jas@MONK.PROTEON.COM (John A. Shriver) (03/07/88)
The AA:00:04:xx:xx addresses are indeed DECnet Phase IV addresses. The low two bytes are the 16-bit DECnet node address, with the low 10 bits node, and the high 6 bits area. It is inserted in PDP-11/VAX byte order, so it looks backwards printed Ethernet/big-indian. (All of DECnet uses PDP-11 byte order.) Note that they are setting the locally administered bit in the prefix (02 in the first byte), so they are not claiming that these addresses are globally unique. Presumably they paid their $300 for that block from Xerox. Well, from my understanding, the architects did not know that ARP existed, so that option did not present itself to them. They chose this scheme because it was simple. It is documented in "DECnet DNA Phase IV Ethernet Data Link Functional Specification", AA-Y298A-TK. This is not required in DECnet Phase V. Since it will use ISO CLNS as a network protocol, it will support big long ISO addresses (12 bytes?). The little old 6 byte Ethernet address gets wrapped up somewhere inside these big addresses, so they can use the PROM address. Phase V will also eliminate their need for name-to-address translation tables, by provide a well-designed naming service. It looks much more flexible and dynamic than the Internet's Domain Name System.