Internet DRAFT - draft-lp-spring-sr-policy-reverse-path
draft-lp-spring-sr-policy-reverse-path
SPRING WG Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE Corporation
Expires: July 31, 2021 January 27, 2021
SR Policy for Reverse Path
draft-lp-spring-sr-policy-reverse-path-00
Abstract
This document introduces a method of dynamically configuring the
return path for an SR path.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. SR Policy for Bidirectional Path . . . . . . . . . . . . . . 2
2.1. BGP Extensions for Advertising Segment List . . . . . . . 3
2.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Difference from Path Segment . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Echo-BFD [RFC5880] can be used to monitor an SR Policy between the
local and the remote BFD peers. As defined in [RFC5880], the remote
BFD system does not process the payload of an Echo BFD.
A BSID can be used to specify the return path of an Echo BFD packet.
As introduced in [I-D.ietf-spring-bfd], the sender MAY use a Binding
SID (BSID) [RFC8402] that has been bound with the SR Policy that
ensures the return of a packet to that particular node and a BSID MAY
be associated with the SR Policy that is the reverse to the SR Policy
programmed onto the BFD Echo packet by the sender.
One way to implement this is through static configuration, e.g,
configure the BSID corresponding to the return path for each segment
list when enable BFD for an SR policy or an segment list.
This document introduces a method of dynamically configuring the
return path for an SR path, which can be used to specify the return
path in Echo BFD for SR, ICMPv6 for SRv6, etc.
2. SR Policy for Bidirectional Path
In order to specify the return path for an segment list when
delivering the SR Policy, and the tail node can return the packet
according to the specified return path, this document proposes
extensions of SR Policy. It allows the segment list to have its own
BSID.
When delivering SR policy, the BSID of the segment list and the
corresponding BSID of the return segment list can be carried
together.
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2.1. BGP Extensions for Advertising Segment List
Segment List sub-TLV is introduced in
[I-D.ietf-idr-segment-routing-te-policy] and it includes the elements
of the paths (i.e., segments).
This document introduces two optional sub-sub-tlvs of Segment List
sub-TLV, Binding SID Sub-TLV and Reverse Binding SID Sub-TLV.
The Binding SID sub-TLV has 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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (variable, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Binding SID Sub-TLV
where:
Type: TBD.
Length: specifies the length of the value field not including Type
and Length fields.
Binding SID: the BSID of the segment list.
The Reverse Binding SID sub-TLV has 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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Binding SID (variable, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Reverse Binding SID Sub-TLV
where:
Type: TBD
Length: specifies the length of the value field not including Type
and Length fields.
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Reverse Binding SID: the BSID of the reverse SR path. If it is
encapsulated in the packet, the Reverse Binding SID must the last
segment to be processed.
The extended SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Binding SID
Reverse Binding SID
Weight
Segment
Segment
...
Whether to carry RBSID in the packet can be configured according to
service requirements. For example, when echo BFD packets are
encapsulated, RBSID is carried in segment list, while packets of
other services do not carry RBSID by default. Thus BFD packets and
common service packets can share the same SR Policy.
2.2. Illustration
+-+ +-+ +-+ +-+
|A|------|B|------|C|------|D|
+-+ +-+ +-+ +-+
Figure 3: Reference Topology
The content of Segment List1 in SR Policy1 received by A is:
Segment List1
Reverse Binding SID D1
Segment B
Segment C
Segment D
The content of Segment List2 in SR Policy2 received by D is:
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Segment List2
Binding SID D1
Segment C
Segment B
Segment A
The SID-List of the BFD ECHO sent by A is < B, C, D, D1 >.
After the packet arrives at node D, D1 is Segment List2 BSID. BFD
packets are returned from node D according to segment list < C, B, A
>.
2.3. Difference from Path Segment
TBD
3. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-idr-segment-routing-te-policy] and
[I-D.ietf-spring-segment-routing-policy].
4. IANA Considerations
TBD
5. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-11 (work in progress), November 2020.
[I-D.ietf-spring-bfd]
Mirsky, G., Tantsura, J., Varlashkin, I., Chen, M., and J.
Wenying, "Bidirectional Forwarding Detection (BFD) in
Segment Routing Networks Using MPLS Dataplane", draft-
ietf-spring-bfd-00 (work in progress), September 2020.
[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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[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[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>.
Authors' Addresses
Liu Yao
ZTE Corporation
Nanjing
China
Email: liu.yao71@zte.com.cn
Peng Shaofu
ZTE Corporation
Nanjing
China
Email: peng.shaofu@zte.com.cn
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