[Bier] Questions about draft-ietf-bier-te-ospfv3

"Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net> Tue, 05 July 2022 13:33 UTC

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From: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>
To: "'bier@ietf.org'" <bier@ietf.org>, "draft-ietf-bier-te-ospfv3@ietf.org" <draft-ietf-bier-te-ospfv3@ietf.org>
Thread-Topic: Questions about draft-ietf-bier-te-ospfv3
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Subject: [Bier] Questions about draft-ietf-bier-te-ospfv3
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Hi Huaimo,

I am catching up some BIER reading and have some questions here. I am sorry if they have been raised and answered before - please just give me a link to the archive in that case.

I noticed that the WG version is not linked to draft-chen version.

If I understand it correctly, BIER-TE BIFTs are not calculated but programmed based on planning. On each BFR, a bit-position is assigned to a link that is used for BIER-TE forwarding purposes, or to a "tunnel" that leads to a remote BFR (i.e., routed adjacency). That information is only useful locally (in the BIFT) and on the controller that determines the bitstring to use. Other BFRs won't use that.

Therefore, flooding that information in IGP does not seem to be useful (unless each BFIR determines on its own what BitString to use)? For the same reason, signaling MT/BAR/IPA information does not seem to be useful either. While https://datatracker.ietf.org/doc/html/draft-ietf-bier-te-arch-13#section-3.2.1 does not preclude distributed model (e.g., each BFIR determines on its own what BitString to use to identify a tree), it does not seem to be an expected scenario; if this document intends to address that it should be made clear.

It seems to me that the information should be signaled from a controller/orchestrator directly to targeted individual BFRs using other Netconf/PCEP/BGP.

Besides that, the signaling in the draft does not cover "routed adjacency". For the direct p2p links, it assumes different bits are assigned for the two BFRs connected by the link. However, that is different from the following in BIER-TE arch spec:

5.1.1.  P2P Links

   On a P2P link that connects two BFRs, the same bit position can be
   used on both BFRs for the adjacency to the neighboring BFR.  A P2P
   link requires therefore only one bit position.

It is also not clear if BIFT-ID ranges need to be signaled (so that when BFR1 sends traffic to BFR2 according to the programmed BIFT, it knows what BIER label to use). I assume the BIFT-IDs (to be used to reach a neighbor) can also be signaled from the controller as part of local BIFT entries?

Thanks.

Jeffrey


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