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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?

Jez
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8 Answers8

4

you can modify your /etc/network/interfaces like this:

iface eth1 inet static
  address 192.168.50.1
  netmask 255.255.255.0
  up service dhcp3-server restart

so dhcp3-server will be (re)started after network interface (eth1) has been really up.

4

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.

Jez
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1

following is a list of points to verify if you are having a subject error:

  1. isc-dhcpd-server is looking inside:

/etc/default/isc-dhcp-server

file to identify interface name the ONLY will be serving dynamic addresses (it's no longer ALL interfaces of your system but only mentioned in this file). be sure you have at least 1 interface defined (and it's not necessary could be eth0 anymore):

INTERFACES="enp0s31f6"
  1. isc-dhcpd-server will not accept mentioned above interface (enp0s31f6 in my example) to serve dynamically allocated IP addresses over it if you didn't assigned static IP address to the one. the address assignment is done in:

/etc/network/interfaces

by providing following block of settings:

# Define the static address and set it to serve with DHCP.  Link it to the existing interface.
iface enp0s31f6 inet static
address 10.20.0.1
netmask 255.255.255.240
#below are optional settings
#gateway 192.168.100.251
#dns-nameservers 8.8.8.8

after configuring static address for the selected interface make sure it is available, up and defined address is assigned (by restarting networking) with the help of the following command:

sudo service networking restart

otherwise isc-dhcpd-server will refuse to run

  1. isc-dhcpd-server will serve only interfaces having dynamic releasing subnetwork defined in

/etc/dhcp/dhcpd.conf

by providing separate block definition (at least one) for the interface address (your selected interface static IP must match configured subnet):

subnet 10.20.0.0 netmask 255.255.255.0 {
    range 10.20.0.10 10.20.0.100;
    option subnet-mask 255.255.255.0;
    option routers 10.20.0.1;
    option broadcast-address 10.20.0.255;
    option domain-name-servers 192.168.100.254, 8.8.8.8;
}

by only conforming all 3 rules you'll get DHCP service working on your Ubuntu (resolved and verified on version 16.04)

finally it's now a time to start isc-dhcpd-server by executing command:

sudo service isc-dhcp-server start

to verify configuration success, use another command:

sudo service isc-dhcp-server status

and look into following lines for the confirmation of success:

● isc-dhcp-server.service - ISC DHCP IPv4 server
Active: active (running) since Wed 2017-05-10 15:28:13 CEST; 29min ago
May 10 15:28:13 system-P50 dhcpd[26869]: Listening on LPF/enp0s31f6/0a:3e:47:75:17:a8/10.20.0.0/24
Oleg Kokorin
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1

I meet the error, such as "No subnet declaration for eth1" and "Not configured to listen on any interfaces!".

Then I add the eth1 subnet declaration in the dhcpd.conf although the subnet not lease the address. And it work.

subnet 10.32.64.0 netmask 255.255.252.0 {
    option routers 10.32.64.1;
}
VictorLee
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0

I was having this issue for a different reason, I think.

I was trying to use DHCP to configure the interface the server would listen on. AKA my LAN was connected to the eth0 port of the server, and I was trying to get DHCP to configure eth0. Doesn't work, apparently; DHCP listening interfaces have to be configured statically (/etc/network/interfaces).

Correct me if I'm wrong. I didn't think one should have to statically configure a DHCP listening device.

Luke has no name
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I had a similar problem, but in my case the network interface (eth0) was never up - it had failed to initialise properly. This was happening intermittently however, approx 20% of the time. Putting in a delay, or restarting the dhcp server as suggested in other answers did not solve my problem.

In my case the solution was to restart both the network services and then the dhcp server via something like the following script (fragments only, not runnable start to end)...

# Check if the networking is running ...
# look for "192.168.0.202" within this command's output
ifconfig

# If the networking is not running, then restart the network interfaces via this command:
sudo service networking restart

# Check if the DHCP service is running ...
# look for "dhcpd" within this command's output
ps -C dhcpd

# If the DHCP service is not running, then restart the DHCP service via this command:
sudo service isc-dhcp-server restart
dodgy_coder
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I just ran into this issue on Ubuntu, and I fixed it a little differently. I am using the isc-dhcp-server service but it was attempting to start before the required interface was up, crashing, and then exhausting the respawn limit. I made a small edit to the start on line in the upstart config file in /etc/init:

start on runlevel [2345] and net-device-up IFACE=eth0

This way the service will not attempt to start until the required interface is up.

Smurph269
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I have fighted whith this error message for 1 day. 

No subnet declaration for eth1 (no IPv4 addresses).

Finaly the error in my case comes from dhcp service script by starting it with systemctl commands.

#cat /etc/systemd/system/dhcpd.service

[Service]
Type=notify
ExecStart=/usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --no-pid **eth1**

Just modify the ethXX number

Reload

#systemctl daemon-reload

relaunch it:

#systemctl start dhcpd
Zlatco
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