Sending DHCP requests .... timed out

[Thomas Lange]

>>>>> On Sun, 03 Dec 2006 14:55:27 +0100, Ingo Wichmann <iw at linuxhotel.de> said:

    > * the install-client boots and gets a pxelinux bootprompt
    > * kernel loads

    > Then the kernel prints out:

    >   Sending DHCP requests ..... timed out!

    > But no packets are sent, i've checked this with tcpdump.
    > After a while the kernel tries again ( and again, and ... ):
Are you using a Cisco switch? I had similar problems with Cisco
switches when not enabling the fastport feature (this disables
spanning tree).

I guess it's the following problem. The kernel activates the
interface. Then the switch needs some time (too long) for doing the
spaning tree operation for a loop free topology for any bridged LAN.
It seems that the switch need too much time for this. During this time
the kernel sends several DHCP packets but they are not forwarded by
the switch because the spanning tree in not yet finished. If the
kernel send a numer of DHCP packages (for example) without success, it
reopens the network devices which triggers another spanning tree
detection on the switch.

Solution: Try another switch, which is faster in detecting the loop
free topology. Or have a look at the kernel source in
net/ipv4/ipconfig.c, where the parameters for the number of retries
and timeout parameter for reoping the network devices are definded.

-- 
regards Thomas