Comment 6 for bug 1196975

I will see if I can dig up the logs, but this happened a while ago and I only got around to filing this bug now. Anyway, what happened on dozens of machines (might have been hundreds):
Machine has a working ethernet connection (to the switch)
The network itself works reliably for the whole time.
The DHCP servers fail for a prolonged timespan (several hours, long enough for the leases of a percentage of the machines to expire).
Client machines which retained a valid lease might have tried to renew (renewal time << expiry time) and failed, but dhclient kept going.
At some point, the leases for a number of machines expired.
DHCP servers came back up.
Machines that still had valid leases at this point just renewed and worked as expected.
Machines with expired leases didn't try to get a new lease. (I'm unsure if dhclient exited, or just failed to try a new discovery, but I think it actually exited).

I found this log snippet (that isn't very helpful, but it is from a time close to the dhcp servers coming back (around 10am) and from a host that failed to recover):

Nov 11 09:20:07 host dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 16
Nov 11 09:20:23 host dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 10
Nov 11 09:20:33 host dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
Nov 11 09:20:40 host dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8
Nov 11 09:20:48 host dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
Nov 11 09:20:55 host dhclient: No DHCPOFFERS received.

No further dhclient entries after that point, until it was started again after a reboot (no login possible, because LDAP server was inaccessible), over 3 hours later (our renewal time is 2 hours, expiry 4 hours or more).