Internet DRAFT - draft-ietf-pce-segment-routing-policy-cp
draft-ietf-pce-segment-routing-policy-cp
PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: 12 August 2024 Ciena Corporation
C. Barth
Juniper Networks, Inc.
S. Peng
Huawei Technologies
H. Bidgoli
Nokia
9 February 2024
PCEP Extensions for SR Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-14
Abstract
A Segment Routing (SR) Policy is a non-empty set of SR Candidate
Paths, which share the same <headend, color, endpoint> tuple. SR
Policy is modeled in PCEP as an Association of one or more SR
Candidate Paths. PCEP extensions are defined to signal additional
attributes of an SR Policy. The mechanism is applicable to all SR
forwarding planes (MPLS, SRv6, etc.).
Requirements Language
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.
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."
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This Internet-Draft will expire on 12 August 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. SR Policy Identifier . . . . . . . . . . . . . . . . . . 4
3.2. SR Policy Candidate Path Identifier . . . . . . . . . . . 4
3.3. SR Policy Candidate Path Attributes . . . . . . . . . . . 4
4. SR Policy Association . . . . . . . . . . . . . . . . . . . . 5
4.1. Association Parameters . . . . . . . . . . . . . . . . . 5
4.2. Association Information . . . . . . . . . . . . . . . . . 7
4.2.1. SR Policy Name TLV . . . . . . . . . . . . . . . . . 7
4.2.2. SR Policy Candidate Path Identifier TLV . . . . . . . 8
4.2.3. SR Policy Candidate Path Name TLV . . . . . . . . . . 9
4.2.4. SR Policy Candidate Path Preference TLV . . . . . . . 10
5. Other Mechanisms . . . . . . . . . . . . . . . . . . . . . . 10
5.1. SR Policy Capability TLV . . . . . . . . . . . . . . . . 10
5.2. Computation Priority TLV . . . . . . . . . . . . . . . . 11
5.3. Explicit Null Label Policy (ENLP) TLV . . . . . . . . . . 12
5.4. Invalidation TLV . . . . . . . . . . . . . . . . . . . . 13
5.5. Specified-BSID-only . . . . . . . . . . . . . . . . . . . 14
5.6. Stateless Operation . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. Association Type . . . . . . . . . . . . . . . . . . . . 15
6.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 16
6.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 16
6.4. TE-PATH-BINDING TLV Flag field . . . . . . . . . . . . . 17
6.5. SR Policy Candidate Path Protocol Origin field . . . . . 17
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
7.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.2. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
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9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
[RFC8664] specifies extensions that allow PCEP to work with basic SR-
TE paths. [RFC8697] introduces a generic mechanism to create a
grouping of LSPs, called an Association. [RFC9256] introduces the SR
Policy construct as a grouping of SR Candidate Paths.
This document extends [RFC8664] to support signaling SR Policy
Candidate Paths and their attributes. SR Policy is modeled in PCEP
as an Association, where the SR Candidate Paths are the members of
that Association. Thus the PCE can take computation and control
decisions about the Candidate Paths, with the additional knowledge
that these Candidate Paths belong to the same SR Policy.
2. Terminology
The following terminologies are used in this document:
Endpoint: The IPv4 or IPv6 endpoint address of the SR Policy in
question, as described in [RFC9256].
SRPA: SR Policy Association. PCEP ASSOCATION that describes the SR
Policy. Depending on discussion context, it refers to a PCEP
object or to a group of LSPs that belong to the Association.
Association Parameters: As described in [RFC8697], refers to the key
data, that uniquely identifies the Association in the network.
Association Information: As described in [RFC8697], refers to the
non-key information about the Association.
3. Overview
The SR Policy is represented by a new type of PCEP Association,
called the SR Policy Association (SRPA). The SR Candidate Paths of
an SR Policy are the PCEP LSPs within the same SRPA. The subject of
encoding multiple Segment Lists within an SR Policy Candidate Path is
described in [I-D.ietf-pce-multipath].
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The SRPA carries three pieces of information: SR Policy Identifier,
SR Policy Candidate Path Identifier, and SR Policy Candidate Path
Attribute(s).
