This is a discussion on Re: [fw-wiz] How automate firewall tests - Firewalls ; Hi! > Sure, but not many folks are downstream of small MTU serial links anymore, > so if you set your external link to frag at 1492 or less (down to the > minumum of 576 if you'd like ~100% ...
> Sure, but not many folks are downstream of small MTU serial links anymore,
> so if you set your external link to frag at 1492 or less (down to the
> minumum of 576 if you'd like ~100% success,)
Got it. But 576 doesn't guarantee 100% success, even if you have
a fair chance ;-)
IIRC any IP implementation must be able to receive at least 576
bytes sized frames. But there is no mandation of a minimum path MTU
of that size. 256 bytes or something in that order was common on
dialup modem links.
> But since you control PMTU on your network, you can simply shrink it
> enough and allow the ICMP traffic between trusted nodes only. Solves the
I was thinking of the not so knowledgable server/firewall admin
blocking ICMP without those measures. And, what's so bad about
ICMP "df needed" messages? Of course I'm not proposing to allow _all_
types of ICMP through.
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