3 ms·
You normally would just pick a random one, and you have probability near 1/2⁴⁸ of colliding with each other device on your LAN.
by schoen 7y ago
You normally would just pick a random one, and you have probability near 1/2⁴⁸ of colliding with each other device on your LAN.
- joshvm 7y agoIt may be more like one in 2^24. The first 24 bits are allocated for other things, so it depends how the address is randomised (eg if you keep the manufacturer bits). Though if you report a totally random address it probably will be closer to 2^48. https://www.ionos.co.uk/digitalguide/server/know-how/mac-address/ https://www.ionos.co.uk/digitalguide/server/know-how/mac-add...
- zamadatix 7y agoYou should really be setting the "Locally Administered" bit to 1 when generating random MACs. This combined with the unicast bit should give you 2^46 possibilities without the chance to collide with a globally assigned address at all. https://www.hellion.org.uk/cgi-bin/randmac.pl https://www.hellion.org.uk/cgi-bin/randmac.pl
- AndyMcConachie 7y agoThe lowest order bit of the first byte must be 0 for a station MAC. If it is 1 then it is a multicast MAC which can never be a source MAC. A MAC can also never be all zeros. So I think it works out to something like (2^47)-1. I'm probably forgetting some other specifics so it might even be lower than that. There's a bunch of incorrect information on the link in parent. A simple example is that 01:00:5e:00:00:01 is NOT a valid source MAC address.