Re: [dccp] PMTU issues

[Pekka Savola <pekkas@netcore.fi>]

Everyone,

Please discontinue this discussion at v6ops@ops.ietf.org list.

Thanks,
 Pekka
  writing as v6-ops co-chair

On Wed, 19 Nov 2003, Eddie Kohler wrote:
> > It's also possible for DCCP to get a better initial estimate of the PMTU,
> > and apparently there are other problems with the current DCCP PMTUD
> > mechanism (using ICMP "can't fragment" messages).  
> 
> Yes -- The current draft tries to make clear (but fails to) that a new,
> PLPMTUD-style MTU discovery mechanism is acceptable. There are API problems
> with such a scheme, but we absolutely allow it.
> 
> If you can accept an extra RTT or two at connection initiation time, I
> think you can do pretty well:
> 
>     Request -->
>             <-- Response
>     then, all in 1 RTT:
>     Padded Sync(512 bytes) -->     /* actual #s would need to fit CC
>     Padded Sync(1280 bytes) -->	       mechanism */
>     Padded Sync(4000 bytes) -->
>             <-- SyncReply(1)	   /* SyncReplies sent only for those
> 	    <-- SyncReply(2)	      packets that got through */
> 	    <-- SyncReply(3)
>             
> > So, my question for the DCCP people, is it worth changing DCCP PMTUD?
> 
> It's certainly worth describing it better, and perhaps mentioning a set of
> acceptable procedures.  Have you any suggestions for useful procedures
> here?
> 
> Eddie
> 
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-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings