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SRv6 Policy HLD #1707

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SRv6 Policy HLD #1707

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eddieruan-alibaba
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linux-foundation-easycla bot commented Jun 4, 2024 •
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https://github.com/eddieruan-alibaba/SONiC/blob/eruan-srv6p/doc/srv6/srv6_policy.md

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kperumalbfn
kperumalbfn reviewed Jun 21, 2024
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doc/srv6/srv6_policy.md
6) "fd00:201:201:fff1:11::,fd00:202:202:fff2:22::"
7) "seg_src"
8) "2064:100::1f,2064:100::1f"
```
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Does fpmsyncd create NHGroup table based on PIC_CONTEXT_TABLE?

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PIC_CONTEXT_TABLE is for VPN SID, not for TE/ Policy, which is discussed in https://github.com/eddieruan-alibaba/SONiC/blob/eruan-pic/doc/pic/bgp_pic_edge.md#high-level-design

doc/srv6/srv6_policy.md
In this case, the default state is DOWN. bfd notification would be used to update cpaths' state.

### Policy with endpoint
bfd packet would be constructed with SRv6 header which would go via both specified cpath and engpoint. The protection path would be via specified SID notes and the end point node. This protection would not cover link if the SID list is not hop by hop.
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Does it make use of h/w offloaded BFD?

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Both software and hw offload, depending on BFD timer and scale.

doc/srv6/srv6_policy.md

### Policy without endpoint, a.ka. Color Only Policy

bfd packet would be constructed with SRv6 header which would go via the specified cpath.
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Hardware offloaded BFD with SRV6 header will require SAI BFD object changes.

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Yes，the SAI changes has been merged.
opencomputeproject/SAI#1759

@BorisH2018
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Hi,
Eddie , here are few more comments additionally to those which I made on Thursday's call.

  1. Binding SID (BSID) is not ,mentioned at all in the HLD. RFC 9256 (SR Policy Architecture) 6.1 says: "Each candidate path MAY be defined with a BSID." So in forwarding plane BSID can be mapped into an another Segment List (NHG). IMO, this functionality is quite important. Will it be included in some later version?

  2. FRR SRv6 Policy Configuration section

  1. Add "ipv6-address" as segment type for segment list for SRv6. Currently, FRR CLI only has "mpls" and "nai" as the segment type.

May be would be better to say explicitly that Type B segment type (item 4. RFC 9256) is supported in FRR)?

  1. HLD mentions BFD, why can't we also use S-BFD?

  2. I also have not seen in configuration the discriminator of CP (2.5, RFC 9256). Is it in roadmap?

  3. Also to align with RFC 9256, would be better to mention that HLD currently focuses on explicit CPs.

  4. Forwarding information NHG's schema
    "Zebra maintains a SRv6 Policy NHG in two levels. The first level is for ECMP over multiple polices, and the second level is for ECMP over multiple candidate paths." -> It is not clear, why do we need ECMP over multiple policies? Do you mean a composite CP (2.2 RFC 9256) ? It is quite rare implementation case and would be good to clarify it. Also according to the configuration a 1st level of an ECMP is an ECMP over SLs.

Thank you.

SY,
Boris

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@eddieruan-alibaba @BorisH2018 @kperumalbfn @shuaishang