Additional information is also carried outside of SRPA: Computation
Priority, Explicit Null Label Policy, Drop upon Invalid behavior, and
Specified-BSID-only.
3.1. SR Policy Identifier
SR Policy Identifier uniquely identifies the SR Policy within the
network. SR Policy Identifier MUST be the same for all SR Policy
Candidate Paths in the same SRPA. SR Policy Identifier MUST NOT
change for a given SR Policy Candidate Path during its lifetime. SR
Policy Identifier MUST be different for different SRPAs. SR Policy
Identifier consist of:
* Headend router where the SR Policy originates.
* Color of SR Policy.
* Endpoint of SR Policy.
3.2. SR Policy Candidate Path Identifier
SR Policy Candidate Path Identifier uniquely identifies the SR Policy
Candidate Path within the context of an SR Policy. SR Policy
Candidate Path Identifier MUST NOT change for a given LSP during its
lifetime. SR Policy Candidate Path Identifier MUST be different for
distinct Candidate Paths within the same SRPA. When these rules are
not satisfied, the PCEP speaker MUST send a PCErr message with Error-
Type = 26 "Association Error", Error Value = TBD8 "SR Policy
Candidate Path Identifier Mismatch". SR Policy Candidate Path
Identifier consist of:
* Protocol Origin.
* Originator.
* Discriminator.
3.3. SR Policy Candidate Path Attributes
SR Policy Candidate Path Attributes carry non-key information about
the Candidate Path and MAY change during the lifetime of the LSP. SR
Policy Candidate Path Attributes consist of:
* Preference.
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* Optionally, the SR Policy Candidate Path name.
* Optionally, the SR Policy name.
4. SR Policy Association
Two ASSOCIATION object types for IPv4 and IPv6 are defined in
[RFC8697]. The ASSOCIATION object includes "Association Type"
indicating the type of the association group. This document adds a
new Association Type (6) "SR Policy Association".
This Association Type is dynamic in nature, thus operator-configured
Association Range MUST NOT be set for this Association type and MUST
be ignored.
A PCEP speaker that supports the SRPA MUST send the ASSOC-Type-List
TLV, defined in [RFC8697] Section 4.1, containing the value (6),
corresponding to the SRPA Association Type. Otherwise the PCEP
speaker MUST assume that the remote PCEP peer does not support SRPA
and MUST NOT send the SRPA to that remote peer.
A given LSP MUST belong to at most one SRPA, since an SR Policy
Candidate Path cannot belong to multiple SR Policies. If a PCEP
speaker receives a PCEP message requesting to join more than one SRPA
for the same LSP, then the PCEP speaker MUST send a PCErr message
with Error-Type = 26 "Association Error", Error-Value = 7 "Cannot
join the association group".
4.1. Association Parameters
As per [RFC9256], an SR Policy is identified through the tuple
<headend, color, endpoint>. The headend is encoded as the
Association Source in the ASSOCIATION object and the color and
endpoint are encoded as part of Extended Association ID TLV.
The Association Parameters (see Section 2) consist of:
* Association Type: set to 6 "SR Policy Association".
* Association Source (IPv4/IPv6): set to the headend IP address.
* Association ID (16-bit): set to "1" (this 16-bit field is not
utilized, just set to a value).
* Extended Association ID TLV: encodes the Color and Endpoint of the
SR Policy.
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The Association Source MUST be set to the headend value of the SR
Policy, as defined in [RFC9256] Section 2.1. If the PCC receives a
PCInit message with the Association Source set not to the headend IP
but to some globally unique IP address that the headend owns, then
the PCC SHOULD accept the PCInit message and create the SRPA with the
Association Source that was sent in the PCInit message.
The 16-bit Association ID field in the ASSOCIATION object MUST be set
to the value of "1".
The Extended Association ID TLV MUST be included and it MUST be in
the following format:
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 = 31 | Length = 8 or 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Endpoint ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Association ID TLV format
Type: Extended Association ID TLV, type = 31.
Length: Either 8 or 20, depending on whether IPv4 or IPv6 address is
encoded in the Endpoint.
