Re: Comments on raft-fz-6man-ipv6-alt-mark-01

Mark Smith <markzzzsmith@gmail.com> Tue, 05 November 2019 09:34 UTC

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From: Mark Smith <markzzzsmith@gmail.com>
Date: Tue, 5 Nov 2019 20:34:05 +1100
Message-ID: <CAO42Z2wBr-UoMG5xh=-7UGRyzYEaBEHOh+MmDynWJ3VN=6W=sg@mail.gmail.com>
Subject: Re: Comments on raft-fz-6man-ipv6-alt-mark-01
To: Ole Troan <otroan@employees.org>
Cc: Tianran Zhou <zhoutianran@huawei.com>, 6man WG <ipv6@ietf.org>
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On Tue, 5 Nov 2019, 20:05 Ole Troan, <otroan@employees.org>; wrote:

> Tianran,
>
> > Yes, I know 8200 considered and changed the way to process the HBH.
> > Do you mean the following words?
> > NOTE: While [RFC2460] required that all nodes must examine and
> > process the Hop-by-Hop Options header, it is now expected that nodes
> > along a packet's delivery path only examine and process the
> > Hop-by-Hop Options header if explicitly configured to do so.
> >
> > From this I am always confused. We can decide/configure whether to
> process the HBH. But we cannot decide whether it's processed in fast path
> or slow path. I think this is one issue raised by the reference
> > https://tools.ietf.org/html/draft-ietf-6man-hbh-header-handling-03
> > Do I miss some other words in 8200?
>
> Right, HBH processing by a router now has to be explicitly configured.
> E.g. if a router didn't support alt mark, it would be no purpose in even
> parsing the HBH header (unless other options also was configured and
> supported).
>
> You can of course not control how efficient that implementation implements
> your option...
>
> > In addition, we did test many asics and devices. They will direct packet
> to the slow path.
> > In addition, in real deployment, there are legacy devices that follow
> RFC2460.
> >
> > So our idea is to show alternative options for potential environment.
>
> Sure, and this was discussed a lot in the context of the other RFC.
>
> Hiding the per-hop options inside of destination options, would have
> pretty bad performance characteristics I would expect.
>
> For HBH a router needs to:
> if ipv6->nh == 0
>    walk HBH TLVs and process them
>
> For DestOpt a router would need to:
> walk EH chain looking for DestOpt:
>   walk DestOpt TLVs and make a guess which one is for in-flight versus
> destination
>


Yes, the *Destination* Options are for the device holding the packet's
*Destination* Address.



> Using HBH you use a mechanism engineered for it, using DestOpt you are in
> middlebox territory. And you will be much more likely to end up conflicting
> with host functions.
>
> Best regards,
> Ole
>
> PS: If you would do a EH performance testing project at the Singapore
> hackathon I would be all supportive.
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