Subject: Re: [Spud] New Version Notification for draft-touch-tsvwg-udp-options-01.txt

From: "C. M. Heard" <[email-masked]>
Date: Fri, 14 Aug 2015 11:35:08 -0700

On 7/22/2015 09:52 AM, Joe Touch wrote:
> On 7/21/2015 11:22 PM, Brian Trammell wrote:
> > hi Joe,
> >
> > Thanks for this draft; I appreciate the elegant redundancy-reducing
> > length hack. :)
> >
> > Data in this case is, I know, hard to come by, but would you have
> > any feel for how much stuff out there will just break when they see an
> > inconsistency between IP and UDP length information?
>
> I have students starting this fall who will look into this and do some
> tests. We have no information yet.

In an off-list e-mail exchange with Joe a couple of weeks ago, I noted
that every host stack implementation whose code I have inspected simply
ignores bytes that are past the UDP length but within the IP payload
length.  The BSD-derived stacks trim the excess bytes before the data
is passed to the application via the sockets interface.  However, one
embedded stack I have seen (which does not use a sockets API) makes
all data available to the application, including the UDP header, and
lets the application deal with excess bytes as it sees fit.

I have zero information on the behavior of middleboxes (NAT/NAPT).

Assuming that Joe's tests confirm these observations for both end
systems and middleboxes, then the proposed UDP option trailer should be
incrementally deployable as long as all options therein can be safely
ignored if not understood.  The degree of utility (or, at least, the
length of time needed to make them useful) will of course depend
strongly on whether middleboxes trim the trailer or leave it intact;
if the prevalent middlebox practice is to trim it, then they won't be
useful without updating middleboxes as well as end systems.

Also, Joe, if you and your students have the time and resources to look at
what middleboxes do with UDP packets where the IP header indicates a
shorter length than the UDP header, that would be useful information, as it
could open up a possible means to incorporate fragmentation in the UDP
layer, independent of whether or not an options trailer is present.

Mike Heard