BGP SR Policy Extensions for metric
draft-ietf-idr-sr-policy-metric-00
| Document | Type | Active Internet-Draft (idr WG) | |
|---|---|---|---|
| Authors | KaZhang , Jie Dong , Ketan Talaulikar | ||
| Last updated | 2023-12-18 | ||
| Replaces | draft-zhang-idr-sr-policy-metric | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-idr-sr-policy-metric-00
Network Working Group K. Zhang
Internet-Draft J. Dong
Intended status: Standards Track Huawei
Expires: 20 June 2024 K. Talaulikar
Cisco Systems
18 December 2023
BGP SR Policy Extensions for metric
draft-ietf-idr-sr-policy-metric-00
Abstract
SR Policy candidate paths can be represented in BGP UPDATE messages.
BGP can then be used to propagate the SR Policy candidate paths to
the headend nodes in the network. After SR Policy is installed on
the ingress node, the packets can be steered into SR Policy through
route selection. Therefore, route selection may be performed on the
ingress node of the SR Policy. If there are multiple routes to the
same destination, the route selection node can select routes based on
the local policy. The local policy may use the IGP metric of the
selected path, which is the IGP Metric of the SR Policy. Thus the
BGP UPDATE message needs to carry the metric of each segment list of
the SR Policy Candidate Path, which can be used in path selection of
routing.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in 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."
Zhang, et al. Expires 20 June 2024 [Page 1]
Internet-Draft BGP SR Policy Extensions for metric December 2023
This Internet-Draft will expire on 20 June 2024.
Copyright Notice
Copyright (c) 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SR Policy and Tunnel Encapsulation Attribute Update . . . . . 3
4.1. Metric sub-TLV . . . . . . . . . . . . . . . . . . . . . 4
5. Metric process of SR Policy segment list . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7.1. New Registry: Metric Sub-TLV . . . . . . . . . . . . . . 6
7.2. New Registry: Metric Type . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[I-D.ietf-idr-segment-routing-te-policy]defines SR Policy and Tunnel
Encapsulation Attributes. It defines the segment list of the SR
policies. Each segment list of an SR Policy is a segment routing
path, which may be calculated by path computation element and
delivered to the head node of the device by BGP Update Message. On
the ingress node, when steering traffic to an SR Policy, the ingress
node may need to select between multiple SR Policy paths. And the
selection policy may also need the path metric information.
Therefore, BGP needs to carry the metric of each path when delivering
the segment list of the SR Policy through Update messages to
facilitate route selection on the device.
Zhang, et al. Expires 20 June 2024 [Page 2]
Internet-Draft BGP SR Policy Extensions for metric December 2023
2. Terminology
The following terminology is used in this document.
SR Policy: An ordered list of segments.
Candidate Path: the unit for signaling of an SR Policy to a headend
via protocol PCEP or BGP, which is defined in
[I-D.ietf-pce-segment-routing-policy-cp] and
[I-D.ietf-idr-segment-routing-te-policy].
SRPM: SR Policy Module.
3. Motivation
In route selection scenarios, the metric of the SR Policy segment
list may be required.
The specific scenarios are as follows:
+--+ +--+ +---+
_ _ _ _ _|P1|_ _ _ _ _|P2|_ _ _ _ _|PE2|_ _ _ _
| +--+ +--+ +---+ |
| |
+---+ +---+ +---+
|CE1|_ _ _ _ |PE1| |CE1|
+---+ +---+ +---+
| +--+ +--+ +---+ |
|_ _ _ _ _|P3|_ _ _ _ _|P4|_ _ _ _ _|PE3|_ _ _ _|
+--+ +--+ +---+
On PE1, the route prefix to CE1 has two different next hop, PE2 and
PE3. The next hop to PE1 uses an SR Policy1 on PE1, the endpoint of
SR Policy1 is PE2. The next hop to PE2 uses an SR Policy2 on PE1,
the endpoint of SR Policy2 is PE3. The prefix to CE1 wants to choose
a next hop based on the IGP metric of the route PE1 to PE2 and PE1
and PE3, which uses SR Policy1 and SR Policy2. Thus, BGP needs to
pass the IGP metric of SR Policy segment list on PE1.
4. SR Policy and Tunnel Encapsulation Attribute Update
As the metric is defined, the tunnel attribute encapsulation of the
BGP SR Policy needs to be updated.
