decnet phase V

Charles Hedrick (
Sat, 8 Aug 87 19:00:59 EDT

Sorry, I should have been more clear about the phase V DECnet
addressing. First let me note that I am basing this on a paper given
a few months ago at an IETF meeting. I have not seen full
documentation for phase V. According to this paper the basic DECnet
address will involve 2 bytes of area number and 6 bytes of system ID.
"DEC uses Ethernet absolute host ids in this field to ease address
administration. The only requirement, however, is that the ID be
unique within an area for level 1 ISs and ESs, and unique within the
domain for level 2 ISs". It appears that the ISO IS-ES (the ISO
equivalent to ARP) is used, so that there would be no problem handling
machines whose DECnet address differs from the Ethernet address.
There are other features of their addressing that makes it somewhat
more general than what is implied by the description here, but the
document is too vague for me to be sure what it means. In particular,
an entire set of addresses, using the full 8 bytes described above, is
a "domain". There is some provision for connecting multiple domains,
using fixed routing tables at the border nodes. The DECnet format is
designed to use only 8 bytes in a fixed portion of the full ISO
address, in order to facilitate hashing. There was also a comment in
the talk that if necessary other address formats could be used, but
handling them would be less efficient. The upshot is that I know of
no problems with phase V DECnet addressing. Maybe I'll find some once
I see it in detail, of course.

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