Re: [Idr] A naive question about draft-lin-idr-sr-epe-over-l2bundle

[linchangwang <[e-mail]>]

Hi Sasha,

Thank you for your question. The specific response is as follows:

By using BGP EPE to support label distribution based on member ports, the network controller can have fine-grained control over the egress traffic.
Please refer to this presentation material on IDR for more details:
 https://datatracker.ietf.org/meeting/118/materials/slides-118-idr-sessa-1-1segment-routing-bgp-egress-peer-engineering-over-layer-2-bundle
https://datatracker.ietf.org/doc/html/draft-lin-idr-sr-epe-over-l2bundle-03

For example, when a BGP neighbor is established through an aggregate interface with three member ports, BGP can assign labels based on peer_adj and peer_adj_member as follows:


  *   PeerAdj SID TLV (Label-1010)
o    L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 1)
*L2 Bundle Member PeerAdj SID TLV (Label-1011)
*Min/Max Unidirectional Link Delay TLV (Delay of member link 1)
o    L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 2)
   *L2 Bundle Member PeerAdj SID TLV (Label-1012)
   *Min/Max Unidirectional Link Delay TLV (Delay of member link 2)
o    L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 3)
*L2 Bundle Member PeerAdj SID TLV (Label-1013)
  *Min/Max Unidirectional Link Delay TLV (Delay of member link 3)
BGP needs to respond to member interface change events on the aggregate interface.
For example, if member port 1 fails, when advertising BGP-LS EPE information, only member ports 2 and 3 will be advertised as follows:


  *   PeerAdj SID TLV (Label-1010)
o    L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 2)
  L2 Bundle Member PeerAdj SID TLV (Label-1012)
  Min/Max Unidirectional Link Delay TLV (Delay of member link 2)
o    L2 Bundle Member Attribute TLV (Link Local Identifier describing the member link 3)
* L2 Bundle Member PeerAdj SID TLV (Label-1013)
  *Min/Max Unidirectional Link Delay TLV (Delay of member link 3)
      Then, the controller receives network changes through BGP-LS and performs path computation again.


Thanks,
Changwang

From: Alexander Vainshtein [mailto:[e-mail]]
Sent: Tuesday, November 07, 2023 8:27 PM
To: linchangwang (RD); [e-mail]; [e-mail]; chenmengxiao (RD)
Subject: FW: A naive question about draft-lin-idr-sr-epe-over-l2bundle

Hi,
Forwarding directly to you – the IETF mailer cannot expand the [e-mail]<mailto:[e-mail]> address.


Regards,
Sasha

From: Alexander Vainshtein
Sent: Tuesday, November 7, 2023 2:19 PM
To: [e-mail]
Cc: [e-mail]; Nitsan Dolev <[e-mail]>
Subject: A naive question about draft-lin-idr-sr-epe-over-l2bundle

Hi all,
Could the authors of the draft in question<https://datatracker.ietf.org/doc/html/draft-lin-idr-sr-epe-over-l2bundle-03> please clarify what is supposed to happen with the advertised bundle member-specific EPE SID if the link to which it refers fails?

Such failure would not necessarily  result in failure of the BGP neighborship.

Regards, and lots of thanks in advance,
Sasha



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