On Mon, 09 Dec 2002 00:34:20 +0000 (GMT) Andrew Errington <[EMAIL PROTECTED]> wrote:
> This is interesting. What kind of things break? We were building an > IP enabled embedded device, and we had the IP address set, but not the > MAC address. Some things broke (as in some other things on our > network), but when we put a valid MAC address in they became unbroke. > In the invalid MAC address the first two bytes were not 00. > > Do you know what problems are likely to occur, or can you suggest a > place where I might find out what they might be? The first bit is used to distinguish individual addresses from group addresses, and the second bit separates globally- and locally-administered addresses. These are followed by the organizationally unique identifier (OUI, a 22- bit field assigned by the IEEE) and the organizationally unique address (OUA, a 24-bit number assigned by the manufacturer). For a normal Ethernet frame the first 2 bits are 0. If the first bit is set you are doing an eth "multicast". If you device is doing IP over ethernet you need to have a valid MAC address (you may want to "generate" a valid one without registering with the IEEE for testing purposes, a company I worked for and that produces dsl modems chips used this approach). Cheers -- Delio Brignoli I'm looking for a job (sw engineer/developer) in New Zealand, pls take a look at my profile: http://www.drlinux.it/profile.html
