Internet DRAFT - draft-koldychev-pce-multipath
draft-koldychev-pce-multipath
PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: August 20, 2021 Ciena Corporation
T. Saad
V. Beeram
Juniper Networks, Inc.
H. Bidgoli
Nokia
B. Yadav
Ciena
S. Peng
Huawei Technologies
February 16, 2021
PCEP Extensions for Signaling Multipath Information
draft-koldychev-pce-multipath-05
Abstract
Current PCEP standards allow only one intended and/or actual path to
be present in a PCEP report or update. Applications that require
multipath support such as SR Policy require an extension to allow
signaling multiple intended and/or actual paths within a single PCEP
message. This document introduces such an extension. Encoding of
multiple intended and/or actual paths is done by encoding multiple
Explicit Route Objects (EROs) and/or multiple Record Route Objects
(RROs). A special separator object is defined in this document, to
facilitate this. This mechanism is applicable to SR-TE and RSVP-TE
and is dataplane agnostic.
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
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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 August 20, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms and Abbreviations . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Signaling Multiple Segment-Lists of an SR Candidate-Path 4
3.2. Splitting of Requested Bandwidth . . . . . . . . . . . . 4
3.3. Providing Backup path for Protection . . . . . . . . . . 4
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 5
4.1. Multipath Capability TLV . . . . . . . . . . . . . . . . 5
4.2. Path Attributes Object . . . . . . . . . . . . . . . . . 6
4.3. Multipath Weight TLV . . . . . . . . . . . . . . . . . . 6
4.4. Multipath Backup TLV . . . . . . . . . . . . . . . . . . 7
4.5. Composite Candidate Path . . . . . . . . . . . . . . . . 8
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Signaling Multiple Paths for Loadbalancing . . . . . . . 10
5.2. Signaling Multiple Paths for Protection . . . . . . . . . 10
6. PCEP Message Extensions . . . . . . . . . . . . . . . . . . . 11
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. SR Policy Candidate-Path with Multiple Segment-Lists . . 11
7.2. Two Primary Paths Protected by One Backup Path . . . . . 13
7.3. Composite Candidate Path . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8.1. PCEP Object . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. PCEP TLV . . . . . . . . . . . . . . . . . . . . . . . . 14
8.3. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 14
8.4. Flags in the Multipath Capability TLV . . . . . . . . . . 15
8.5. Flags in the Path Attribute Object . . . . . . . . . . . 15
8.6. Flags in the Multipath Backup TLV . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
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12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] enables the communication between a Path Computation Client
(PCC) and a Path Control Element (PCE), or between two PCEs based on
the PCE architecture [RFC4655].
PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
of extensions to PCEP that enable active control of Multiprotocol
Label Switching Traffic Engineering (MPLS-TE) and Generalized MPLS
(GMPLS) tunnels. [RFC8281] describes the setup and teardown of PCE-
initiated LSPs under the active stateful PCE model, without the need
for local configuration on the PCC, thus allowing for dynamic
centralized control of a network.
PCEP Extensions for Segment Routing [RFC8664] specifies extensions to
the Path Computation Element Protocol (PCEP) that allow a stateful
PCE to compute and initiate Traffic Engineering (TE) paths, as well
as for a PCC to request a path subject to certain constraint(s) and
optimization criteria in SR networks.
Segment Routing Policy for Traffic Engineering
[I-D.ietf-spring-segment-routing-policy] 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 multipath information, and states that this will be
defined in another document.
This document defines the required extensions that allow the
signaling of multipath information via PCEP.
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.
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2.1. Terms and Abbreviations
The following terms are used in this document:
PCEP Tunnel:
The object identified by the PLSP-ID, see
[I-D.koldychev-pce-operational] for more details.
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 report/update 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 (containing multiple SR-ERO subobject), which prevents us from
encoding multiple Segment- Lists within the same SR Candidate-Path.
With the help of the protocol extensions defined in this document,
this limitation is overcome.
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 50 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 4.3 introduces a new TLV that carries the path weight that
allows for distribution of incoming traffic on to the multiple paths.
3.3. Providing Backup path for Protection
It is desirable for the PCE to compute and signal to the PCC a backup
path that is used to protect a primary path within the multipaths in
a given LSP.
Note that [RFC8745] specify the Path Protection association among
LSPs. The use of [RFC8745] with multipath is out of scope of this
document and is for future study.
When multipath is used, a backup path may protect one or more primary
paths. For this reason, primary and backup path identifiers are
needed to indicate which backup path(s) protect which primary
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path(s). Section 4.4 introduces a new TLV that carries the required
information.
