Re: [Bier] WGLC: draft-ietf-bier-php

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Hi Loa,

Please see zzh> below.

-----Original Message-----
From: BIER <[e-mail]> On Behalf Of Loa Andersson
Sent: Saturday, August 22, 2020 1:57 AM
To: Gyan Mishra <[e-mail]>; Mankamana Mishra (mankamis) <mankamis=[e-mail]>
Cc: IJsbrand Wijnands (iwijnand) <iwijnand=[e-mail]>; Greg Shepherd <[e-mail]>; [e-mail]
Subject: Re: [Bier] WGLC: draft-ietf-bier-php

[External Email. Be cautious of content]


Working Group,

I've had time to read the draft a bit more in detail.

I'm convinced that this will work, and support progressing the draft.

I still think there are some minor description details that could be improved.

The draft says:

    One way to solve this problem is to use Penultimate Hop Popping (PHP)
    so that the upstream BFR can pop the BIER header and send the payload
    "natively" (note that the upstream BFR can be connected directly or
    indirectly via any type of tunnel to the PE).  This is similar to
    Multi-Protocol Label Switching (MPLS) PHP though it is the BIER
    header that is popped.

This indicate that this is a "per node" decision, while in MPLS it is a per LSP decision.

Zzh> It’s a per node decision for all traffic to a particular “BFER” who does not really support BIER forwarding. PHP is not used when the BFERs do support BIER.

I would think that it is possible for one node to be the penultimate node for some traffic but not for other traffic, even though the traffic is sent to the same node, which can be both ultimate node, pen-ultimate node or transit node.

      +-------+              +-------+          +-------+
      |       |              |       |          |       |
 -a,b-+   A   +-----a',b-----+   B   +----a'----+  CPE1 |
      |       |              |       |          |       |
      +-------+              +---+---+          +-------+
                                 |
                                 b'
                                 |
                             +---+---+          +-------+
                             |       |          |       |
                             +   C   +----b'----+  CPE2 |
                             |       |          |       |
                             +---+---+          +-------+


Two streams comes in to A from the left (a and b).

A is the penultimate node for traffic to to CPE1 (a) so the BIER header is popped.

A is not the  penultimate node for traffic to to CPE2 (b) so the BIER header is not popped.

Zzh> So the context is that B does support BIER. In that case, A won’t do PHP for B at all.

Both a' and b is sent to B.

B forward a' natively to CPE1.

B is the penultimate node for traffic to to CPE2 (b) so the BIER header is popped.

b' is forwarded to C and onto CPE2

Works just fine.

Question: If the PHP is a "per node decision" how is A stopped from doing PHP for b?

Zzh> Please see above :-)
Zzh> Thanks.
Zzh> Jeffrey

/Loa



On 22/08/2020 05:20, Gyan Mishra wrote:
>
> I support advancing this critical draft forward.  I agree that the PHP
> feature traditionally used with MPLS and has been adopted by SR and
> now by BIER for similar reasons of being able to pop the BIER header
> similar to what is done with SR PHP concept and now extensible with
> BIER for Non-BRF capable PE's.
>
> BIER IPv6 is still being developed, however I think maybe BIERin6
> could take advantage of  PHP by popping the encapsulated L2 1/2 BIER
> shim for "Non-BFR" capable PE.  I think for BIERv6 as the BIER header
> is encoded in DOH it may be difficult to support PHP.
>
> Thanks
>
> Gyan
>
> On Wed, Aug 19, 2020 at 2:01 PM Mankamana Mishra (mankamis)
> <mankamis=[e-mail]
> <mailto:[e-mail]>> wrote:
>
>     Support moving this document forward. ____
>
>     __ __
>
>     *From: *BIER <[e-mail] <mailto:[e-mail]<mailto:[e-mail]%20<mailto:[e-mail]>>>
>     on behalf of "IJsbrand Wijnands (iwijnand)"
>     <iwijnand=[e-mail]
>     <mailto:[e-mail]>>
>     *Date: *Monday, August 17, 2020 at 11:56 AM
>     *To: *Greg Shepherd <[e-mail] <mailto:[e-mail]<mailto:[e-mail]%20<mailto:[e-mail]>>>
>     *Cc: *"[e-mail] <mailto:[e-mail]><mailto:[e-mail]%20<mailto:[e-mail]>>" <[e-mail]
>     <mailto:[e-mail]>>
>     *Subject: *Re: [Bier] WGLC: draft-ietf-bier-php____
>
>     __ __
>
>     In support moving this draft forward, ____
>
>     __ __
>
>     Thx,____
>
>     __ __
>
>     Ice.____
>
>     Sent from my iPhone____
>
>
>
>     ____
>
>         On 13 Aug 2020, at 05:31, Greg Shepherd <[e-mail]
>         <mailto:[e-mail]>> wrote:____
>
>
>         Please read and respond to this thread. We had a WGLC for this
>         draft previously, but had no response. Let’s do better. ____
>
>         __ __
>
>
> https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-iet
> f-bier-php/______;!!NEt6yMaO-gk!Ws4otxDsuVKTsaEjyRKVYz-hcmmmGgDiE7Cnpq
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>
>         __ __
>
>         Start of short LC timer. Respond by Aug 19..____
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>
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--

Loa Andersson                        email: [e-mail]<mailto:[e-mail]>
Senior MPLS Expert                          [e-mail]<mailto:[e-mail]>
Bronze Dragon Consulting             phone: [phone]

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