DHCP client state if rebooted when local DHCPD server is offline?
gregs at sloop.net
Thu Aug 14 17:17:30 UTC 2014
tlfc> I understand that if my LAN's dhcpd server is up, when any
tlfc> client on the lan is rebooted, it'll pick up its lease & IP address.
tlfc> What happens on the client if it reboots when the LAN's dhcpd
tlfc> is stopped, NOT serving dhcp info/leases?
tlfc> Does the client come up in the last known state? With the
tlfc> last-used IP addresses? Or, instead, default or random IP address info?
tlfc> I'm trying to understand what happens to daemons/listeners on a
tlfc> lan client, bound to a specific IP address, in that ^^ case.
I think we need to be a bit more specific. Do you mean:
The station/client gets, lets say, a 4 hour lease. After 20m, the station is rebooted. Does the station continue to use the "old" lease that it still has 3:40 left before it expires? [I think this is client dependent. Windows may work differently than Linux etc.] I *think* thoretically, that the station _could_ continue to use the old lease until it expires. But I don't believe it HAS to do so. And I don't know how particular clients handle these things in practicality.
Perhaps someone who knows how different clients work in practice can chime in. A google search might be insightful too. [Or a search on the list archives.]
And on that note, what clients? Windows, Linux, Mac etc? And what versions?
If you mean, the lease is expired before the station is brought back up again, then it will need a new lease from the DHCP server.
As a follow-up. I know that some Windows machines will continue to hold the unexpired lease over a reboot, and that to force a check with the DHCP server you'll have to do a ipconfig /release | ipconfig /renew to do so.
So, in practice, in at least some versions of Windows, they will continue to hold the lease. [Windows does/attempts a renewal at 50% of life remaining, and at 87% [IIRC] it will then do a broadcast to any DHCP server to attempt to get a new address/renewal. I may some some fine detail not exactly correct, but that's approximately right.]
But I don't know if this behavior is part of an RFC or simply because that's the way they do it. I believe the exact times [say 50% of lease gone before renewal] is simply a matter of practice, not dictated by RFC.
Again, someone more knowledgeable than I may be able to fill in more detail.
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