Re: [Idr] I-D Action: draft-ietf-idr-bgp-fwd-rr-02.txt

[Kaliraj Vairavakkalai <[e-mail]>]

Hi Robert, please see inline. KV>

Thanks
Kaliraj



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From: Robert Raszuk <[e-mail]>
Date: Sunday, March 17, 2024 at 11:28 PM
To: Kaliraj Vairavakkalai <[e-mail]>
Cc: idr@ietf. org <[e-mail]>
Subject: Fwd: I-D Action: draft-ietf-idr-bgp-fwd-rr-02.txt
[External Email. Be cautious of content]

Hi Kaliraj,

Thx for posting the new version.

I have one observation or clarification to be made in respect to text you added in section 4.1:

> However this approach does not allow the ABR-ABR tunnels to be
> used as backup path, in the event where an ABR looses all tunnels
> to upstream ASBR.

So you are talking about the delta time it takes for ABR which looses all tunnels to upstream ASBRs to send BGP withdraws for those learned infrastructure routes - correct ?

KV> Yes. Those withdrawals need to anyway happen, and reach both the ingress PEs and adjoining/redundant ABR.
KV> So that they can do BGP PIC repair based on that event.
KV> Here I am saying that such BGP PIC repair can happen only at ingress PE
KV> (which may be multiple BGP hops away), and not at the adjoining ABR.

So we are talking 10s of milliseconds here from the moment all such paths are invalidated (which  -the detection and invalidation is needed in any scenario).

KV> The BGP update propagation can take longer, based on load on the BGP propagation path. But BGP PIC itself can’t always
KV> guarantee 10s of ms restoration. It only guarantees restoring the traffic without depending on service-prefix scale
KV> once the unreachability is detected (in this case: BGP withdrawal is received).

As you have established each ABR will set next hop self and advertise routes to local PEs (directly or via yet one more pair of RRs (RR26 here)). So each PE will already have backup paths all what you are observing here is the time before PEs invalidate paths advertised by ASBR which looses upstream tunnels.

KV> Agreed.

So if such failure models are really likely to happen (in spite of redundant ABR connectivity in each area)  I would rather focus on fast removal of broken paths from the network with one next hop invalidation (single BGP or IGP message, single RIB to FIB switchover on PEs) etc ...

KV> As explained above, that would also happen. But it may take longer than if the repair happened at the ABR, which is closer to the failure event.
KV> Just a tradeoff to be aware of. Thx.

Thx,
Robert

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Date: Sun, Mar 17, 2024 at 6:42 AM
Subject: I-D Action: draft-ietf-idr-bgp-fwd-rr-02.txt
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Cc: <[e-mail]<mailto:[e-mail]>>


Internet-Draft draft-ietf-idr-bgp-fwd-rr-02.txt is now available. It is a work
item of the Inter-Domain Routing (IDR) WG of the IETF.

   Title:   BGP Route Reflector with Next Hop Self
   Authors: Kaliraj Vairavakkalai
            Natrajan Venkataraman
   Name:    draft-ietf-idr-bgp-fwd-rr-02.txt
   Pages:   9
   Dates:   2024-03-16

Abstract:

   The procedures in BGP Route Reflection (RR) spec RFC4456 primarily
   deal with scenarios where the RR is reflecting BGP routes with next
   hop unchanged.  In some deployments like Inter-AS Option C
   (Section 10, RFC4364), the ABRs may perform RR functionality with
   nexthop set to self.  If adequate precautions are not taken, the
   RFC4456 procedures can result in traffic forwarding loop in such
   deployments.

   This document illustrates one such looping scenario, and specifies
   approaches to minimize possiblity of traffic forwarding loop in such
   deployments.  An example with Inter-AS Option C (Section 10, RFC4364)
   deployment is used, where RR with next hop self is used at redundant
   ABRs when they re-advertise BGP transport family routes between
   multiple IGP domains.

The IETF datatracker status page for this Internet-Draft is:
https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-fwd-rr/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-idr-bgp-fwd-rr/__;!!NEt6yMaO-gk!Hv7GNYr6n89i4QRD_aXV0QhV0N_J6YWRal9RjghMoB6DdmitfkQrjPi8YKCDbwPDc6YiEq2NYiMTgzkj$>

There is also an HTMLized version available at:
https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-fwd-rr-02<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-fwd-rr-02__;!!NEt6yMaO-gk!Hv7GNYr6n89i4QRD_aXV0QhV0N_J6YWRal9RjghMoB6DdmitfkQrjPi8YKCDbwPDc6YiEq2NYmrSzwvH$>

A diff from the previous version is available at:
https://author-tools.ietf.org/iddiff?url2=draft-ietf-idr-bgp-fwd-rr-02<https://urldefense.com/v3/__https:/author-tools.ietf.org/iddiff?url2=draft-ietf-idr-bgp-fwd-rr-02__;!!NEt6yMaO-gk!Hv7GNYr6n89i4QRD_aXV0QhV0N_J6YWRal9RjghMoB6DdmitfkQrjPi8YKCDbwPDc6YiEq2NYmTSTQwU$>

Internet-Drafts are also available by rsync at:
rsync.ietf.org::internet-drafts


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