[spring] 答复: Beyond SRv6.

[Lizhenbin <[e-mail]>]

Hi Folks,

I have explained opinions in the session meeting of IETF104. Here I would like to summarize it agian:

1. Problem Statement

There are three three major concerns about SRH:

1) Path MTU: In theory it may be an issue. But as the develoment of the link layer technology, the network administrators always configure the MTU as the size of Jambo Frame (That is up to 9000B) to prevent unnecessary problems. Even without SRv6 they already do like this way. So the MTU is not a big issue in the current network.

2) Payload efficiency: According to the statistics information from CAIDA and other sources, the average packet size is above 512B. When introduce 3-5 SRv6 segment ,the decreas of payload efficiency is under control. We do not think in a short time we will need up to 10 or 10+ segments which is only theoretic or to extensively use SRv6 segment.

3) Forwarding efficiency: Huawei product already supports up to 10 layers of segments for SRv6 SRH. I believe more hardware can support enough segments in a short time which is faster than the standardization process for the new encapsulation.



Besides above fact in the existing network, we can also take SR-MPLS as the example. Five years ago, people also worried about such issues. After 5 years we can learn what happens which is much less serious than what was concerned.



2. Solutions

According to the analysis of the problem statement, for the possible solutions I have following suggesions:

1) The price should be low. Compressing is just optimizaiton and will not add new services. We need not introduce a new set of control plane and forwarding plane extensions which will take a long time for standardization. That is the reason why we proposed the C-SRH (https://tools.ietf.org/html/draft-li-spring-compressed-srv6-np-00 ). We think its price is low enough since it will not change the existing control plane of SRv6. Even so we still think Binding SID should be the first choice. It is simplest and more mature after the verication in SR-MPLS.

2) Avoid the repeated work: After a long work the solutions based on SRH is already mature. Firstly we should avoid a new set of protocol extensions. Secondly if there is concern on the size of IPv6 dataplane which may be caused by strict TE or SFC, it is uncessary to repeat work on VPN, OAM, etc.





Thinking about the comming IGP/BGP/PCEP/BESS/6MAN/etc. work on the topic, in order to avoid the possible waste on the standarization effort and we already learned much from the discussion on the problem statement and requirement, we could have a draft to consolidate them as a base firstly for further discussion, then begin to do possible protocol work.







Best Regards,

Zhenbin (Robin)

























________________________________
发件人: spring [[e-mail]] 代表 Rob Shakir [robjs=[e-mail]]
发送时间: 2019年8月5日 5:03
收件人: SPRING WG List
主题: [spring] Beyond SRv6.


Hi SPRING WG,


Over the last 5+ years, the IETF has developed Source Packet Routing in NetworkinG (SPRING) aka Segment Routing for both the MPLS (SR-MPLS) and IPv6 (SRv6) data planes. SR-MPLS may also be transported over IP in UDP or GRE.


These encapsulations are past WG last call (in IESG or RFC Editor).


During the SPRING WG meeting at IETF 105, two presentations were related to the reduction of the size of the SID for IPv6 dataplane:

  *   SRv6+ / CRH -- https://tools.ietf.org/html/draft-bonica-spring-srv6-plus-04

  *   uSID -- https://tools.ietf.org/html/draft-filsfils-spring-net-pgm-extension-srv6-usid-01


During the IETF week, two additional drafts have been proposed:

  *   https://tools.ietf.org/html/draft-li-spring-compressed-srv6-np-00

  *   https://tools.ietf.org/html/draft-mirsky-6man-unified-id-sr-03


As we expressed during the meeting, it is important for the WG to understand what the aims of additional encapsulations are. Thus, we think it is important that the WG should first get to a common understanding on the requirements for a new IPv6 data plane with a smaller SID - both from the perspective of operators that are looking to deploy these technologies, and from that of the software/hardware implementation.


Therefore, we would like to solicit network operators interested in SR over the IPv6 data plane to briefly introduce their:

  *   use case (e.g. Fast Reroute, explicit routing/TE)

  *   forwarding performance and scaling requirements

     *   e.g., (number of nodes, network diameter, number of SID required in max and average). For the latter, if possible using both SRv6 128-bit SIDs and shorter (e.g. 32-bit) SIDs as the number would typically be different (*).

  *   if the existing SRv6 approach is not deployable in their circumstances, details of the requirement of a different solution is required and whether this solution is needed for the short term only or for the long term.


As well as deployment limitations, we would like the SPRING community to briefly describe the platform limitations that they are seeing which limit the deployment of SRv6  In particular limitations related to the number of SIDs which can be pushed and forwarded and how much the use of shorter SIDs would improve the deployments .


For both of these sets of feedback if possible, please post this to the SPRING WG. If the information cannot be shared publicly, please send it directly to the chairs & AD (Martin).


This call for information will run for four weeks, up to 2019/09/03. As a reminder, you can reach the SPRING chairs via [e-mail]<mailto:[e-mail]> and ADs via [e-mail]<mailto:[e-mail]>.


Thank you,

-- Rob & Bruno


(*) As expressed on the mailing list, a 128 bit SID can encode two instructions a node SID and an adjacency SID hence less SID may be required.