Re: Smallest Transit MTU

[Iljitsch van Beijnum <iljitsch () muada com>]

On 30-dec-04, at 0:48, Tony Rall wrote:

> Remember that the DF bit is in the IP header - it can be on in any
> protocol.  I know that AIX and my old RH Linux (at least) defaults to
> PMTUD enabled for tcp and udp.  You can even see it in dns lookups.

I'm interested to learn what a poor unsuspecting UDP application does 
when it sends out packets that turn out to be too large? The UDP 
protocol is in no position to limit the packet size. So if the 
application doesn't do it either, the IP layer has to fragment the 
packets. This is exactly what happens with IPv6, but since routers must 
be prepared to fragment in IPv4 anyway, the whole exercise becomes 
fairly pointless...