DHCP client state if rebooted when local DHCPD server is offline?

[Gregory Sloop]

tlfc> Hi Greg

tlfc> On Thu, Aug 14, 2014, at 10:01 AM, Gregory Sloop wrote:
>> I think we need to be a bit more specific. Do you mean:

tlfc> Not sure how exactly to ask, TBH :-/

tlfc> I'm trying to get a handle on what happens if the server's not
tlfc> available, and the LAN client needs to get it's IP address. 
tlfc> Without an assigned/working IP address, bootup seems to choke
tlfc> somtimes, or at least stall for a very long time.  Not
tlfc> *entirely* sure yet if that's lack of IP or lack if intfc.

>> A google search might be insightful too. [Or a search on the list archives.]

tlfc> The problem there is NOT too-little info, but too-much noise. 
tlfc> Finding something relevant/clear is the current challenge.

>> And on that note, what clients? Windows, Linux, Mac etc? And what versions?

tlfc> Linux/64

tlfc> One of (which was my immediately prior question)

tlfc>  dhcpcd (dhcpcd 3.2.3)
tlfc>  dhclient (isc-dhclient-4.2.5-P1)

>> 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.

tlfc> I *think* Simon's link-local solution *might* be the answer.

tlfc> Atm, though, my problem's more basic.  My client can't seem to
tlfc> GET an IP address from the DHCP server even if the server IS up.

tlfc> I keep getting lots of these:

tlfc> ...
tlfc> Aug 14 10:04:31 tgdesktop dhclient[4335]: DHCPDISCOVER on eth0
tlfc> to 255.255.255.255 port 67 interval 2
tlfc> Aug 14 10:04:33 tgdesktop dhclient[4335]: DHCPDISCOVER on eth0
tlfc> to 255.255.255.255 port 67 interval 3
tlfc> Aug 14 10:04:33 tgdesktop ifup-dhcp[4278]: .
tlfc> Aug 14 10:04:36 tgdesktop ifup-dhcp[4278]: .
tlfc> Aug 14 10:04:36 tgdesktop dhclient[4335]: DHCPDISCOVER on eth0
tlfc> to 255.255.255.255 port 67 interval 5
tlfc> Aug 14 10:04:38 tgdesktop ifup-dhcp[4278]: .
tlfc> Aug 14 10:04:41 tgdesktop dhclient[4335]: DHCPDISCOVER on eth0
tlfc> to 255.255.255.255 port 67 interval 12
tlfc> ...

tlfc> then it eventually times out.  Same whether I use dhcpcd or dhclient.

tlfc> WIth static mode, rather than dhcp mode, on my interfaces, everything works perfectly.

It seems clear that there's some problem with the DHCP server, [or perhaps VLAN's or network connectivity.]

How about a quick packet capture to be sure the DHCP server is actually seeing the requests. [I think this is the first, most important step.]
-If it IS seeing them, then there's some configuration problem.
-If it isn't, then figuring out what's preventing the communication from occurring, would be important. [Broadcast filtering, DHCP server and DHCP client on different VLANs without a DHCP helper/relay etc.]

-Greg

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