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Re: exchange point media (was: Re: MAE-EAST Moving? ...)
From: John Hall <j.hall () f5 com>
Date: Thu, 22 Jun 2000 11:39:14 -0700

This is a problem for many switches that support non-ethernet interfaces.
RFC1191 does not apply to switches (only routers), but it probably should.
I've run into this problem with switches from Fore and Cabletron.  I would
bet that this is a problem for most switches.


Jeff Haas wrote:
Should one install a (fast|gig)ethernet card into one's Gigaswitch
and said switch have FDDI interfaces, the switch will go from having
a 4500+ byte MTU to a 1500 byte MTU.  This is even between FDDI card
to FDDI card on the same switch.

The switch will happily fragment the packet if you leave DF off.
However, if you turn it on, the switch will drop the packet silently.
The switch is unable to generate ICMP and route it back to the

Given all of this, PMTU-D breaks in these circumstances.
Jeffrey Haas - Merit RSng project - jeffhaas () merit edu

John Hall <j.hall () f5 com>                                     F5 Networks, Inc.
Senior Test Engineer                                          206-505-0800

It is up to us to produce better-quality movies.
        -- Lloyd Kaufman, producer of "Stuff Stephanie in the Incinerator"

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