Network Working Group Z. Li
Internet-Draft T. Sun
Intended status: Informational China Mobile
Expires: January 9, 2022 W. Cheng
J. Wang
Centec
July 8, 2021
S-BFD over SRv6
draft-li-sbfd-over-srv6-00
Abstract
Bidirectional Forwarding Detection (BFD) can be used to monitor paths
between node. Seamless BFD (S-BFD) provides a simplified mechanism
which is suitable for monitoring of paths that are setup dynamically
and on a large scale network. This draft describes a method to
simplify the implementation of S-BFD over SRv6 by using SRH.flag to
instruct the S-BFD peer node to do reverse operation of SRv6 SID
list.
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 .
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This Internet-Draft will expire on January 9, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motiviation for Proposing S-BFD over SRv6 . . . . . . . . . . 2
3. The benefits of S-BFD over SRv6 . . . . . . . . . . . . . . . 4
4. Future Considerations and Enhancements of S-BFD over SRv6 . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
With the increasing adoption of segment routing (SR) technology, ISPs
have upgraded their networks seamlessly from MPLS to SR MPLS, and
their next goal might be the overall upgrading of the IPv6 underlay
network forwarding plane.
We hope to implement BFD over SRv6 while retaining the bidirectional
detection capabilities of traditional BFD, rather than using
asymmetrical path detection only. Another problem relates to the
bidirectional detection mechanism in BFD over SRv6, Using SR Policy
or using TLV to carry the return path brings extra load to the
message parsing depth on existing SRv6 device.
In order to accelerate applying BFD in SRv6 networks, this paper
proposed a S-BFD over SRv6 implementation solution.
2. Motiviation for Proposing S-BFD over SRv6
As shown in the figure below, the BFD initiator is A and the peer
node is D, while bfd packets forwarding from A to D via the path:
A->B->C->D, and return via the path: D->C->B->A.
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+-----B-------C-----+
/ \
A-----------E-----------D
\ /
+-----F-------G-----+
Forward Paths: A-B-C-D
Return Paths: D-C-B-A
Traditional BFD in SRv6 Data Plane
SRv6 SID operations on the initial node A: The SRv6 SID list {A, B,
C, D} is pushed into Node A.
SRv6 SID operations on the terminal node D: The SRv6 SID list {A, B,
C, D} is swapped in Node D, and the updated SRv6 SID list is : {D, C,
B, A}, and the Last Entry, Segment Left, and other fields are
updated.Return Path: D->C->B->A.
As shown in the figure below, the length of the flags field in the
SRH header is 8-bit. This draft uses the left third bit
(0|0|R|0|0|0|0|0) to represent the reverse operation of the SRv6 SID
list.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hdr=144 | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128-bit IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128-bit IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 SPAN Header |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Origin Packet |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The reverse operations for S-BFD of SRv6 Flag
BFD peer node D check if SRH.Flags[5] == 1, it means that this device
requires the reverse operation of the SRv6 SID list.
3. The benefits of S-BFD over SRv6
This solution does not need to use the SRv6 Policy to add length of
the SID list or to carry the SID list of the return path by TLV. It
only needs to support reverse SRv6 SID in the reflector node to solve
the issue of S-BFD over SRv6 described in the previous.
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4. Future Considerations and Enhancements of S-BFD over SRv6
In future versions of this paper, we will also consider the
compatibility of using compressed IDs in SRv6, such as seamlessly
merging S-BFD over G-SRv6. Furthermore, there will be no effect on
intermediate nodes within the SRv6 network and it only requires S-BFD
reflector support the SID reverse operation.
5. Security Considerations
TBD.
6. IANA Considerations
TBD.
Authors' Addresses
Zhiqiang Li
China Mobile
Beijing 100053
China
Email: lizhiqiangyjy@chinamobile.com
Tao Sun
China Mobile
Beijing 100053
China
Email: suntao@chinamobile.com
Wei Cheng
Centec
Suzhou 215000
China
Email: chengw@centecnetworks.com
Junjie Wang
Centec
Suzhou 21500
China
Email: wangjj@centecnetworks.com
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