Subject: Re: [lisp] #7: LISP ETRs ignoring checksum value in LISP UDP outer header on decapsulation

From: [email-masked] (Noel Chiappa)
Date: Fri, 21 Aug 2009 11:29:00 -0400 (EDT)

> From: Sam Hartman <[email-masked]>

    > Unfortunately it seems completely unavoidable as well.
    > * high-end routers seem unable to compute checksums efficiently in hardware
    > * host stacks throw away bad UDP checksums in hardware; for V6, this
    >   often means throwing away 0 checksums
    > ...
    > However it seems that in practice, we will have significant problems
    > with pairings that do not work, especially for IPV6.

Indeed.

My impression is that there is probably _no_ set of UDP checksum choices
which does not have _some_ problems. So we merely get to chose which
problem(s) we will grind our teeth and accept...

	Noel

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From: Margaret Wasserman <[email-masked]>
Date: Fri, 21 Aug 2009 11:56:16 -0400

> problem(s) we will grind our teeth and accept...

True.

There is also the (admittedly less likely) possibility that we will  
weigh all of the UDP checksum-related problems against the cost of  
using a non-UDP encapsulation (the LAG/ECMP problem), and decide that  
is preferable to move to a different encapsulation.  Personally, I am  
not certain I know what the best choice would be, but I do think it is  
very important that we get all of the issues on the table as clearly  
as possible, so that the group can weigh the options and make a well- 
informed decision.

Thanks for your help so far in doing just that.

Margaret