4. Protocol Extensions
4.1. Multipath Capability TLV
We define the MULTIPATH-CAP TLV that MAY be present in the OPEN
object and/or the LSP object. The purpose of this TLV is two-fold:
1. From PCC: it tells how many multipaths per PCEP Tunnel, the PCC
can install in forwarding.
2. From PCE: it tells that the PCE supports this standard and how
many multipaths per PCEP Tunnel, the PCE can compute.
Only the first instance of this TLV can be processed, subsequent
instances SHOULD be ignored.
Section 5 specify the usage of this TLV with Open message (within the
OPEN object) and other PCEP messages (within the LSP 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Multipaths | Flags |B|W|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MULTIPATH-CAP TLV format
Type: TBD1 for "MULTIPATH-CAP" TLV.
Length: 4.
Number of Multipaths: the maximum number of multipaths per PCEP
Tunnel. The value 0 indicates unlimited number.
Flags: Following bits are defined:
W-flag: whether MULTIPATH-WEIGHT-TLV is supported.
B-flag: whether MULTIPATH-BACKUP-TLV is supported.
Unassigned bits are for future use. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
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4.2. 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 TBD2.
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 | O |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PATH-ATTRIB object format
Flags (32-bits): Following bits are assigned -
O (Operational - 3 bits): operational state of the path, same
values as the identically named field in the LSP object {{RFC8231}}.
Unassigned bits are for future use. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
Path ID: 4-octet identifier that identifies a path in the set of
multiple paths. It uniquely identifies a path (encoded in the ERO/
RRO) within the set of multiple paths under the PCEP LSP. Once a
path changes, a new Path ID is assigned.
TLVs that may be included in the PATH-ATTRIB object are described in
the following sections. Other optional TLVs could be defined by
future documents to be included within the PATH-ATTRIB object body.
4.3. Multipath Weight TLV
We define the MULTIPATH-WEIGHT TLV that MAY be present 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 3: MULTIPATH-WEIGHT TLV format
Type: TBD3 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".
4.4. Multipath Backup TLV
This document introduces a new MULTIPATH-BACKUP TLV that is optional
and can be present in the PATH-ATTRIB object.
This TLV is used to indicate the presence of a backup path that is
used for protection in case of failure of the primary path. The
format of the MULTIPATH-BACKUP TLV is:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path Count | Flags |B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup Path ID n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: MULTIPATH-BACKUP TLV format
Type: TBD4 for "MULTIPATH-BACKUP" TLV
Length: 4 + (N * 4) (where N is the Backup Path Count)
Backup Path Count: Number of backup path(s).
Flags (16 bits): a flag field. Currently a single flag "B bit" is
defined.
Unused flags MUST be set to zero while sending and ignored on
receipt.
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.
4.5. Composite Candidate Path
SR Policy Architecture [I-D.ietf-spring-segment-routing-policy]
defines the concept of a Composite Candidate Path. Unlike a Non-
Composite Candidate Path, which contains Segment Lists, the Composite
Candidate Path contains Colors of other policies. The traffic that
is steered into a Composite Candidate Path is split among the
policies that are identified by the Colors contained in the Composite
Candidate Path. The split can be either ECMP or UCMP by adjusting
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the weight of each color in the Composite Candidate Path, in the same
manner as the weight of each Segment List in the Non-Composite
Candidate Path is adjusted.
To signal the Composite Candidate Path, we make use of the COLOR TLV,
defined in [I-D.peng-pce-te-constraints]. For a Composite Candidate
Path, the COLOR TLV is included in the PATH-ATTRIB Object, thus
allowing each Composite Candidate Path to do ECMP/UCMP among SR
Policies or Tunnels 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 empty SR-ERO/SR-RRO object MUST be included as per the existing
RBNF, i.e., SR-ERO/SR-RRO MUST contain no sub-objects. If the head-
end receives a non-empty SR-ERO/SR-RRO, then it MUST send PCError
message with Error-Type 19 ("Invalid Operation") and Error-Value =
TBD8 ("Non-empty path").
See Section 7.3 for an example of the encoding.
5. Operation
When the PCC wants to indicate to the PCE that it wants to get
multipaths for a PCEP Tunnel, instead of a single path, it can do (1)
or both (1) and (2) of the following:
(1) Send the MULTIPATH-CAP TLV in the OPEN object during session
establishment. This applies to all PCEP Tunnels on the PCC, unless
overridden by PCEP Tunnel specific information.
(2) Additionally send the MULTIPATH-CAP TLV in the LSP object for a
particular PCEP Tunnel in the PCRpt or PCReq message. This applies
to the specified PCEP Tunnel and overrides the information from the
OPEN object.
When PCE computes the path for a PCEP Tunnel, it MUST NOT return more
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.