Color: SR Policy color value, non-zero as per [RFC9256] Section 2.1.
Endpoint: can be either IPv4 or IPv6. This value MAY be different
from the one contained in the END-POINTS object, or in the LSP-
IDENTIFIERS TLV.
If the PCEP speaker receives an SRPA object whose Association
Parameters do not follow the above specification, then the PCEP
speaker MUST send PCErr message with Error-Type = 26 "Association
Error", Error-Value = TBD7 "SR Policy Identifier Mismatch".
The purpose of choosing the Association Parameters in this way is to
guarantee that there is no possibility of a race condition when
multiple PCEP speakers want to create the same SR Policy at the same
time. By adhering to this format, all PCEP speakers come up with the
same Association Parameters independently of each other. Thus, there
is no chance that different PCEP speakers will come up with different
Association Parameters for the same SR Policy.
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The computed destination of the SR Policy Candidate Path MAY differ
from the Endpoint contained in the <headend, color, endpoint> tuple.
An example use case is to terminate the SR Policy before reaching the
Endpoint and have decapsulated traffic go the rest of the way to the
Endpoint node using the native IGP path(s). In this example, the
destination of the SR Policy Candidate Paths will be some node before
the Endpoint, but the Endpoint value is still used at the head-end to
steer traffic with that Endpoint IP into the SR Policy. Destination
of the SR Policy Candidate Path is signaled using the END-POINTS
object and/or LSP-IDENTIFIERS TLV, as per the usual PCEP procedures.
When neither END-POINTS object nor LSP-IDENTIFIERS TLV is present,
the PCEP speaker MUST extract the destination from the Endpoint field
in the SRPA Extended Association ID TLV.
4.2. Association Information
The SRPA object contains the following TLVs:
* SRPOLICY-POL-NAME TLV: (optional) encodes SR Policy Name string.
* SRPOLICY-CPATH-ID TLV: (mandatory) encodes SR Policy Candidate
Path Identifier.
* SRPOLICY-CPATH-NAME TLV: (optional) encodes SR Policy Candidate
Path string name.
* SRPOLICY-CPATH-PREFERENCE TLV: (optional) encodes SR Policy
Candidate Path preference value.
Of these new TLVs, SRPOLICY-CPATH-ID TLV is mandatory. When a
mandatory TLV is missing from the SRPA object, the PCEP speaker MUST
send a PCErr message with Error-Type = 6 "Mandatory Object Missing",
Error-Value = TBD6 "Missing SR Policy Mandatory TLV".
Unless specifically stated otherwise, the TLVs listed in the
following sub-sections are assumed to be single instance. Meaning,
only one instance of the TLV SHOULD be present in the object and only
the first instance of the TLV SHOULD be interpreted and subsequent
instances SHOULD be ignored.
4.2.1. SR Policy Name TLV
The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SR Policy Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRPOLICY-POL-NAME TLV format
Type: 56 for "SRPOLICY-POL-NAME" TLV.
Length: indicates the length of the value portion of the TLV in
octets and MUST be greater than 0. The TLV MUST be zero-padded so
that the TLV is 4-octet aligned.
SR Policy Name: SR Policy name, as defined in [RFC9256]. It SHOULD
be a string of printable ASCII characters, without a NULL terminator.
4.2.2. SR Policy Candidate Path Identifier TLV
The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proto. Origin | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Originator Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The SRPOLICY-CPATH-ID TLV format
Type: 57 for "SRPOLICY-CPATH-ID" TLV.
Length: 28.
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Protocol Origin: 8-bit value that encodes the protocol origin, as
specified in Section 6.5. Note that in PCInit messages, the Protocol
Origin is always set to "PCEP".
Originator ASN: Represented as 4 byte number, part of the originator
identifier, as specified in [RFC9256] Section 2.4. When sending
PCInit, the PCE is acting as the originator and therefore SHOULD set
this to an ASN that it belongs to.
Originator Address: Represented as 128 bit value where IPv4 address
are encoded in lowest 32 bits, part of the originator identifier, as
specified in [RFC9256] Section 2.4. When sending PCInit, the PCE is
acting as the originator and therefore SHOULD set this to an address
that it owns.
