Internet DRAFT - draft-lin-idr-sr-epe-over-l2bundle
draft-lin-idr-sr-epe-over-l2bundle
IDR Working Group C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track Z. Li
Expires: July 10, 2024 China Mobile
R. Pang
China Unicom
M. Chen
New H3C Technologies
January 10, 2024
Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle
draft-lin-idr-sr-epe-over-l2bundle-04
Abstract
There are deployments where the Layer 3 interface on which a BGP
peer session is established is a Layer 2 interface bundle. In order
to allow BGP-EPE to control traffic flows on individual member links
of the underlying Layer 2 bundle, BGP Peering SIDs need to be
allocated to individual bundle member links, and advertisement of
such BGP Peering SIDs in BGP-LS is also required. This document
describes how to support Segment Routing BGP Egress Peer Engineering
over Layer 2 bundle.
Status of this Memo
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This Internet-Draft will expire on July 10, 2024.
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Table of Contents
1. Introduction...................................................2
1.1. Requirements Language.....................................3
2. Problem Statement..............................................3
3. Peer Adjacency Segment for L2 Bundle Member Link...............4
3.1. Advertising in BGP-LS.....................................4
3.2. MPLS-SR Data Plane: L2 Bundle Member PeerAdj SID TLV......5
3.3. SRv6 Data Plane: SRv6 End.X SID TLV.......................6
4. Example........................................................6
4.1. Link Attributes on SR-MPLS Data Plane.....................7
4.2. Link Attributes on SRv6 Data Plane........................8
5. Considerations of Reusing Existing PeerAdj SID TLV.............8
6. Manageability Considerations...................................9
7. Security Considerations........................................9
8. IANA Considerations............................................9
9. References.....................................................9
9.1. Normative References......................................9
9.2. Informative References...................................10
Acknowledgements.................................................10
Authors' Addresses...............................................11
1. Introduction
Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through an ordered list of instructions called
"segments". Segment Routing can be instantiated on both MPLS and
IPv6 data planes, which are referred to as SR-MPLS and SRv6.
BGP Egress Peer Engineering (BGP-EPE) allows an ingress Provider
Edge (PE) router within the domain to use a specific egress PE and a
specific external interface/neighbor to reach a particular
destination.
The SR architecture [RFC8402] defines three types of BGP Peering
Segments that may be instantiated at a BGP node:
o Peer Node Segment (PeerNode SID): instruction to steer to a
specific peer node
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o Peer Adjacency Segment (PeerAdj SID): instruction to steer over a
specific local interface towards a specific peer node
o Peer Set Segment (PeerSet SID): instruction to load-balance to a
set of specific peer nodes
[RFC9087] illustrates a centralized controller-based BGP-EPE
solution involving SR path computation using the BGP Peering
Segments. A centralized controller learns the BGP Peering SIDs via
Border Gateway Protocol - Link State (BGP-LS) and then uses this
information to program a BGP-EPE policy. [RFC9086] defines the
extension to BGP-LS for advertisement of BGP Peering Segments along
with their BGP peering node information.
There are deployments where the Layer 3 interface on which a BGP
peer session is established is a Layer 2 interface bundle (L2
Bundle), for instance, a Link Aggregation Group (LAG) [IEEE802.1AX].
BGP-EPE may wish to control traffic flows on individual member links
of the underlying Layer 2 bundle. In order to do so, BGP Peering
SIDs need to be allocated to individual bundle member links, and
advertisement of such BGP Peering SIDs in BGP-LS is also required.
This document describes how to support Segment Routing BGP Egress
Peer Engineering over Layer 2 bundle.
1.1. 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.
2. Problem Statement
In the network depicted in Figure 1, B and C establish BGP peer
session on a Layer 2 bundle. Assume that, the link delays of the
members are different because they are over different transport
paths, and member link 1 has the lowest delay.
The operator of AS1 wishes to apply a BGP-EPE policy to steer the
time-sensitive traffic from AS1 to AS2 via member link 1 of the
Layer 2 bundle.
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L2 Bundle +--------+
/---member 1---\ | |
--+---member 2---+--C AS2 |
+--------+ / \---member 3---/ | |
| |/ +--------+
A AS1 B
| |\ +--------+
+--------+ \ | |
--------------------D AS3 |
| |
+--------+
Figure 1: BGP-EPE over L2 Bundle
The existing PeerAdj SID can be allocated to the Layer 3 interface
between B and C, which is a Layer 2 interface bundle. If steered by
that PeerAdj SID, the traffic will be forwarded by load balancing
among all the bundle member links. So, the existing mechanism cannot
meet the requirement of steering traffic flows via individual member
link.
