Submit Hint Search The Forums LinksStatsPollsHeadlinesRSS
14,000 hints and counting!


Click here to return to the 'Actually...' hint
The following comments are owned by whoever posted them. This site is not responsible for what they say.
Actually...
Authored by: Cadre on May 17, '01 09:00:57PM

The purpose of a Mac address isn't so that all ethernet cards can be positively identified. Mac addresses are different so that communication over the IP layer is possible. Mac addresses can be the same (though, unless you are manually changing them, this will never happen) they just can't be the same on the same LAN.

It used to be that one could change the mac address just by typing "ifconfig en0 lladdr new_mac_address" with some cards. On others you couldn't, you would have to patch a couple system calls (do a search on google for setmac.c and/or module_3.0) and that would also work. I haven't run across a way to do with with MacOS X and the gigabit cards though.



[ Reply to This | # ]
Re:Actually...
Authored by: _merlin on May 18, '01 01:55:37AM

You seem to have misunderstood what I meant. I meant that a MAC address is supposed to be unique, so that even if you created a LAN containing every network card in the universe, they would all have a different MAC address, and therefore be individually distinguishable. If two had the same MAC address, the messages destined for either of them would be received by both, and messages from either of them would appear to be coming from a single card. This is why each and every network card manufactured has a MAC address hard-coded into it.

The ability of software to change MAC addresses does not change these hard-coded addresses. It merely makes a temporary change to the address the card is using. If you reset the card, it will return to its hard-coded address.

In summary, I do realise that it is possible to change the address that a card uses, it is not possible to change its hard-coded address. The way cable modems latch onto a single MAC address is not a particularly good security measure. It doesn't take into consideration the fact that a user may upgrade their network card or computer, and doesn't allow a user to share one modem between two or more computers. Changing our MAC addresses to circumvent this shortcoming doesn't solve the problem. It is merely hiding from it. Let's tell the cable modem manufacturers what we think of this scheme, and pressure them to change.

Vasantha Crabb



[ Reply to This | # ]