Discriminator: 32-bit value that encodes the Discriminator of the
Candidate Path. This is the field that mainly distinguishes
different SR Candidate Paths, coming from the same originator. It is
allowed to be any number in the 32-bit range.
4.2.3. SR Policy Candidate Path Name TLV
The SRPOLICY-CPATH-NAME TLV is an optional TLV for the SRPA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SR Policy Candidate Path Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The SRPOLICY-CPATH-NAME TLV format
Type: 58 for "SRPOLICY-CPATH-NAME" TLV.
Length: indicates the length of the value portion of the TLV in
octets and MUST be greater than 0. The TLV MUST be zero-padded so
that the TLV is 4-octet aligned.
SR Policy Candidate Path Name: SR Policy Candidate Path Name, as
defined in [RFC9256]. It SHOULD be a string of printable ASCII
characters, without a NULL terminator.
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4.2.4. SR Policy Candidate Path Preference TLV
The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPA
object. If the TLV is absent, then default Preference value is 100,
as per Section 2.7 of [RFC9256].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The SRPOLICY-CPATH-PREFERENCE TLV format
Type: 59 for "SRPOLICY-CPATH-PREFERENCE" TLV.
Length: 4.
Preference: Numerical preference of the Candidate Path.
5. Other Mechanisms
This section describes mechanisms that are standardized for SR
Policies in [RFC9256], but do not make use of the SRPA for signaling
in PCEP. Since SRPA is not used, there needs to be a separate
capability negotiation.
Unless specifically stated otherwise, the TLVs listed in the
following sub-sections are assumed to be single instance. Meaning,
only one instance of the TLV SHOULD be present in the object and only
the first instance of the TLV SHOULD be interpreted and subsequent
instances SHOULD be ignored.
5.1. SR Policy Capability TLV
The SRPOLICY-CAPABILITY TLV is an optional TLV for the OPEN object.
It is used at session establishment time to learn the other PCEP
peer's capabilities with respect to SR Policy.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |L|S|I|E|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 6: The SRPOLICY-CAPABILITY TLV format
Type: TBD4 for "SRPOLICY-CAPABILITY TLV.
Length: 4.
P-Flag: PCEP speaker supports the COMPUTATION-PRIORITY TLV with SR
Policy, see Section 5.2.
E-Flag: PCEP speaker supports the ENLP TLV with SR Policy, see
Section 5.3.
I-Flag: PCEP speaker supports INVALIDATION TLV with SR Policy, see
Section 5.4.
S-Flag: PCEP speaker supports "Specified-BSID-only" behavior with SR
Policy, see Section 5.5.
L-Flag: PCEP speaker supports stateless (PCReq/PCRep) operations with
SR Policy, see Section 5.6.
5.2. Computation Priority TLV
The COMPUTATION-PRIORITY TLV is an optional TLV for the LSP object.
It is used to signal the numerical computation priority, as specified
in Section 2.12 of [RFC9256]. If the TLV is absent from the LSP
object, a default Priority value of 128 is used.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The COMPUTATION-PRIORITY TLV format
Type: TBD1 for "COMPUTATION-PRIORITY" TLV.
Length: 4.
Priority: Numerical priority with which this LSP is to be recomputed
by the PCE upon topology change.
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5.3. Explicit Null Label Policy (ENLP) TLV
To steer an unlabeled IP packet into an SR policy, it is necessary to
create a label stack for that packet, and push one or more labels
onto that stack. The Explicit NULL Label Policy (ENLP) TLV is an
optional TLV used to indicate whether an Explicit NULL Label
[RFC3032] must be pushed on an unlabeled IP packet before any other
labels. The contents of this TLV are used by the SRPM as described
in section 4.1 of [RFC9256]. If an ENLP TLV is not present, the
decision of whether to push an Explicit NULL label on a given packet
is a matter of local configuration.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ENLP | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: The Explicit Null Label Policy (ENLP) TLV format
Type: TBD2 for "ENLP" TLV.
Length: 4.
