Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!pyrdc!pyrnj!bartal!monymsys!sonyd1.Broadcast.Sony.COM!blilly.UUCP!balilly.UUCP!bruce From: bruce@balilly.UUCP (Bruce Lilly) Newsgroups: comp.protocols.tcp-ip Subject: Re: Ethernet Address Uniqueness... Keywords: Ethernet addresses uniqueness Message-ID: <1990Oct11.031433.3032@blilly.UUCP> Date: 11 Oct 90 03:14:33 GMT References: Sender: news@blilly.UUCP (News Administrator) Organization: Bruce Lilly, Flushing, NY Lines: 49 In article linegar@bwdls49.bnr.ca (Derick Linegar) writes: > >[ ... ] > Now I've been searching the RFC and IEEE docs and I cannot >find any documentation that sort of says that Ethernet Addresses are assigned >to Ethernet boards, not hosts. > >Anyone have an idea where it might be. I cannot go back to the vendor and >say > > " .... well everyone *knows* that ethernet addresses *must* be unique..." ``For information on global (U) address administration contact the Secretary, IEEE Standards Board, 345 East 47 Street, New York, NY 10017.'' (Footnote on page 26 of ANSI/IEEE Standard 802.3-1985 ISO/DIS 8802/3) My recollection is that each manufacturer is assigned a group of addresses and is expected to make the hardware address unique for each interface. As has been pointed out (for the specific case of DECnet) it is also possible to override the hardware address via software, and that may be a part of your problem. The IEEE Secretary ought to be able to clarify this situation, and may be able to tell you what range of addresses are assigned to your particular vendor. Late flash: after checking several references, I found: ``14.4.2 Ethernet addresses Host computers on Ethernet are identified by two addresses, the Ethernet address (a 48-bit hardware address) and an IP or software address. Ethernet addresses are guaranteed unique because vendors building Ethernet interfaces have a set of addresses assigned to them. The IEEE Standards Board in New York City assigns the first 24 bits to a manufacturer, which then allocates the last 24 bits sequentially. The address is either built into the interface board or stored in ROM on the board.'' (From _UNIX(R)_System_Administration_Handbook_ by Nemeth, Snyder, and Seebass, published by Prentice-Hall, p. 243) An excellent book, by the way, although it is heavily biased toward BSD. Note however that the IEEE standard permits either 16-bit or 48-bit addresses, so don't take that too literally. Hope this helps. -- Bruce Lilly blilly!balilly!bruce@sonyd1.Broadcast.Sony.COM