Subject: Don't fragment IP packets (DF)
To: None <port-sparc@NetBSD.ORG>
From: Oliver Paulzen <>
List: port-sparc
Date: 02/12/1997 17:35:53
Hello NetBSD-Users!

I've got a SUN IPX running NetBSD-1.2. My 'internet' router is an i386
running FreeBSD-2.1.5 connected to another FreeBSD-PC using a leased line 
with PPP over USR modems. The ppp-devices' MTU/MRU is 552.
Now i've got the problem that when the NetBSD (even SunOS has this)
machine transmits or receives Data through the PPP-line (e.g. UUCP to
poll news), the IP-Packets gets fragmented as the MTU/MRU of le0 is
much bigger than 552. This makes traffic accounting not that easy and
I fear that it's not very fast...
I know that FreeBSD does a kind of MTU/MRU-probing: It sends packets
to the destination host starting with a big size and then with smaller
ones until the packets didn't got fragmented so it 'guesses' the
minimal MTU/MRU on the way to the destination host. Then it sends the
data with this packet size and adds the 'DF' flag to each IP-Header
which forces the router on it's way to not fragment the packet.

My question: is there any possibility in NetBSD (kernel?) to get this
'DF' flag send with each packet or to 'probe' the MRU/MTU values of
the connection to get only unfragmented IP packets?

Many thanx in advance

     opp@MuFFiN.Org    +49-177-2009481

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