ENLP (Explicit NULL Label Policy): Indicates whether Explicit NULL
labels are to be pushed on unlabeled IP packets that are being
steered into a given SR policy. This field has one of the following
values:
* 0: Reserved.
* 1: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet,
but do not push an IPv6 Explicit NULL label on an unlabeled IPv6
packet.
* 2: Push an IPv6 Explicit NULL label on an unlabeled IPv6 packet,
but do not push an IPv4 Explicit NULL label on an unlabeled IPv4
packet.
* 3: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet,
and push an IPv6 Explicit NULL label on an unlabeled IPv6 packet.
* 4: Do not push an Explicit NULL label.
* 5 - 255: Reserved.
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The ENLP reserved values may be used for future extensions and
implementations SHOULD ignore the ENLP TLV with these values. The
behavior signaled in this TLV MAY be overridden by local
configuration. The section 4.1 of [RFC9256] describes the behavior
on the headend for the handling of the explicit null label.
5.4. Invalidation TLV
The INVALIDATION TLV is an optional TLV for the LSP object. It is
used to control traffic steering into the LSP during the time when
the LSP is operationally down/invalid. In the context of SR Policy,
this TLV facilitates the "Drop upon invalid" behavior, specified in
Section 8.2 of [RFC9256]. Normally, if the LSP is down/invalid then
it stops attracting traffic and traffic that is originally destined
for that LSP is redirected somewhere else, such as via IGP or via
another LSP. The "Drop upon invalid" behavior specifies that the LSP
keeps attracting traffic and the traffic has to be dropped at the
head-end. Such an LSP is said to be "in drop state". While in the
drop state, the LSP operational state is "UP", as indicated by the
O-flag in the LSP object. However the ERO object MAY be empty, if no
valid path has been computed.
The INVALIDATION TLV is used in both directions between PCEP peers:
* PCE -> PCC: PCE specifies to the PCC under what conditions the LSP
should enter the drop state.
* PCC -> PCE: PCC reports under what conditions the LSP will enter
the drop state and the PCC also reports whether the LSP is
currently in the drop state and if so, for what reason.
Reasons for entering the drop state are represented by a set of
flags.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |V|P|F|G|
+-+-+-+-+-+-+-+-+
Figure 9: Invalidation Reasons Flags
* G: Generic - does not fit into any other categories below.
* F: First-hop resolution failure - head-end first hop resolution
has failed.
* P: Path computation failure - no path was computed for the LSP.
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* V: Verification failure - OAM/PM/BFD path verification has
indicated a breakage.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inval Reason | Drop Upon | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: The INVALIDATION TLV format
Type: TBD3 for "INVALIDATION" TLV.
Length: 4.
Inval Reason: contains "Invalidation Reasons Flags" which encode the
reason(s) why the LSP is currently invalidated. This field can be
set to non-zero values only by the PCC, it MUST be set to 0 by the
PCE and ignored by the PCC.
Drop Upon: contains "Invalidation Reasons Flags" for conditions that
SHOULD cause the LSP to enter drop state. This field can be set to
non-zero values by both PCC and PCE. When the G-flag is set, this
indicates that the LSP is to go into Drop upon invalid state for any
reason. I.e., when the PCE does not wish to distinguish any reason
for LSP invalidation and just simply wants it to always go into drop
state whenever the LSP is down. Note that when the G-flag is set,
the values of the other flags are irrelevant.
Note that out of all the "Invalidation Reasons Flags", only the
G-flag (Generic) MUST be supported. The other flags can simply be
ignored if they are not supported by the PCEP speaker. For example,
suppose the PCC only supports P-flag and G-flag. When this PCC
receives this TLV with Drop Upon set to 0x6 (P,F), then the PCC
responds with Drop Upon = 0x4 (P). When this PCC receives this TLV
with Drop Upon set to 0x7 (P,F,G), then the PCC responds with Drop
Upon = 0x5 (P,G).
5.5. Specified-BSID-only
Specified-BSID-only functionality is defined in Section 6.2.3 of
[RFC9256]. When specified-BSID-only is enabled for a particular
binding SID, it means that the given binding SID is required to be
allocated and programmed for the LSP to be operationally up. If the
binding SID cannot be allocated or programmed for some reason, then
the LSP must stay down.
