Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>

Xiejingrong <> Tue, 16 July 2019 09:29 UTC

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From: Xiejingrong <>
To: Tony Przygienda <>, "Jeffrey (Zhaohui) Zhang" <>
CC: Senthil Dhanaraj <>, "Jeffrey (Zhaohui) Zhang" <>, BIER WG <>, "" <>, Antoni Przygienda <>
Thread-Topic: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>
Date: Tue, 16 Jul 2019 09:28:55 +0000
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Subject: Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>
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Hi Tony, Jeffrey:
Let’s f2f in BIER session at Montreal.
Here is a page I think useful to understand the difference between Layer-4 solution(left) and Layer-3 solution(right).
That’s why I think use of a preceding End.BIER is most efficient (for BIER forwarding), least impact (to exist functions), and most extensible for future functions.

The least impact:  Switch-case by preceding FIB lookup doesn’t impact other cases.
The most efficient:  Do not need walking through EH ---- only check the first EH.
The most extensible to support features in the future:   Combine with Routing Header(e.g., SRH), Fragmentation, AH or ESP.  Support Multiple BIER TLVs in a single Destination Options header. etc.


From: Tony Przygienda []
Sent: Monday, July 15, 2019 11:58 PM
To: Xiejingrong <>
Cc: Senthil Dhanaraj <>om>; Jeffrey (Zhaohui) Zhang <>rg>; BIER WG <>rg>;; Antoni Przygienda <>
Subject: Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>

On Mon, Jul 15, 2019 at 12:39 AM Xiejingrong <<>> wrote:
Please see my comments below:

From: Tony Przygienda [<>]
Sent: Monday, July 15, 2019 3:04 PM
To: Senthil Dhanaraj <<>>
Cc: Jeffrey (Zhaohui) Zhang <<>>; Xiejingrong <<>>; BIER WG <<>>;<>; Antoni Przygienda <<>>
Subject: Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>

if your router can do BIER fast path IPv6 is not an interesting option no matter which draft.
[XJR] That’s not true. The interest in BIER-IPv6-fast-path is strong.  There is no problem of “interest” or “requirement”. The problem is the lack of convinced  “technology” or “solution”.

enlighten me where you saw that except being personally convinced it's cool ... And what is the specific reason customer would want that complexity/cost of v6 option processing silicon compared to ether/mpls encaps.

one would either carry native ether or MPLS rather than trying to build IPv6 fast path with header options @ arbitrary place,
probably misaligning bitmasks and ultimately forcing 4K buffers on v6 option processing in silicon which may be fun but it is expensive, complex fun.
[XJR] The proposals are not as good as expected,  or could not do it in a simple and inexpensive way! I guess this is the point.

yupp. MPLS/Ether will be as inexpensive as it can be and shares same processing block.

[XJR] Well I think, using a preceding BIER-Specific IPv6 Address in IPv6 DA can solve the problem perfectly.
[XJR] This is the way SRv6/SRH do, which first introduces the fast-path processing of extension header, without recognition the pattern of the EHs and the TLVs, but simply ‘process the desired packet, and drop the undesired packet’!

BIER is neither SRv6 nor SRH so your point here is?

BIER is a L2.5 hop-by-hop multicast switching technology that should be tunneled otherwise. v6 enaps (where we really abuse v6 as L1 transport) is only justified if ether/mpls cannot be implemented but chips can do very simple v6 processing and there is not high throughput requirement (albeit one could build bierin6 fast-path in silicon obviously). Obviously bierin6 gives you the nice trick to tunnel it to a v6 destination without establishing a real tunnel but it's really just a by-product and not its main goal

--- tony