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To: Charles Henrich <henrich@crh.cl.msu.edu>
cc: fenner@parc.xerox.com (Bill Fenner), freebsd-bugs@freebsd.org
Subject: Re: MTU > 1500 ? what the.. 
In-reply-to: Your message of "Sun, 09 Mar 97 21:07:05 PST."
             <199703100507.AAA00841@crh.cl.msu.edu> 
Date: Sun, 9 Mar 1997 22:37:04 PST
From: Bill Fenner <fenner@parc.xerox.com>
Message-Id: <97Mar9.223713pst.177476@crevenia.parc.xerox.com>
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The actual maximum Ethernet packet size is 1516 bytes (1500 bytes of
payload, 6 bytes of src, 6 bytes of dst, 2 bytes of type, and 2 bytes
of CRC).  tcpdump doesn't report the CRC which is why you see 1514.

Sounds like you have a broken router which isn't sending ICMP
packet-too-big errors.  I wonder if the traceroute that someone
submitted as a port does MTU discovery; you can use an MTU-discovering
traceroute to discover such broken routers.

  Bill