The SR Policy Encoding structure is as follows:
Zhang, et al. Expires 20 June 2024 [Page 3]
Internet-Draft BGP SR Policy Extensions for metric December 2023
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Metric
Segment
Segment
....
....
Where metric indicates the metric for the segment list.
4.1. Metric sub-TLV
A new sub-TLV called Metric sub-TLV is defined. Metric sub-TLV
specifies the metric of an SR policy Segment List. Each sub-TLV is
encoded as shown in Figure 1. More than one metric Sub-TLVs may be
present in one Segment List to refer to the metric values of
different metric types.
Zhang, et al. Expires 20 June 2024 [Page 4]
Internet-Draft BGP SR Policy Extensions for metric December 2023
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Metric Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Metric Sub-TLV
* Type: Metric, 1 octet, TBD.
* Length: 6 octets.
* Metric Type: 1-octet field which identifies the type of the metric
being used. The metric-type code points are listed in Section 8.2.
* Flags: None are defined at this stage. Flags SHOULD be set to zero
on transmission and MUST be ignored on receipt.
* Metric Value: 4-octet value which indicates the metric of the
computed path.
5. Metric process of SR Policy segment list
When the SR Policy headend gets the SR Policy segment list with the
metric field, the metric may be of any of the defined types: (IGP
metric, Min Unidirection Link delay, TE metric, Hop Count, or SD List
length).
The rules for processing SR Policy metrics are as follows:
1. The type of metric to use is determined by the local policy,
which can be user-configured. For example, the user specifies
the IGP metric as local policy.
2. The metric of the Active Candidate Path is used as the metric
of the SR Policy.
3. The metric of the Active Candidate Path uses the maximum
metric value of the specified metric type in all segment lists.
Zhang, et al. Expires 20 June 2024 [Page 5]
Internet-Draft BGP SR Policy Extensions for metric December 2023
Example:
SR Policy: (Headend:1::1, Color: 2, EndPoint: 2::2)
Candidate path preference: 200
Segment list 1: (IGP metric: 20, Link delay: 10, TE metric: 10)
Segment list 2: (IGP metric: 30, Link delay: 20, TE metric: 15)
Candidate Path preference: 100
Segment list 1: (IGP metric: 40, Link delay: 20, TE metric: 20)
Segment list 2: (IGP metric: 30, Link delay: 10, TE metric: 15)
Local policy: IGP metric
Active candidate path: preference 200
Active candidate path metric: 30, which is the maximum IGP metric
of all segment lists in the candidate path.
6. Acknowledgements
TBD.
7. IANA Considerations
7.1. New Registry: Metric Sub-TLV
This document defines a new Sub-TLV in requests registries "SR Policy
List Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy]:
Value Description Reference
---------------------- ---------------------------- --------------
TBD Metric This document
Figure 2: Metric sub-TLV
7.2. New Registry: Metric Type
This document requests IANA to maintain a new registry under the "BGP
Tunnel Encapsulation" registry. The new registry is called "Metric
Type" and contains the codepoints allocated to the "metric type"
field defined in Section 4.1. The registry contains the following
codepoints, with initial values, to be assigned by IANA with the
reference set to this document:
Zhang, et al. Expires 20 June 2024 [Page 6]
Internet-Draft BGP SR Policy Extensions for metric December 2023
+------------+------------------------------------------+
| Code Point | Metric Type |
+------------+------------------------------------------+
| 0 | IGP Metric |
| 1 | Min Unidirectional Link Delay [RFC7471] |
| 2 | TE Metric [RFC3630] |
| 3 | Hop Count (refer [RFC5440]) |
| 4 | SID List Length |
| 5-250 | Unassigned |
| 251-255 | Private Use (not to be assigned by IANA) |
+------------+------------------------------------------+
Figure 3: Metric Type Code Point
8. Security Considerations
These extensions to the BGP SR Policy do not add any new security
issues to the existing protocol.
9. References
[I-D.ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Segment Routing Policies using
BGP Link-State", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-ls-sr-policy-03, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-03>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
[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>.
Zhang, et al. Expires 20 June 2024 [Page 7]
Internet-Draft BGP SR Policy Extensions for metric December 2023
[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>.
[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>.
Authors' Addresses
Ka Zhang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: zhangka@huawei.com
Jie Dong
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: jie.dong@huawei.com
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
Zhang, et al. Expires 20 June 2024 [Page 8]