Re: IBM TCP.


Ken Rossman (sy.Ken@CU20B.COLUMBIA.EDU)
Mon 3 Aug 87 16:54:35-EDT


We've had a reasonable amount of experience with medium to large DECnet
networks here at Columbia. We have our own internal network, and we also
connect to various other sites who also have their own DECnet networks.

I am not sure how Ethernet addresses are administered (I was under the
impression that one or more of the larger corporations plugging Ethernet
divvy up the board addresses by board manufacturer). In any case, the
first four bytes of a DECnet transformed Ethernet address are, by some
"global allocation" method, preassigned to DEC as I understand it.

Since, as David Plummer points out, DECnet IV only currently supports 64K
nodes on any single DECnet (well, really 63K --- area 0 is not a real area,
and generally designates Phase III nodes), it doesn't really matter whether
the limitation occurs at the ethernet addressing level or at the DECnet
addressing level. The limit is still the same -- 63K.

There is no "global" administration of DECnet areas that I know of. I deal
them out for CCnet (the DECnet here that spans the CU campus and several
other schools). In fact, awhile back, we were looking at connecting to
other large DECnets (PHYSnet, I think, was the name of one of them, or
something close to that), and we were given AN area to live in by the
PHYSnet administrators. Since we were already multi-area, this made it
basically impossible for us to connect with them, and we bagged the idea.

As for DECnet, ARP, and ethernet addresses, Ultrix handles this just fine.
We just make sure that DECnet comes up before IP does, so that the ethernet
address that ARP uses is the DECnet-transformed one. /Ken
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