isc-dhcp-server


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:

apt-get install isc-dhcp-server

You will probably need to change the default configuration by editing
/etc/dhcp/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:

vi -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.

vi -w /etc/dhcp/dhcpd.conf

option netbios-name-servers 192.168.1.1;

Start and stop service

service isc-dhcp-server restart
service isc-dhcp-server start
service isc-dhcp-server stop


dhcp-server and multiple interfaces



multiple interfaces example


Interface

vi -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

vi -w /etc/default/isc-dhcp-server

INTERFACES="wlan0 eth0"


Configure Subnet


vi -w /etc/dhcp/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:

Stop apparmor deamon
/etc/init.d/apparmor stop

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

Start apparmor deamon 
/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