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To signal specified-BSID-only, a new bit: S (Specified-BSID-only) is
allocated in the "TE-PATH-BINDING TLV Flag field" of the TE-PATH-
BINDING TLV. When this bit is set for a particular BSID, it means
that the BSID follows the Specified-BSID-only behavior. It is
possible to have a mix of BSIDs for the same LSP: some with S=1 and
some with S=0.
5.6. Stateless Operation
[RFC8231] Section 5.8.2, allows delegation of an LSP in operationally
down state, but at the same time mandates the use of PCReq before
sending PCRpt. This document modifies the procedure of [RFC8231]
Section 5.8.2, for SR Policies we make sending of PCReq before PCRpt
OPTIONAL. Thus, when a PCC wants to delegate an SR Policy LSP, it
MAY proceed directly to sending PCRpt, without first sending PCReq
and waiting for PCRep. This has the advantage of reducing the number
of PCEP messages and simplifying the implementation.
Furthermore, a PCEP speaker is not required to support PCReq/PCRep at
all for SR Policies. The PCEP speaker can indicate support for
PCReq/PCRep via the "L-Flag" in the SRPOLICY-CAPABILITY TLV (See
Section 5.1). When this flag is cleared, or when the SRPOLICY-
CAPABILITY TLV is absent, the given peer SHOULD NOT be sent PCReq/
PCRep messages for SR Policy LSPs. Conversely when this flag is set,
the peer can receive and process PCReq/PCRep messages for SR Policy
LSPs.
The above applies only to SR Policy LSPs and does not affect other
LSP types, such as RSVP-TE LSPs. For other LSP types, [RFC8231]
Section 5.8.2 continues to apply.
6. IANA Considerations
6.1. Association Type
This document defines a new association type: SR Policy Association.
IANA is requested to make the following codepoint assignment in the
"ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
Computation Element Protocol (PCEP) Numbers" registry:
+-----------+-------------------------------------------+-----------+
| Type | Name | Reference |
+-----------+-------------------------------------------+-----------+
| 6 | SR Policy Association | This.I-D |
+-----------+-------------------------------------------+-----------+
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6.2. PCEP TLV Type Indicators
This document defines four new TLVs for carrying additional
information about SR Policy and SR Candidate Paths. IANA is
requested to make the assignment of a new value for the existing
"PCEP TLV Type Indicators" registry as follows:
+-----------+-------------------------------------------+-----------+
| Value | Description | Reference |
+-----------+-------------------------------------------+-----------+
| 56 | SRPOLICY-POL-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 57 | SRPOLICY-CPATH-ID | This.I-D |
+-----------+-------------------------------------------+-----------+
| 58 | SRPOLICY-CPATH-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 59 | SRPOLICY-CPATH-PREFERENCE | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD1 | COMPUTATION-PRIORITY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD2 | EXPLICIT-NULL-LABEL-POLICY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD3 | INVALIDATION | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD4 | SRPOLICY-CAPABILITY | This.I-D |
+-----------+-------------------------------------------+-----------+
6.3. PCEP Errors
This document defines one new Error-Value within the "Mandatory
Object Missing" Error-Type and two new Error-Values within the
"Association Error" Error-Type. IANA is requested to allocate new
error values within the "PCEP-ERROR Object Error Types and Values"
sub-registry of the PCEP Numbers registry, as follows:
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+------------+------------------+-----------------------+-----------+
| Error-Type | Meaning | Error-value | Reference |
+------------+------------------+-----------------------+-----------+
| 6 | Mandatory Object | | [RFC5440] |
| | Missing | | |
+------------+------------------+-----------------------+-----------+
| | | TBD6: Missing SR | This.I-D |
| | | Policy Mandatory TLV | |
+------------+------------------+-----------------------+-----------+
| 26 | Association | | [RFC8697] |
| | Error | | |
+------------+------------------+-----------------------+-----------+
| | | TBD7: SR Policy | This.I-D |
| | | Identifers Mismatch | |
+------------+------------------+-----------------------+-----------+
| | | TBD8: SR Policy | This.I-D |
| | | Candidate Path | |
| | | Identifier Mismatch | |
+------------+------------------+-----------------------+-----------+
6.4. TE-PATH-BINDING TLV Flag field
IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV
Flag field" sub-registry of the PCEP Numbers registry, as follows:
+------------+------------------------------------------+-----------+
| Bit position | Description | Reference |
