Subject: Re: [lisp] Suggested UDP checksum text

From: [email-masked] (Noel Chiappa)
Date: Fri, 11 Sep 2009 15:20:25 -0400 (EDT)

Dino, as requested:

    > From: "Joel M. Halpern" <[email-masked]>

    > UDP Checksum: this field MAY be transmitted as zero by an ITR.

I'm OK with all the rest of this text, but would like to change this first
"MAY" to "SHOULD". I have discussed this extensively offline with a couple of
the 'usual suspects' in the WG, and they are OK with it.

I can forward extracts of that exchange (which amounts to a long examination
of the whole philosophy of checksums at various levels in the stack) to
anyone who is interested, but the bottom line is that the UDP checksum in the
encapsulation does not perform any useful function _for the encapsulated
packet_, and I would like to make it plain to less-knowledgable readers that
that is so, and changing from a MAY to a SHOULD does that, while changing
reality on the ground little (the two terms are almost interchangeable, in
terms of their effect).

	No0el

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From: Dino Farinacci <[email-masked]>
Date: Fri, 11 Sep 2009 12:26:46 -0700

> the 'usual suspects' in the WG, and they are OK with it.

I can make this change but it doesn't really leave enough time for  
people to discuss it and we are at the deadline. Even though we have  
discussed this to death.

So I propose this;

(1) Make this change.
(2) Post -04 now. There are a lot of changes and we need to post it.
(3) Any other open issues can be addressed in the -05 spec which we  
can open up in the coming weeks.

I hope that is reasonable for everyone.

> reality on the ground little (the two terms are almost  

I trust and believe you Noel. The question is solely on consensus.

Dino

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From: Margaret Wasserman <[email-masked]>
Date: Fri, 11 Sep 2009 15:44:05 -0400

> the 'usual suspects' in the WG, and they are OK with it.

My actual statement was that I prefer MAY, but I am not going to lose  
sleep over it either way.

I also personally prefer a "SHOULD" for IPv6 ETRs to accept incoming  
packets with a zero checksum (to support implementation on existing  
desktop systems), but I understand that others' opinions differ.

One other thing that I _do_ think we need to understand before we can  
reach fully informed consensus on this issue is exactly what draft- 
eubanks-chimento... (AKA [UDP-TUNNEL] says (or, perhaps more  
importantly, what it doesn't say)...
I only recently read UDP-TUNNELS well enough to know what it actually  
says in detail.
It does _not_ say that a LISP ITR can use zero UDP checksums for all  
IPv6 encapsulated traffic.  In particular, it places the following  
restrictions on the use of zero UDP checksums in IPv6/UDP tunnels:
o An inner IPv4 packet with a UDP checksum equal to 0 must not be  
tunneled.
o Non-IP inner packets must have a CRC or other mechanism for checking  
packet integrity.
o Other tunneling protcocols that use the UDP checksum equal to 0 MUST  
NOT be tunneled themselves, even if more deeply encapsulated packets  
have checksums or other integrity checking mechanisms.
So, the UDP-TUNNEL draft will require ITRs to inspect all packets that  
are being encapsulated to make sure that they have integrity checking  
enabled before encapsulating them in IPv6/UDP with a zero UDP  
checksum.  Practically, this means that ITRs will have to be prepared  
to calculate UDP checksums for IPv6/UDP outer headers for all  
encapsulated packets that do not use TCP, SCTP or UDP with non-zero  
checksums.
It will also require that UDP checksums be set to non-zero values  
whenever LISP is tunneled inside LISP.
Has everyone else who is agreeing to the UDP checksum text read the  
UDP-TUNNEL draft?  Are you comfortable with what it says?
Do folks think we need to say something more specific about the [UDP- 
TUNNEL] requirements in the LISP document to make this clearer?
Margaret

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From: Marshall Eubanks <[email-masked]>
Date: Fri, 11 Sep 2009 16:46:38 -0400

Your proposal for -04 WFM

On Sep 11, 2009, at 3:26 PM, Dino Farinacci wrote:

> _______________________________________________
> lisp mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/lisp
>

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From: David Meyer <[email-masked]>
Date: Fri, 11 Sep 2009 13:48:04 -0700

> Your proposal for -04 WFM

+1

Dave

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From: Sam Hartman <[email-masked]>
Date: Fri, 11 Sep 2009 18:25:11 -0400

Dino, I have some concerns about the UDP text that I'd like to discuss
with Darrel; please wait for us.