jmg@cernvax.UUCP (07/16/86)
First, the problem. We have many Ethernets bridged together with mac-level bridges. The various bridges note all passing Ethernet source and destination addresses, and so I can get lists of addresses on each Ethernet segment. Some are hardware, others are software: the latter ought to include the locally-administered bit, but I have my doubts. Most of the hardware addresses have obvious patterns, in the first half of the address. What I find, however, is that after a time there are lots of addresses which I don't recognise at all. Part of the problem is that it is very hard to keep up-to-date with who is connecting what onto the Ethernets, part may be software problems in our home-built bridges, and part may be maverick users creating their own source addresses by software. Needless to say, the anonymous nature of Ethernet makes it difficult to track down these mavericks: all ideas will be welcome to me and any other administrators of large bridged Ethernets. A partial solution. As mentioned, there are normally patterns to Ethernet hardware addresses, according to address ranges handed out originally by Xerox, now by ?. On mine, I see options for the top half of the addresses as 020701 Interlan 0800xx (xx = 02, 26, 2b, 4e) 0260xx (xx = 86, 8c) 000203 0000cc plus lots of others, pretty random. The locally-administered ones are virtually all DECNET (0a004e), which we have well under control. We could adapt our bridges not to pass on any Ethernet packet with a source address which does not match certain criteria (i.e. an address which looks as if it will be meaningful). In this context I have a fair idea of what makes of Ethernet controllers are in use. I can also wear my hat of administrator, and ensure that all locally administered addresses are cleared with me, and hence have a known form. Can I do the same with such as the LAN-Bridge 100? A need. I could do with a list of what Ethernet ranges of addresses have been assigned to who. Does anyone have such a list, in computer-readable form, preferably updated at regular intervals? Presumably Xerox did have one at one time. Mike Gerard