Re: [Bier] WG adoption call for draft-chen-bier-frr-02

"Gengxuesong (Geng Xuesong)" <> Wed, 31 March 2021 02:04 UTC

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From: "Gengxuesong (Geng Xuesong)" <>
To: "" <>, "Jeffrey (Zhaohui) Zhang" <>
CC: BIER WG <>, BIER WG Chairs <>, "" <>, Huaimo Chen <>
Thread-Topic: [Bier] WG adoption call for draft-chen-bier-frr-02
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Date: Wed, 31 Mar 2021 02:04:17 +0000
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Subject: Re: [Bier] WG adoption call for draft-chen-bier-frr-02
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Hi Greg,

I agree that Jeffery has quite rich experience in BIER WG and participates in ML discussions actively. However, I still think the answer of “who should be the author of the document” depends mostly on “who raises the idea and brings it to IETF”. This is a basic respect for the originality of the author.
Of course, if anyone is interested in this topic, he/she could contribute and co-author the document, when the existing authors would like to.


From: BIER [] On Behalf Of Greg Shepherd
Sent: Wednesday, March 31, 2021 12:11 AM
To: Jeffrey (Zhaohui) Zhang <>
Cc: BIER WG <>rg>; BIER WG Chairs <>rg>; <>cn>; Huaimo Chen <>
Subject: Re: [Bier] WG adoption call for draft-chen-bier-frr-02

I agree with Jeffrey. The two drafts should be merged into a new draft, which we will then call to adopt. I suggest that the authors of each of the two docs:

..contribute two authors to the merged doc effort, and have Jeffrey hold the pen as editor/author.

All agreed?


On Mon, Mar 29, 2021 at 7:26 PM Jeffrey (Zhaohui) Zhang <<>> wrote:
Shouldn’t it be the other way around – expand/merge first and then adopt?

In fact, the essence of draft-chen is the multiple per-nbr FRR BIFTs, which I don’t think should be included in the merged draft at all, for the following problems:

  1.  Scaling – we need one extra BIFT for each <neighbor, BIFT>. This not only means extra memory, but also additional processing overhead including downloading the tables to the forwarding plane.
  2.  If two neighbors fail simultaneously yet both can be protected by a 3rd neighbor, per-nbr FRR BIFTs can only give protection for one of the first two neighbors. This is not an unusual situation – you could have two neighbors reached by the same link or the same line card, and the link/card fails.
  3.  Exactly when to switch back from a per-nbr FRR BIFT to the regular BIFT?

The draft says the following about #3:

   In general, when the routing protocol has re-converged on the new
   topology taking into account the failure of X, the BIRT is re-
   computed using the updated LSDB and the BIFT is re-derived from the
   BIRT.  Once the BIFT is installed ready for activation, it is
   activated to forward packets with BIER headers and the FRR-BIFT for X
   is de-activated.

Does that mean for each computation, you need to know and mark which failed neighbor that it takes care of, so that when the BIFT is sent down to forwarding plane you can decide if currently used FRR-BIFT can be switched back to the main BIFT?

Also consider the following:

  1.  At moment T you switch to FRR BIFT for nbr X
  2.  At moment T+1ms a new BIFT is calculated, which takes care of a remote failure but not nbr X (nbr X is still considered up in this calculation) – would you switch FRR BIFT to the newly calculated main BIFT? If you don’t, the remote failure could lead to packet losses until the new main BIFT is used. If you do, you only get FRR protection for nbr X for 1ms.


From: BIER <<>> On Behalf Of Huaimo Chen
Sent: Thursday, March 25, 2021 5:06 PM
To: Tony Przygienda <<>>;<> <<>>
Cc: BIER WG <<>>; BIER WG Chairs <<>>
Subject: Re: [Bier] WG adoption call for draft-chen-bier-frr-02

[External Email. Be cautious of content]

Hi Everyone,

    Michael, Steffan, Huaimo and Mike met to discuss the merge and we are in agreement that if draft-chen-bier-frr is adopted we will expand it to include a framework along with the tunnel and LFA based solutions.

Best Regards,
From: BIER <<>> on behalf of Tony Przygienda <<>>
Sent: Tuesday, March 16, 2021 6:08 AM
To: zhang.zheng <<>>
Cc: BIER WG <<>>; BIER WG Chairs <<>>
Subject: Re: [Bier] WG adoption call for draft-chen-bier-frr-02


I think it's a good addition within the architecture for the case IGP is not used for signalling, e.g. when controller or static programming.

The draft must however explain in what scenarios it is used and quote the according IGP drafts to guarantee loop-free behavior (well, BIER will tie-break loops but we'll have 1x microloop & possibly not deliver payload if BIER FRR is not properly computed/intsalled). With that the draft should also pay attention to how the function is deployed/updated network-wide if IGP is not present


-- tony

On Tue, Mar 16, 2021 at 7:41 AM <<>> wrote:

A 2-week WG adoption call begins for the following draft:<*3A*2F**2Fdoc*2Fdraft-chen-bier-frr*2F&data=04*7C01*7Chuaimo.chen**7C79ac63710b47427a558d08d8e8638df2*7C0fee8ff2a3b240189c753a1d5591fedc*7C1*7C1*7C637514861570555970*7CUnknown*7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0*3D*7C1000&sdata=DiHvux0ZUYEJru10lVQ4mXvpYx3l8ujGInm7uEjjxTw*3D&reserved=0__;JSUlJSUlJSUlJSUlJSUlJSUlJQ!!NEt6yMaO-gk!TtAnkZJhg9BEJjANzO6CusX7i7eQqvTJHdhaH0qrrPdtcykRPrUybhZeavPA3X4F$>

Please indicate your support or objection by March 30th, 2021.

Authors, please respond to the list indicating whether you are aware of any IPR that applies to this draft.


Sandy (As WG secretary, on behalf of Greg/Tony)

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