Ethernet Address Space


art@acc.arpa
11 Aug 87 13:46:00 PST


>It would seem to me that it would be hopelessly difficult to try to
>administer a flat global set of ethernet addresses, and that some sort of
>mechanism, such as the global/local bits at the beginning would have to
>exist. In any case, regardless of how a spec says it SHOULD be, the real
>world appears to be allocating blocks of ethernet addresses to vendors to
>be used as they (or their customers) see fit.

Vendors are ASSIGNED blocks of addresses which they are responsible for
assigning to their interface boards. When a block is exhausted, another
can be acquired (from Xerox originally, IEEE now). DEC is one of the few
I know of that has more than on assigned block (SUN probably does by now).

>Along slightly different lines, I fail to see how the global ethernet
>addressing scheme, whether managed as a flat address space or in some
>hierarchical fashion, hasn't blown up yet. I mean there just aren't that
>many addresses available. Just as an isolated example, what happens to
>ethernet addresses on failing boards? We've probably had the ethernet
>board on one of our -20's replaced three times already. Am I to believe
>that DEC Field Service records these hardware addresses, and when bad
>boards come back that can't be repaired, they tell some global address
>administrator that this particular hardware address has now been freed and
>can be used again?

I don't think that this is a problem yet. The Ethernet addresses are 48 bits
long, minus one or two for format flags. This still leaves roughly
64 TRILLION possibilities. Even if the address space is only 0.01% utilized,
that leaves roughly 6 BILLION Ethernet interfaces.

                                                Art Berggreen
                                                art@acc.arpa

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