3. Peer Adjacency Segment for L2 Bundle Member Link
This document extends Peer Adjacency Segments to be allocated to the
individual member links of the Layer 2 interface bundle.
The semantics of a Peer Adjacency Segment for L2 Bundle Member Link
are:
o SR operation: NEXT.
o Next-Hop: forwarding across the bundle member link, which the
segment is associated with, to the peer connected through the
parent L3 interface.
On the SR-MPLS data plane, Peer Adjacency Segments for L2 Bundle
Member Links are instantiated as MPLS labels. On the SRv6 data
plane, Peer Adjacency Segments for L2 Bundle Members are
instantiated as SRv6 End.X SIDs.
3.1. Advertising in BGP-LS
BGP peering segments are generally advertised in BGP-LS from a BGP
node along with its peering topology information, in order to enable
computation of efficient BGP-EPE policies and strategies.
When advertising Peer Adjacency Segments for L2 Bundle Member Links
in BGP-LS, they can be carried in the sub-TLVs of L2 Bundle Member
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Attributes TLVs [RFC9085]. Derived from IS-IS advertisements of L2
Bundle [RFC8668], each L2 Bundle Member Attributes TLV identifies an
L2 Bundle Member link, which in turn is associated with a parent L3
link. The L3 link is described by the Link NLRI, and the L2 Bundle
Member Attributes TLV is associated with the Link NLRI. The L2
Bundle Member Attributes TLV MAY include sub-TLVs that describe
attributes associated with the bundle member.
In order to advertise Peer Adjacency Segments for L2 Bundle Member
Links in BGP-LS, a BGP-LS Link NLRI is advertised to describe the
parent L3 link to the BGP peer, which is similar with advertising a
PeerAdj SID for the parent L3 link as specified in Section 5.2 of
[RFC9086]. Then, multiple L2 Bundle Member Attributes TLVs are
included in the Link Attribute TLVs associated with the parent L3
link, each identifying an L2 Bundle member link. The L2 Bundle
Member Attributes TLV MUST carry the following sub-TLVs:
o SR-MPLS data plane: L2 Bundle Member PeerAdj SID TLV (Type-TBD,
defined in Section 3.2) contains a Peer Adjacency Segment for the
associated L2 Bundle member link.
o SRv6 data plane: SRv6 End.X SID TLV (Type-1106) [RFC9514]
contains a Peer Adjacency Segment for the associated L2 Bundle
member link.
Besides, the L2 Bundle Member Attributes TLV MAY also carry other
link attributes describing the associated L2 Bundle member link,
such as administrative group (color), link bandwidth, and link
delay.
When a BGP peer session is established over a Layer 2 interface
bundle, an implementation MAY allocate one or more Peer Adjacency
Segments for each member link and advertise them in BGP-LS,
according to its local configuration and the behavior defined in
this document. The inclusion of a L2 Bundle Member Attributes TLV
implies that the identified link is a member of the L2 bundle and
that the member link is operationally up. If any member link fails,
an implementation MUST withdraw the L2 Bundle Member Attributes TLV
in BGP-LS, along with the Peer Adjacency Segments for the failed
member link.
3.2. MPLS-SR Data Plane: L2 Bundle Member PeerAdj SID TLV
On the SR-MPLS data plane, L2 Bundle Member PeerAdj SID TLV is
defined to advertise Peer Adjacency Segments for L2 Bundle member
links. It has the following format:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD.
o Length: variable. Valid values are either 7 or 8 based on
whether the encoding is done as a SID Index or a label.
o Flags: one octet of flags. Same as the Flags field of BGP Peering
SIDs TLV, as described in Section 5 of [RFC9086].
o Weight: 1 octet. The value represents the weight of the SID for
the purpose of load balancing.
o SID/Index/Label. According to the TLV length and the V- and L-
Flag settings, it contains either:
- A 3-octet local label where the 20 rightmost bits are used
for encoding the label value. In this case, the V- and L-
Flags MUST be SET.
- A 4-octet index defining the offset in the Segment Routing
Global Block (SRGB) [RFC8402] advertised by this router. In
this case, the SRGB MUST be advertised using the extensions
defined in [RFC9085].
3.3. SRv6 Data Plane: SRv6 End.X SID TLV
On the SRv6 data plane, SRv6 End.X SID TLV (Type-1106) [RFC9514] can
be used to advertise Peer Adjacency Segments for L2 Bundle member
links.
4. Example
Take the allocating and advertising of Peer Adjacency Segments on
Node B in Figure 1 as an example.
