SUMMARY: Same ethernet address on two interfaces.

From: Brian Utterback (
Date: Thu Mar 18 1993 - 01:27:43 CST

Many thanks to all who replied. While I am now assured that nothing is wrong,
I am still perplexed.

My original question was that I had the same ethernet MAC address on two
physical interfaces, when my understanding was that interfaces had unique
addresses assigned by the manufacturer.

All of the responses said that the ethernet address was loaded from an ID
in the prom and was set on all the interfaces. Since the interfaces are on
separate physical wires, the requirement that the address be unique on a wire
is maintained.

This brings up some questions in my mind. What about rarp requests? If the
interfaces have the same MAC address and different IP address, doesn't this
screw up the rarp protocol? How to you enter the addresses in the ethers file?

BTW, some of you thought the two interfaces were on the same physical wire, but
that was not the case.

Thanks to:

Casper Dik <>
Geert Jan de Groot <>
Mr T Crummey (DIJ) <> (Eckhard Rueggeberg) (Dick St.Peters)
Patrick O'Callaghan <> (Peter Sivo) (Daniel Trinkle)
Chip Christian <> (Ed Strong)
obs! (E. Mike Durbin) (Evan L. Marcus [Fusion Services Group])
hyder@niwot.scd.ucar.EDU (Paul Hyder)
todd@flex1.Eng.McMaster.CA (Todd Pfaff) (Russ Poffenberger) (Harald van Breederode) (Ken Bibb)

as well as to those whose messages haven't gotten here yet.

Brian Utterback Manager Technical Networks
Mercury Computer Systems, Inc. (508) 256-1300x168
199 Riverneck Road (508) 256-3599 FAX
Chelmsford, MA 01824 Always mount a scratch monkey.

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