RE: State of play with Shim6 documents

["Henderson, Thomas R" <thomas.r.henderson@boeing.com>]

> -----Original Message-----
> From: Brian E Carpenter [mailto:brc@zurich.ibm.com] 
> Sent: Saturday, January 27, 2007 12:32 PM
> To: Henderson, Thomas R
> Cc: Geoff Huston; shim6-wg; kurtis@kurtis.pp.se
> Subject: Re: State of play with Shim6 documents
> 
> On 2007-01-24 19:06, Henderson, Thomas R wrote:
> >> -----Original Message-----
> 
> ...
> >>
> >>      * TCP Checksum Failure
> >>
> >>            Its not clear what the WG want to do on this. 
> Suggestions?
> >>
> > 
> > I would vote to align the checksum with the locators, under the
> > assumption that defining an alternate probing mechanism to discover
> > these problems is more cumbersome.  If you care strongly 
> enough about
> > using the transport checksum to detect incorrect address 
> rewriting in
> > certain error scenarios, that may argue for putting better error
> > detection in the shim proper, but I'm not sure it is a high enough
> > probability event.
> 
> I have the opposite view. I think we should keep rock solid
> on the notion that shim6 preserves the end to end model as far
> as upper layers are concerned. Fixing the TCP checksum twice,
> on the way in and out of the shim, would be an ugly hack on
> that model, and also the first step towards inserting all
> sorts of ALG functionality in the shim to compensate for
> misbehaving middleboxes.
> 
> Before taking any other decision, I'd want to see firm
> observational evidence that there is a real problem. TCP
> checksums are no business of middleboxes, except for the
> TCP relay case which would probably need to be shim6-aware.
> 

I agree that it would be best to make decision based on operational
experience, but I am suspicious about the future for IPv6 because there
is no IP checksum, so it might encourage routers or middleboxes to
provide transport checksum validation as a feature.

But perhaps it would be prudent to devise an extension only if
shim6-awareness doesn't materialize in practice, and keep it cleaner for
now.

Tom