Re: [Idr] F3-WG-Issue 1 - Topology (3/8 to 3/22)

[Kaliraj Vairavakkalai <[e-mail]>]

Hi Sue, Shunwan,

Following section in CT draft has the details, it uses the same topology:

https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-ct-01#section-20.3.1

We had replied to this issue (F3-WG-Issue-1-CT) in the following email:

https://mailarchive.ietf.org/arch/msg/idr/-SZOYCalQnvM4Wj9VmJN8eceiRw/

PS: Sue, can we start closing the github issues, that we have responded to?

thanks
kaliraj

From: Idr <[e-mail]> on behalf of Susan Hares <[e-mail]>
Date: Wednesday, March 8, 2023 at 1:10 PM
To: [e-mail] <[e-mail]>, Zhuangshunwan <[e-mail]>
Subject: [Idr] F3-WG-Issue 1 - Topology (3/8 to 3/22)
[External Email. Be cautious of content]

Greetings:

To resolve the Color Issues (CAR and CT drafts), the IDR WG needs to
agree on several topologies for these drafts to discuss.

The first discussion is provide a set of simple topologies
For incremental support.  CAR (draft-ietf-idr-car-00) provides
The following sample topology description for the case
when transit domains do not support Color.

Below is a topology that CAR provides in Appendix A.4.

Question 1: Does this topology common for CT where
   CT domains are connected by LU?

1a: If so, what methodology does CT use for signaling.

1b: If not, what is the equivalent topology for CT?

Shunwan Zhuang first brought this up.   He has
agreed to help discuss this topic.

Cheerily, Sue


=============
Topology:
A.4.  Transit network domains that do not support CAR

    In a brownfield deployment, color-aware paths between two PEs may
      need to go through a transit domain that does not support CAR.
      Example include an MPLS LDP network with IGP best-effort; or a
      BGP-LU based multi-domain network.  MPLS LDP network with best
      effort IGP can adopt above scheme.  Below is the example for BGP
      LU.

   *  Reference topology:

      E1 --- BR1 --- BR2 ......... BR3 ---- BR4 --- E2
          Ci           <----LU---->              Ci


      -  Network between BR2 and BR3 comprises of multiple BGP-LU hops
         (over IGP-LDP domains).

      -  BR1 and BR2 are directly connected; BR3 and BR4 are directly
         Connected


CAR signaling:
*- E1, BR1, BR4 and E2 are enabled for BGP CAR, with Ci colors

  *  BR1 and BR4 form an over-the-top peering (via RRs as needed) to
      exchange BGP CAR routes

   *  BR1 and BR4 also form direct BGP-LU sessions to BR2 and BR3
      respectively, to establish labeled paths between each other
      through the BGP-LU network

   *  BR1 recursively resolves the BGP CAR next-hop for CAR routes
      learnt from BR4 via the BGP-LU path to BR4

   *  BR1 signals the transport discontinuity to E1 via the AIGP TLV, so
      that E1 can prefer other paths if available

   *  BR4 does the same in the reverse direction

   *  Thus, the color-awareness of the routes and hence the paths in the
      data plane are maintained between E1 and E2, even if the intent is
      not available within the BGP-LU island



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