If the PCE supports this standard, then it MUST include the
MULTIPATH-CAP TLV in the OPEN object. This tells the PCC that it can
report multiple ERO/RRO objects per PCEP Tunnel to this PCE. If the
PCE does not include the MULTIPATH-CAP TLV in the OPEN object, then
the PCC MUST assume that the PCE does not support this standard and
fall back to reporting only a single ERO/RRO. The PCE MUST NOT
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include MULTIPATH-CAP TLV in the LSP object in any other PCEP message
towards the PCC and the PCC MUST ignore it if received.
The Path ID of each ERO/RRO MUST be unique within that LSP. 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 = TBD5
("Conflicting Path ID").
5.1. 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 or PCEP Tunnel.
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.
5.2. 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 Tunnel. 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 or PCEP Tunnel.
2. The MULTIPATH-BACKUP TLV MUST 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,
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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 if a given path has the B-flag set, then there MUST be some
other path within the same LSP that uses the given path as a backup.
If this condition is violated, then the PCEP speaker SHOULD send a
PCError message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = TBD6 ("No primary path for pure backup").
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 = TBD7 ("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>
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
[I-D.ietf-spring-segment-routing-policy].
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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:
<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>>
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, 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.
7.3. Composite Candidate Path
Consider the following Composite Candidate Path, taken from
[I-D.ietf-spring-segment-routing-policy].
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:
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<LSP PLSP_ID=100>
<ASSOCIATION>
<END-POINT>
<PATH-ATTRIB Path_ID=1 <WEIGHT-TLV Weight=W1> <COLOR-TLV Color=1>>
<SR-ERO (empty)>
<PATH-ATTRIB Path_ID=2 <WEIGHT-TLV Weight=W2> <COLOR-TLV Color=2>>
<SR-ERO (empty)>
8. IANA Considerations
8.1. 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 | |
+--------------+-------------+-------------------+-----------------+
| TBD2 | PATH-ATTRIB | 1 | This document |
+--------------+-------------+-------------------+-----------------+
8.2. 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 | | |
+------------+-----------------------------------+-----------------+
| TBD1 | MULTIPATH-CAP | This document |
+------------+-----------------------------------+-----------------+
| TBD3 | MULTIPATH-WEIGHT | This document |
+------------+-----------------------------------+-----------------+
| TBD4 | MULTIPATH-BACKUP | This document |
+------------+-----------------------------------+-----------------+
8.3. 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:
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+------------+-----------------------------------+-----------------+
| Error-Type | Error-Value | Reference |
+------------+-----------------------------------+-----------------+
| 10 | TBD5 - Conflicting Path ID | This document |
+------------+-----------------------------------+-----------------+
| 10 | TBD6 - No primary path for pure | This document |
| | backup | |
+------------+-----------------------------------+-----------------+
| 19 | TBD7 - Not supported path backup | This document |
+------------+-----------------------------------+-----------------+
| 19 | TBD8 - Non-empty path | This document |
+------------+-----------------------------------+-----------------+
8.4. 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".
Following bits are defined:
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-13 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 14 | B-flag: Backup support | This document |
+------------+-----------------------------------+-----------------+
| 15 | W-flag: Weighted ECMP support | This document |
+------------+-----------------------------------+-----------------+
8.5. 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".
Following bits are defined:
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-12 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 13-15 | O-flag: Operational state | This document |
+------------+-----------------------------------+-----------------+
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8.6. 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".
Following bits are defined:
+------------+-----------------------------------+-----------------+
| Bit | Description | Reference |
+------------+-----------------------------------+-----------------+
| 0-14 | Unassigned | This document |
+------------+-----------------------------------+-----------------+
| 15 | B-flag: Pure backup | This document |
+------------+-----------------------------------+-----------------+
9. Security Considerations
None at this time.
10. Acknowledgement
Thanks to Dhruv Dhody for ideas and discussion.
11. Contributors
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
12. References
12.1. Normative References
[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", draft-ietf-pce-segment-routing-policy-
cp-02 (work in progress), January 2021.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
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[I-D.koldychev-pce-operational]
Koldychev, M., Sivabalan, S., Negi, M., Achaval, D., and
H. Kotni, "PCEP Operational Clarification", draft-
koldychev-pce-operational-02 (work in progress), August
2020.
[I-D.peng-pce-te-constraints]
Peng, S., Xiong, Q., and F. Qin, "PCE TE Constraints for
Network Slicing", draft-peng-pce-te-constraints-04 (work
in progress), August 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
12.2. Informative References
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[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[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>.
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
Email: mkoldych@cisco.com
Siva Sivabalan
Ciena Corporation
Email: ssivabal@ciena.com
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
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Shuping Peng
Huawei Technologies
Email: pengshuping@huawei.com
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