Re: IP Fragmentation

[Fernando Gont <fernando () gont com ar>]

At 08:44 p.m. 28/08/2008, Glen Kent wrote:

> I understand that routers usually must send this error only when a
> fragmentation is required and they recieve a packet with DF bit set.
> However, in this case this router would drop the packet (for it doesnt
> support fragmentation) and sending an ICMP error back to the host,
> warning it that its packets will get dropped seems to be a better
> option.
>
> OTOH, what do most of the implementations do if they send a regular IP
> packet and receive an ICMP dest unreachable - Fragmentation reqd
> message back? Do they fragment this packet and then send it out, or
> this message is silently ignored?

You may want to have a look at this IETF I-D: 
http://www.gont.com.ar/drafts/icmp-attacks/draft-ietf-tcpm-icmp-attacks-03.txt. 
The PMTUD modification described in the draft ships (at least) in 
OpenBSD and NetBSD.

Thanks!

Kind regards,

--
Fernando Gont
e-mail: fernando () gont com ar || fgont () acm org
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