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Re: [tcpm] Congestion control in face of ICMP unreachable messages

Ted Faber <faber@ISI.EDU> Fri, 17 August 2007 16:26 UTC

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Date: Fri, 17 Aug 2007 09:25:42 -0700
From: Ted Faber <faber@ISI.EDU>
To: Daniel Schaffrath <daniel.schaffrath@mac.com>
Subject: Re: [tcpm] Congestion control in face of ICMP unreachable messages
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On Fri, Aug 17, 2007 at 06:06:55PM +0200, Daniel Schaffrath wrote:
> Dear Community,
> 
> I was wondering if there are any recommendations regarding congestion  
> control in face of ICMP (host/network) unreachable messages. If I am  
> not mistaken there is nothing in the various TCPM documents... nor in  
> any RFC.
> 
> Maybe you have any pointers?

Sure.  If the code in the destination unreachable message is 2-4 abort
the connection.  Otherwise, don't.  RFC 1122.

I wouldn't use ICMP reachability information in congestion control,
and I don't believe that any standard requires an implementer to do so.
If packets aren't being delivered, the sending endpoint(s) will slow
down pretty dramatically, pretty quickly without intervention.  A
retransmisson timeout puts the endpoint into slow start.

You're still technically required to respond to an ICMP source quench,
but I personally wouldn't.

-- 
Ted Faber
http://www.isi.edu/~faber           PGP: http://www.isi.edu/~faber/pubkeys.asc
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