+--------------+----------------------------------------+-----------+
| TBD9 | S (Specified-BSID-only) | This.I-D |
+--------------+----------------------------------------+-----------+
6.5. SR Policy Candidate Path Protocol Origin field
This document requests IANA to maintain a new registry under "Segment
Routing Parameters" registry group. New values are to be assigned by
"Standards Action" [RFC8126]. The new registry is called "SR Policy
Protocol Origin". The registry contains the following codepoints,
with initial values, to be assigned by IANA with the reference set to
this document:
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+------------+------------------------------------------------------+
| Value | Description |
+--------------+----------------------------------------------------+
| 0 | Reserved (not to be used) |
+--------------+----------------------------------------------------+
| 1-9 | Unassigned |
+--------------+----------------------------------------------------+
| 10 | PCEP |
+--------------+----------------------------------------------------+
| 11-19 | Unassigned |
+--------------+----------------------------------------------------+
| 20 | BGP SR Policy |
+--------------+----------------------------------------------------+
| 21-29 | Unassigned |
+--------------+----------------------------------------------------+
| 30 | Configuration (CLI, YANG model via NETCONF, etc.) |
+--------------+----------------------------------------------------+
| 31-250 | Unassigned |
+--------------+----------------------------------------------------+
| 251 - 255 | Private Use (not to be assigned by IANA) |
+--------------+----------------------------------------------------+
7. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
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".
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7.1. Cisco
* Organization: Cisco Systems
* Implementation: IOS-XR PCC and PCE.
* Description: All features supported except Computation Priority,
Explicit NULL and Invalidation Drop.
* Maturity Level: Production.
* Coverage: Full.
* Contact: mkoldych@cisco.com
7.2. Juniper
* Organization: Juniper Networks
* Implementation: PCC and PCE.
* Description: Everything in -05 except SR Policy Name TLV and SR
Policy Candidate Path Name TLV.
* Maturity Level: Production.
* Coverage: Partial.
* Contact: cbarth@juniper.net
8. Security Considerations
This document defines one new type for ASSOCIATION object, which does
not add any new security concerns beyond those discussed in
[RFC5440], [RFC8231], [RFC8664] and [RFC8697] in itself.
The information carried in the SRPA object, as per this document is
related to SR Policy. It often reflects information that can also be
derived from the SR Database, but association provides a much easier
grouping of related LSPs and messages. The SRPA could provide an
adversary with the opportunity to eavesdrop on the relationship
between the LSPs. Thus securing the PCEP session using Transport
Layer Security (TLS) [RFC8253], as per the recommendations and best
current practices in [RFC7525], is RECOMMENDED.
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9. Acknowledgement
Would like to thank Stephane Litkowski, Boris Khasanov, Abdul Rehman,
Alex Tokar, Praveen Kumar and Tom Petch for review and suggestions.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<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>.
[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>.
[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>.
[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.
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[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
10.2. Informative References
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7525, DOI 10.17487/RFC7525, May 2015,
<https://www.rfc-editor.org/info/rfc7525>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
Extensions for Signaling Multipath Information", Work in
Progress, Internet-Draft, draft-ietf-pce-multipath-10, 16
January 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-pce-multipath-10>.
Appendix A. Contributors
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Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing, 10095
China
Email: chengli13@huawei.com
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
2000 Innovation Drive
Kanata Ontario K2K 3E8
Canada
Email: mkoldych@proton.me
Siva Sivabalan
Ciena Corporation
385 Terry Fox Dr.
Kanata Ontario K2K 0L1
Canada
Email: ssivabal@ciena.com
Colby Barth
Juniper Networks, Inc.
Email: cbarth@juniper.net
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Shuping Peng
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: pengshuping@huawei.com
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
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