Dynamic Host Configuration Protocol (DHCP)
The Dynamic Host Configuration Protocol (DHCP) is a network service that enables host computers to be automatically assigned settings from a server as opposed to manually configuring each network host. Computers configured to be DHCP clients have no control over the settings they receive from the DHCP server, and the configuration is transparent to the computer's user.
note: this package was called dhcp3-server in versions prior to precise 12.04 LTS.
Installation
At a terminal prompt, enter the following command to install dhcpd:
sudo apt-get install isc-dhcp-server
You will probably need to change the default configuration by editing /etc/dhcp3/dhcpd.conf to suit your needs and particular configuration.
You also need to edit /etc/default/isc-dhcp-server to specify the interfaces dhcpd should listen to. By default it listens to eth0.
Also, you have to assign a static ip to the interface that you will use for dhcp. If you will use eth0 for providing addresses in the 192.168.1.x subnet then you should assign for instance ip 192.168.1.1 to the eth0 interface using NetworkManager. Without this step you will get an error from dhcpd when starting the service.
Configuration
The error message the installation ends with might be a little confusing, but the following steps will help you configure the service:
Most commonly, what you want to do is assign an IP address randomly. This can be done with settings as follows:
nano -w /etc/dhcp/dhcpd.conf
# Sample /etc/dhcpd.conf
# (add your comments here)
default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-name "mydomain.example";
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.10 192.168.1.100;
range 192.168.1.150 192.168.1.200;
} This will result in the DHCP server giving a client an IP address from the range 192.168.1.10-192.168.1.100 or 192.168.1.150-192.168.1.200. It will lease an IP address for 600 seconds if the client doesn't ask for a specific time frame. Otherwise the maximum (allowed) lease will be 7200 seconds. The server will also "advise" the client that it should use 255.255.255.0 as its subnet mask, 192.168.1.255 as its broadcast address, 192.168.1.254 as the router/gateway and 192.168.1.1 and 192.168.1.2 as its DNS servers.
If you need to specify a WINS server for your Windows clients, you will need to include the netbios-name-servers option, e.g.
nano -w /etc/dhcp/dhcpd.conf
option netbios-name-servers 192.168.1.1;
Start and stop service
sudo service isc-dhcp-server restart sudo service isc-dhcp-server start sudo service isc-dhcp-server stop
dhcp3-server and multiple interfaces
multiple interfaces example
Interface
nano -w /etc/network/interfaces
auto lo
iface lo inet loopback
mapping hotplug
script grep
map eth1
iface eth1 inet dhcp
auto eth0
iface eth0 inet static
address 10.152.187.1
netmask 255.255.255.0
auto wlan0
iface wlan0 inet static
address 192.168.1.1
netmask 255.255.255.0
up /sbin/iwconfig wlan0 mode TTTTTT && /sbin/iwconfig wlan0 enc
restricted && /sbin/iwconfig wlan0 key [Y] XXXXXXXX && /sbin/iwconfig
wlan0 essid SSSSSSSS
auto eth1
Select Interface card
nano -w /etc/default/isc-dhcp-server
INTERFACES="wlan0 eth0"
Configure Subnet
nano -w /etc/dhcp3/dhcpd.conf
ddns-update-style none;
log-facility local7;
subnet 192.168.1.0 netmask 255.255.255.0 {
option routers 192.168.1.1;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option domain-name-servers 194.168.4.100;
option ntp-servers 192.168.1.1;
option netbios-name-servers 192.168.1.1;
option netbios-node-type 2;
default-lease-time 86400;
max-lease-time 86400;
host bla1 {
hardware ethernet DD:GH:DF:E5:F7:D7;
fixed-address 192.168.1.2;
}
host bla2 {
hardware ethernet 00:JJ:YU:38:AC:45;
fixed-address 192.168.1.20;
}
}
subnet 10.152.187.0 netmask 255.255.255.0 {
option routers 10.152.187.1;
option subnet-mask 255.255.255.0;
option broadcast-address 10.152.187.255;
option domain-name-servers 194.168.4.100;
option ntp-servers 10.152.187.1;
option netbios-name-servers 10.152.187.1;
option netbios-node-type 2;
default-lease-time 86400;
max-lease-time 86400;
host bla3 {
hardware ethernet 00:KK:HD:66:55:9B;
fixed-address 10.152.187.2;
}
}
Check Route
ip route
192.168.1.0/24 dev wlan0 scope link 82.16.TT.0/24 dev eth1 scope link 10.152.187.0/24 dev eth0 scope link default via 82.16.TT.UU dev eth1
Permission issues with ISC-DHCP server
Sometimes upon rising DHCP server informs about permission errors like
Can't open /etc/dhcp/dhcp.conf: permission denied
or
Can't open /var/lib/dhcp/dhcpd.leases: permission denied.
If after checking the permissions are found to be correct, check apparmor profile for dhcpd:
shell# sudo apparmor_status apparmor module is loaded. 15 profiles are loaded. 15 profiles are in enforce mode. /sbin/dhclient /usr/bin/evince /usr/bin/evince-previewer /usr/bin/evince-thumbnailer /usr/lib/NetworkManager/nm-dhcp-client.action /usr/lib/connman/scripts/dhclient-script /usr/lib/cups/backend/cups-pdf /usr/lib/telepathy/mission-control-5 /usr/lib/telepathy/telepathy-* /usr/sbin/cupsd /usr/sbin/dhcpd /usr/sbin/mysqld-akonadi /usr/sbin/mysqld-akonadi///usr/sbin/mysqld /usr/sbin/tcpdump /usr/share/gdm/guest-session/Xsession 0 profiles are in complain mode. 4 processes have profiles defined. 4 processes are in enforce mode. /sbin/dhclient (1092) /sbin/dhclient (1093) /usr/sbin/cupsd (978) /usr/sbin/mysqld-akonadi///usr/sbin/mysqld (2136) 0 processes are in complain mode. 0 processes are unconfined but have a profile defined.
If /usr/sbin/dhcpd is in the list of profiles do the following:
- 1.Stop apparmor deamon
sudo /etc/init.d/apparmor stop
- 2.Edit /etc/apparmor.d/usr.sbin.dhcpd with root permissions and ensure that file has following lines:
/var/lib/dhcp/dhcpd.leases* rwl, /var/lib/dhcp/dhcpd6.leases* rwl, /etc/dhcp/dhcpd.conf r, /etc/dhcp/dhcpd6.conf r,
- /var/lib/dhcp/dhcpd6.leases and /etc/dhcp/dhcpd6.conf are needed to run DHCP server in IPV6 mode, for example:
dhcpd -6 -cf /etc/dhcp/dhcpd6.conf -lf /var/lib/dhcp/dhcpd6.leases eth0
- 3.Start apparmor deamon
sudo /etc/init.d/apparmor start
After this operation apparmor deamon will allow dhcp server to open /etc/dhcp/dhcpd.conf or /var/lib/dhcp/dhcpd.leases files. For more information see man apparmor