North American Network Operators Group

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MTU discovery problems in the Internet?

  • From: Jamshid Mahdavi
  • Date: Mon Feb 12 08:58:56 1996


In the last few days I have noticed two sites, quite by accident, to
which MTU discovery does not work correctly.  In one case the router
which failed blackholed the traffic, and in the other case, the router
returned an MTU value which is garbage (Friday I got 18K, today I get

Many sites depend on MTU discovery working properly, and the need for
MTU discovery is not going away!  I ask all of you provider types out
there to please look over RFC1191 (it is short).  If you don't have
tools to diagnose MTU discovery problems, you can pull down 

which includes a -M switch for MTU discovery.