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Date:      Mon, 17 Sep 2001 17:40:35 +1200
From:      David Preece <davep@afterswish.com>
To:        freebsd-questions@freebsd.org
Subject:   MTU table?
Message-ID:  <01091717403513.83234@development.wgtn.csg.co.nz>

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Hi,

I have a network consisting of:

Server (mtu1500)<->(mtu1500)gateway(mtu576)<->Client (mtu1500)

The server and gateway are both FreeBSD4.x machines and the client is NT4, 
hence changing MTU is a bit of a mystery, but I digress. So, the first time 
the client connects to the server and the server attempts to send back a 
packet of over 576 bytes, the gateway objects and sends back an ICMP 3(4) 
saying that the packet can't be forwarded until the MTU is reduced to 576. 
The server tries again with the new MTU and all is well. 

The kernel on the server also has the good sense to remember that there's an 
MTU of 576 bytes on that route and doesn't try anything larger in future. 
This would be great *except* that I'm trying to turn the whole thing into a 
factory for ICMP cannot fragment messages. Is there a simple way to flush the 
route->mtu table on the server?

Thanks,
Dave


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