IPv4 address length technical design

Fred Baker (fred) fred at cisco.com
Sat Oct 6 01:06:06 UTC 2012

On Oct 5, 2012, at 4:34 PM, Barry Shein wrote:

> Well, XNS (Xerox Networking System from PARC) used basically MAC
> addresses. Less a demonstration of success than that it has been
> tried. But it's where ethernet MAC addresses come from, they're just
> XNS addresses and maybe this has changed but Xerox used to manage the
> master 802 OUI list and are assigned OUIs 000000...000009. Not
> insignificant in their effect.

You need a memory refresh. XNS used a three part address: network number, host identifier, and socket number. "Socket" was in essence the TCP/UDP Port Number. the host identifier was as you say a 48 bit number and generally took as its value the MAC address on one of the interfaces - and the same MAC address was used on all interfaces. Hence, no need for ARP/ND. The network number was a 32 bit number assigned to a LAN subnet. A multihomed host essentially implemented ILNP. 

The issue with the network number was, of course, that it couldn't be aggregated in any useful way. But XNS was not ethernet bridging on a wide scale.

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