<html><head><title>Re: DHCP client state if rebooted when local DHCPD server is offline?</title>
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<span style=" font-family:'courier new'; font-size: 9pt; color: #800000;"><b>tlfc> I understand that if my LAN's dhcpd server is up, when any<br>
tlfc> client on the lan is rebooted, it'll pick up its lease & IP address.<br>
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tlfc> What happens on the client if it reboots when the LAN's dhcpd<br>
tlfc> is stopped, NOT serving dhcp info/leases?<br>
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tlfc> Does the client come up in the last known state? With the<br>
tlfc> last-used IP addresses? Or, instead, default or random IP address info?<br>
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tlfc> I'm trying to understand what happens to daemons/listeners on a<br>
tlfc> lan client, bound to a specific IP address, in that ^^ case.<br>
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</b><span style=" color: #000000;">I think we need to be a bit more specific. Do you mean:<br>
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. <br>
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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.]<br>
And on that note, what clients? Windows, Linux, Mac etc? And what versions?<br>
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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.<br>
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-Greg</td>
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<span style=" font-family:'Courier New'; font-size: 9pt;">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.<br>
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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.]<br>
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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.<br>
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See:<br>
</span><a style=" font-family:'Courier New'; font-size: 9pt;" href="https://www.ietf.org/rfc/rfc2131.txt">https://www.ietf.org/rfc/rfc2131.txt</a> <br>
<a style=" font-family:'Courier New'; font-size: 9pt;" href="http://www.tcpipguide.com/free/t_DHCPLeaseRenewalandRebindingProcesses-2.htm">http://www.tcpipguide.com/free/t_DHCPLeaseRenewalandRebindingProcesses-2.htm</a> <br>
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<span style=" font-family:'Courier New'; font-size: 9pt;">Again, someone more knowledgeable than I may be able to fill in more detail.<br>
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-Greg<br>
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