B allocates a PeerAdj SID for the Layer 2 interface bundle to peer
C, along with a PeerAdj SID for each member link. B programs its
forwarding table accordingly:
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+===============================+====================+
| PeerAdj SID | Outgoing Interface |
+---------------+---------------+ |
| IF on SR-MPLS | IF on SRv6 | |
| Data Plane | Data Plane | |
+===============+===============+====================+
| 1010 | A::A0 | L2 Bundle to C |
+---------------+---------------+--------------------+
| 1011 | A::A1 | Member link 1 to C |
+---------------+---------------+--------------------+
| 1012 | A::A2 | Member link 2 to C |
+---------------+---------------+--------------------+
| 1013 | A::A3 | Member link 3 to C |
+---------------+---------------+--------------------+
B signals the related BGP-LS NLRI to the BGP-EPE controller, which
is described in the following.
Descriptors:
o Local Node Descriptors (B's router-ID, ASN-AS1)
o Remote Node Descriptors (C's router-ID, ASN-AS2)
o Link Descriptors (Link Local/Remote Identifiers describing the
Layer 2 bundle, IPv4 or IPv6 Interface Address, IPv4 or IPv6
Neighbor Address)
4.1. Link Attributes on SR-MPLS Data Plane
Attributes:
o PeerAdj SID TLV (Label-1010)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 1)
* L2 Bundle Member PeerAdj SID TLV (Label-1011)
* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 1)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 2)
* L2 Bundle Member PeerAdj SID TLV (Label-1012)
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* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 2)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 3)
* L2 Bundle Member PeerAdj SID TLV (Label-1013)
* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 3)
4.2. Link Attributes on SRv6 Data Plane
Attributes:
o SRv6 End.X SID TLV (SID-A::A0)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 1)
* SRv6 End.X SID TLV (SID-A::A1)
* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 1)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 2)
* SRv6 End.X SID TLV (SID-A::A2)
* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 2)
o L2 Bundle Member Attribute TLV (Link Local Identifier describing
the member link 3)
* SRv6 End.X SID TLV (SID-A::A3)
* (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
member link 3)
5. Considerations of Reusing Existing PeerAdj SID TLV
The solution in Section 3 defines a new TLV to advertise Peer
Adjacency Segment for L2 Bundle member links on SR-MPLS data plane.
It may also be possible to reuse the PeerAdj SID TLV defined in
[RFC9086]. In this way, the PeerAdj SID TLV will be extended to be
included as a sub-TLV of the L2 Bundle Member Attributes TLV.
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6. Manageability Considerations
The manageability considerations described in [RFC9552] and
[RFC9086] also apply to this document.
The operator MUST be provided with the options of configuring,
enabling, and disabling the advertisement of Peer Adjacency Segment
for L2 Bundle member links, as well as control of which information
is advertised to which internal or external peer.
7. Security Considerations
The security considerations described in [RFC9552] and [RFC9086]
also apply to this document.
This document does not introduce any new security consideration.
8. IANA Considerations
This document defines a new BGP-LS Attribute TLV in the "BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs"
registry.
+================+==============================
| TLV Code Point | Description |
+================+==============================+
| TBA | L2 Bundle Member PeerAdj SID |
+----------------+------------------------------+
9. References
9.1. 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>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085, DOI
10.17487/RFC9085, August 2021, <https://www.rfc-
editor.org/info/rfc9085>.
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
[RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
Bernier, D., and B. Decraene, "Border Gateway Protocol -
Link State (BGP-LS) Extensions for Segment Routing over
IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
2023, <https://www.rfc-editor.org/info/rfc9514>.
[RFC9552] K. Talaulikar, "Distribution of Link-State and Traffic
Engineering Information Using BGP", RFC 9552, DOI
10.17487/RFC9552, December 2023, <https://www.rfc-
editor.org/info/rfc9552>.
9.2. Informative References
[IEEE802.1AX] IEEE, "IEEE Standard for Local and metropolitan area
networks -- Link Aggregation", IEEE 802.1AX,
<https://ieeexplore.ieee.org/document/7055197>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
[RFC9087] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
and D. Afanasiev, "Segment Routing Centralized BGP Egress
Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
2021, <https://www.rfc-editor.org/info/rfc9087>.
Acknowledgements
The authors would like to thank Sasha Vainshtein for his review and
comments of this document.
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Authors' Addresses
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Zhenqiang Li
China Mobile
China
Email: lizhenqiang@chinamobile.com
Ran Pang
China Unicom
China
Email: pangran@chinaunicom.cn
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
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