.cn
13. References
13.1. Normative References
[I-D.draft-ietf-pce-pcep-color]
Rajagopalan, B., Beeram, V. P., Peng, S., Koldychev, M.,
and G. S. Mishra, "Path Computation Element Protocol(PCEP)
Extension for Color", Work in Progress, Internet-Draft,
draft-ietf-pce-pcep-color-02, 1 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
pcep-color-02>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "PCEP extension to support Segment Routing Policy
Candidate Paths", Work in Progress, Internet-Draft, draft-
ietf-pce-segment-routing-policy-cp-12, 24 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-12>.
[I-D.schmutzer-pce-cs-sr-policy]
Schmutzer, C., Filsfils, C., Ali, Z., Clad, F.,
Maheshwari, P., Rokui, R., Stone, A., Jalil, L., Peng, S.,
Saad, T., and D. Voyer, "Circuit Style Segment Routing
Policies", Work in Progress, Internet-Draft, draft-
schmutzer-pce-cs-sr-policy-02, 5 May 2022,
<https://datatracker.ietf.org/doc/html/draft-schmutzer-
pce-cs-sr-policy-02>.
[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>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
13.2. Informative References
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8745] Ananthakrishnan, H., Sivabalan, S., Barth, C., Minei, I.,
and M. Negi, "Path Computation Element Communication
Protocol (PCEP) Extensions for Associating Working and
Protection Label Switched Paths (LSPs) with Stateful PCE",
RFC 8745, DOI 10.17487/RFC8745, March 2020,
<https://www.rfc-editor.org/info/rfc8745>.
[RFC9059] Gandhi, R., Ed., Barth, C., and B. Wen, "Path Computation
Element Communication Protocol (PCEP) Extensions for
Associated Bidirectional Label Switched Paths (LSPs)",
RFC 9059, DOI 10.17487/RFC9059, June 2021,
<https://www.rfc-editor.org/info/rfc9059>.
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
Email: mkoldych@proton.me
Siva Sivabalan
Ciena Corporation
Email: ssivabal@ciena.com
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Tarek Saad
Juniper Networks, Inc.
Email: tsaad@juniper.net
Vishnu Pavan Beeram
Juniper Networks, Inc.
Email: vbeeram@juniper.net
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
Bhupendra Yadav
Ciena
Email: byadav@ciena.com
Shuping Peng
Huawei Technologies
Email: pengshuping@huawei.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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