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Rapid DHCP: Or, how do Macs get on the network so fast?

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354 points timdoug | 1 comments | 12 Jul 11 17:04 UTC | HN request time: 0.22s | source
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dhess ◴[12 Jul 11 19:57 UTC] No.2756257[source]▶
When coming out of sleep, my Macs often get a new computer name in the form of a " (N)" suffix; e.g., a Mac named "vision" will come out of sleep and mysteriously change its name (as reported in System Preferences->Sharing) to "vision (2)", then "vision (3)" after a subsequent sleep, etc.

It's annoying. I wonder if this rapid DHCP implementation has anything to do with that.

replies(1): >>2756448 #
calloc ◴[12 Jul 11 20:39 UTC] No.2756448[source]▶
DHCP allows the computer to send a computer name to the DHCP server, the server can then dynamically set DNS entries based on the computer name.

DHCP is also allowed to send back a new hostname (the reason why on Mac's sometimes depending on the network you are connected to a different hostname is shown on the command line). What is most likely happening here is that your DHCP server is sending you a new hostname because it is not letting your Mac use its old lease for one reason or another.

replies(2): >>2757624 #>>2758389 #
1. dhess ◴[13 Jul 11 03:18 UTC] No.2757624[source]▶
I can't rule that explanation out, but I think it's unlikely in this case: my DHCP server knows the MAC address of all of my machines, uses a static MAC->IP mapping, and doesn't update DNS (which is also static). The IP and hostname (as reported by `hostname`) are always correct; it's just the name as reported in the Sharing preference pane and in Finder from other machines on that network that gets the " (N)" suffix.