dhclient receives no DHCPOFFERS, but will inherit Windows lease

[Alan De Smet <chaos highprogrammer com>]

In short, sometimes dhclient will complain "No DHCPOFFERS
received."  Tinkering with the interface doesn't appear to help,
but booting into Windows XP (which successfully gets an address
from DHCP), then back into Linux makes it work.

The dhclient in question is Red Hat's "dhclient-3.0pl1-23" from
Red Hat 9.  I experienced similar behavior with Red Hat 7.3 (I
believe using dhcpcd, but I didn't investigate very closely.  And
I was running Windows 98 which "made it work" instead of XP.).
I'm on Charter Pipeline cable modem server in the Madison,
Wisconsin area (who knows, it may be a regional server
configuration thing).

When the DHCP attempt fails I've tried cycling the network
("service network restart", "ifup eth1") and more extreme
measures (shutting down the computer, unplugging the cable modem
(there is no switch), plugging in the cable modem, powering back
up the computer into Linux). These attempts don't appear to fix
anything.

A typical failure case (from /var/log/messages):

Sep  3 22:07:27 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 4
Sep  3 22:07:31 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 7
Sep  3 22:07:38 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 14
Sep  3 22:07:52 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 7
Sep  3 22:07:59 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 19
Sep  3 22:08:18 localhost dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 10
Sep  3 22:08:28 localhost dhclient: No DHCPOFFERS received.

Not much to see there.

More interesting are the cases where it does work.  Bear in mind
that this is the first and last message from dhclient after
booting up.  This is after booting Windows XP, then rebooting
back into Linux:

Sep  3 22:14:25 localhost dhclient: DHCPOFFER from XXX.XXX.XXX.XXX

(Where XXX.XXX.XXX.XXX is is some external address.  Since I'm
not sure what it is (it might be my cable modem), I'm a bit leary
of publically broadcasting it.)

Notably missing is even a single DHCPDISCOVER attempt.  Maybe
dhclient is suppressing any messages until it thinks there might
be a problem, but that would surprise me.  I would have expected
a DHCPDISCOVER before getting any DHCPOFFERs.

Sometimes the DHCPOFFER appears just before the DHCPREQUEST, on
the same line.  Again, this is immediately after startup.  It
looks like some sort of output error causing two writes to
overlap:

Aug 16 13:01:07 localhost dhclient: DHCPOFFER from XXX.XXX.XXX.XXX <30>Aug 16 13:01:07 dhclient: DHCPREQUEST on eth1 to 255.255.255.255 port 67

On at least a few occasions instead of DHCPOFFER I'll get DHCPACK
after boot up.  This appears to occur when I restart the system
after already getting a DHCPOFFER.  It might just be expected
behavior when dhclient attempts to update the lease it already
knew about just a few minutes before.

This behavior appears consistant over the last month (thats as
far as my logs go).  The user observable behavior certainly
matches for well over a year (under Red Hat 9 now, and 7.3
prior).

I'm not sure what to make of the machine making the offer
(XXX.XXX.XXX.XXX in the above.  It's always the same IP address).
Reverse DNS fails to turn up anything.  traceroutes to the
machine are a bit random (sometimes the first hit, sometimes the
third, fifth, or never).  traceroutes to external machines work
fine, but the unknown DHCP providing machine is always the first
hop to respond.  Poking around it doesn't appear to be my cable
modem (which responds internally with a 192.168. address, and if
I'm reading the cable modem's web configuration screen correctly,
is using a different address (but it shares the first 2 bytes of
the address with the mysterious DHCP server).

Googling the web and usenet isn't turning much up.  It looks like
most people have the opposite problem (after rebooting from
Windows, dhclient can't get an IP).  I ran into some passing
references to dhclient having problems if the DHCP server is too
many hops away, but I'm not finding concrete details.  It seem
irrelevant given that my DHCP server is apparently somewhere
nearby.


This has been bugging me for a while, and I'm not sure how to
proceed.  Booting into Windows briefly is such a crude
workaround.  Can anyone offer any advice or suggestions on what
to investigate?

-- 
Alan De Smet