Ubuntu – dhcp server ‘not configured to listen on any interfaces’

bootdhcpinitscriptingUbuntu

I'm at my wits end on this one; I have tried for hours to get this to work, but I'm stumped. Hope one of you can help. 🙂

I'm trying to get dhcp3-server to work on Ubuntu. It's installed, and setup correctly to run in rc2,3,4,5.d runlevels. On boot, its init.d script does get run, and in syslog, I get the following:

Oct 18 20:40:37 jez-ubuntu dhcpd: Internet Systems Consortium DHCP Server V3.1.1
Oct 18 20:40:37 jez-ubuntu dhcpd: Copyright 2004-2008 Internet Systems Consortium.
Oct 18 20:40:37 jez-ubuntu dhcpd: All rights reserved.
Oct 18 20:40:37 jez-ubuntu dhcpd: For info, please visit http://www.isc.org/sw/dhcp/
Oct 18 20:40:37 jez-ubuntu dhcpd: Wrote 2 leases to leases file.
Oct 18 20:40:37 jez-ubuntu dhcpd:
Oct 18 20:40:37 jez-ubuntu dhcpd: No subnet declaration for eth1 (0.0.0.0).
Oct 18 20:40:37 jez-ubuntu dhcpd: ** Ignoring requests on eth1.  If this is not what
Oct 18 20:40:37 jez-ubuntu dhcpd:    you want, please write a subnet declaration
Oct 18 20:40:37 jez-ubuntu dhcpd:    in your dhcpd.conf file for the network segment
Oct 18 20:40:37 jez-ubuntu dhcpd:    to which interface eth1 is attached. **
Oct 18 20:40:37 jez-ubuntu dhcpd:
Oct 18 20:40:37 jez-ubuntu dhcpd:
Oct 18 20:40:37 jez-ubuntu dhcpd: Not configured to listen on any interfaces!
Oct 18 20:40:39 jez-ubuntu NetworkManager: <info>  (eth0): device state change: 1 -> 2
Oct 18 20:40:39 jez-ubuntu NetworkManager: <info>  (eth0): bringing up device.
Oct 18 20:40:39 jez-ubuntu NetworkManager: <info>  (eth0): preparing device.
[...]

As you can see, dhcpd appears to be running before NetworkManager, which is what sets up my eth0 (internet) and eth1 (home network) interfaces. You'd think this had something to do with the rcX.d symlink names, and that dhcpd was named to start before NetworkManager. Not so. My dhcp3-server symlinks are named 'S99dhcp3-server' and the Network Manager symlinks are named 'S50NetworkManager', so it should be starting before the dhcp server. In addition, if I actually run (as root) from the commandline '/etc/init.d/dhcp3-server'… the server runs OK! It only fails at boot!

Why does it say it's not configured to listen on any interfaces? Is the network manager not bringing interfaces eth0 and eth1 up until after all my boot scripts have run? If this is the case, what use is it? Surely other scripts would need these interfaces to be available at boot time? Here's my /etc/dhcp3/dhcpd.conf file:

subnet 192.168.0.0 netmask 255.255.255.0 {
        option routers 192.168.0.1;
        option subnet-mask 255.255.255.0;
        option domain-name-servers 87.194.0.51;
        option ip-forwarding off;
        range dynamic-bootp 192.168.0.100 192.168.0.254;
        default-lease-time 21600;
        max-lease-time 43200;
}

and my /etc/default/dhcp3-server file:

# Defaults for dhcp initscript
# sourced by /etc/init.d/dhcp
# installed at /etc/default/dhcp3-server by the maintainer scripts

#
# This is a POSIX shell fragment
#

# On what interfaces should the DHCP server (dhcpd) serve DHCP requests?
#       Separate multiple interfaces with spaces, e.g. "eth0 eth1".
INTERFACES="eth1"

As far as I can tell, these are all correct. Any ideas?

Best Answer

OK, I think i've fixed this issue. And it IS a bug in Linux's network manager.

See, the network manager runs as part of the boot process (that'd be the 'S50NetworkManager' symlink) and brings up your ethernet interfaces. However, it does it asynchronously. This means that the network manager returns immediately, implying to the scripts after it, "OK - network's been set up." Actually, it hasn't, and the network manager is sitting there in the background getting on with setting up the network. Meanwhile, the boot scripts after it are running with the assumption that the network interfaces will be available, which is a race condition, depending on whether the network manager has gotten round to setting them up yet.

This is a horrible situation and a bug I'm amazed hasn't been fixed. One way of getting round it is to ditch the network manager and instead set up your interfaces by editing /etc/network/interfaces. Rather than do that work, though, I tried the ugly hack suggested in this bug report: https://bugzilla.redhat.com/show_bug.cgi?id=486372

I added a 5 second delay ('sleep 5') into the beginning of the start function in dhcp3-server's init.d script, this giving the network manager ample time to get the network interfaces set up (although of course there is still no guarantee) - and it worked. Now, dhcpd succeeds on startup.

As detailed in bugs #486372 and #447442 on bugzilla.redhat.com, this is either a bug with network manager (it should block until its wired network interfaces are available), or with dhcpd (it should be updated to wait for network interfaces to become available, rather than just crashing out). It is definitely a bug of sorts, though.

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