Re: [nvo3-dt-encap] [nvo3] Encap draft published by design team

Joe Touch <touch@isi.edu> Thu, 09 February 2017 21:11 UTC

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To: Tom Herbert <tom@herbertland.com>
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From: Joe Touch <touch@isi.edu>
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Date: Thu, 9 Feb 2017 13:10:33 -0800
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Subject: Re: [nvo3-dt-encap] [nvo3] Encap draft published by design team
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On 2/9/2017 12:05 PM, Tom Herbert wrote:
>> Otherwise, the only way to know where the Nth TLV field starts is to
>> parse through the N-1th, which - recursively - reduces to requiring
>> iterative processing.
>>
> Yes, and iterative processing of an open ended list of TLVs is still
> hard to do in hardware _and_ software and in fact is an obvious DOS
> vector. Last I checked OpenFlow, P4, and eBPF don't fully implement
> loops that are needed to process an arbitrary list of TLVs (they
> resolved this through some hackery and artificial constraints). The
> unlimited flexibility of TLVs does not come without a cost...
Wouldn't the obvious solution be to let the entire encapsulation
protocol be negotiated by the endpoints anyway?

I.e., take the specification of that protocol out of purview of NVO3?
The only thing NVO3 needs to do is:

    - develop a negotiation protocol
    - indicate how to use some subset of encapsulations

If the key issue here is the debate between bitfield and TLV, that
should be taken off the table as an issue.

Joe