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.t.... 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 PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1