Re: ARP on FDDI


David C. Plummer (DCP@QUABBIN.SCRC.Symbolics.COM)
Mon, 16 Nov 87 09:19 EST


    Date: Mon, 9 Nov 87 17:57 EST
    From: Kastenholz@MIT-Multics.ARPA

    There is a rather simplistic solution to the 16 vs 48 bit FDDI address
    problem - assign two physical hardware types to FDDI - one for 16 bit
    addresses and one for 48 bit addresses.

    This may violate some underlying deep philosophical intent of ARP, but
    it looks like it should work.

If being the author of ARP means anything after four years... The type
hardware types sounds completely reasonable to me. From the scant
readings I've seen about FDDI, it seems that there are really two
distinct versions (one with 16 bit addresses and one with 48) and they
cannot coexist on the same cable, lest they confuse each other. Even if
they do/could coexist, I see no reason they shouldn't be considered
separate for the purposes of ARP hardware type.

It is also possible and allowable to dispatch off of both the hardware
type and the hardware length, provided there is only one possible
semantics after the last dispatch. I suspect many implementations,
including the ones I've written, only dispatch off of the hardware type
and check the length for consistency.

>From this 5 minutes of thought, I would opt for two hardware types,
perhaps called FDDI-16 and FDDI-48.



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