Subject: Re: ip reassembly time exceeded?
To: None <current-users@NetBSD.ORG>
From: Olaf Seibert <>
List: current-users
Date: 01/30/1997 16:08:00
In <> (Christoph Badura) writes:
>The reason it works from your PPP gateway but not from the machines
>behind it is that when sending from the PPP gateway the kernel send a
>256 byte TCP segment (296 byte IP packet) because it knows the that
>the segment is going out over interface with the 296 byte MTU.  For
>the systems behind your gateway, the kernel only knows that it is
>sending via a gateway, so it uses a 512 byte TCP segment (which
>clearly shows up in your tcpdump output).  The gateway then fragments
>the 552 byte packet into two IP fragments because of the 296 byte MTU
>on the PPP link.
>Why the Microsoft system sends you an "ip reassembly time exceed"
>message is still an open question.  Perhaps you're experiencing a high
>rate of packet loss somewhere on the path.  Perhaps there's a
>misconfigured router dropping certain IP fragments.  Perhaps MS TCP/IP
>stack is broken.

My guess is that M$'s reasoning is about as follows. (Just a guess of
course.) It receives a bunch of fragments and reassembles them. It gets
a datagram that is smaller than the 576 bytes and thinks "well, that's
so small, why would anybody want to fragment that? Let's wait for some

___ Olaf 'Rhialto' Seibert      D787B44DFC896063 4CBB95A5BD1DAA96 
\X/ Don't dream it, Be it