= DHCP Primary =

== Network ==

We will give the DHCP primary a static IP-address. Edit `/etc/networking/interfaces` and make the following changes.

{{{
# The primary network interface
#allow-hotplug eth0
#iface eth0 inet dhcp

auto eth0
iface eth0 inet static
        address 192.168.1.38
        network 192.168.1.0
        netmask 255.255.255.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
}}}

== Software ==
Before installing the DHCP server, make sure that you do not have other DHCP servers running on your network. It can cause hours of debugging.

 * Save time by running a static IP on the host you are configuring your system from, so you do not loose your ssh connections randomly.
 * Remember that switching off an existing DHCP server will cause all your devices to get new IP-adresses. Some devices may have to be rebooted to work properly again.
 * If you use the same IP-address range on both old and new DHCP server, then you may run into IP-address conflicts too.

Install the DHCP server.
{{{
apt-get install isc-dhcp-server
}}}

== Configure the server ==

=== Stop the server ===
{{{
service isc-dhcp-server stop
}}}

=== Get the DDNS update key ===

Copy your DDNS update key from the DNS Master and save it in `/etc/dhcp/ddns-update.kallenberg.dk`. Edit `/etc/dhcp/ddns-update.kallenberg.dk` and remove the quotations. If the quotations are not removed, then the DHCP server will not accept it as a valid key.
{{{
key ddns-update {
        algorithm hmac-sha512;
        secret yYFzfibvlpS33+vsngV2jF5tGkTiVSjhYoFuV0T7bnCVfFGx3Mu05SW+LakImdofkNM00LxHCLuvD1W1vSWMmA==;
};
}}}

=== Choose Network Device ===
Edit `/etc/default/isc-dhcp-server` and set the dhcp server to run on `eth0`.
{{{
INTERFACESv4="eth0"
}}}

=== Edit dhcpcd.conf ===
Comment out all lines in `/etc/dhcp/dhcpd.conf` and add the following to the bottom of the file:
{{{
include "/etc/dhcp/dhcpd.conf_default";
include "/etc/dhcp/ddns-update.kallenberg.dk";
include "/etc/dhcp/dhcpd.conf_primary";
include "/etc/dhcp/dhcpd.conf_subnet";
include "/etc/dhcp/dhcpd.conf_static";
}}}

=== Individual Config Files ===

==== Server ====
`/etc/dhcp/dhcpd.conf_default`
{{{
option domain-name "kallenberg.dk";
option domain-name-servers 192.168.1.36, 192.168.1.37;
default-lease-time 3600;
max-lease-time 7200;
log-facility local7;
update-optimization off;
}}}

==== Subnet ====
`/etc/dhcp/dhcpd.conf_subnet`
{{{
ddns-update-style standard;
ddns-updates on;
ddns-domainname "kallenberg.dk";
ignore client-updates;
update-static-leases on;

# forward zones for DNS updates
zone kallenberg.dk {
        primary 192.168.1.36;
        key ddns-update;
}

# reserse zone for DNS updates
zone 1.168.192.in-addr.arpa {
        primary 192.168.1.36;
        key ddns-update;
}

subnet 192.168.1.0 netmask 255.255.255.0 {

        pool {
                failover peer "network";
                range 192.168.1.96 192.168.1.127;
        }

        option routers 192.168.1.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 192.168.1.255;
        option domain-name "kallenberg.dk";
        option domain-name-servers 192.168.1.36, 192.168.1.37;
        option ntp-servers 192.168.1.40, 192.168.1.41;
        #option ntp-servers ntp01, ntp02;

        default-lease-time 3600;
        max-lease-time 7200;

}
}}}

==== Static IP-adresses ====

We would like servers to have static IP-adresses, but not more static than controlling it from the DHCP server. Remember to keep this file synchronized with the one on the DHCP secondary.

`/etc/dhcp/dhcpd.conf_static`
{{{
host ntp01 {
        hardware ethernet 52:54:00:9e:33:2f;
        fixed-address 192.168.1.40;
}

host ntp02 {
        hardware ethernet 52:54:00:c5:f1:92;
        fixed-address 192.168.1.41;
}
}}}

==== DHCP Primary ====
`/etc/dhcp/dhcpd.conf_primary`
{{{
failover peer "network" {
        primary;
        address 192.168.1.38;
        port 647;
        peer address 192.168.1.39;
        peer port 647;
        max-response-delay 60;
        max-unacked-updates 10;
        mclt 3600;
        split 128;
        load balance max seconds 3;
}
}}}

=== Start the server ===
{{{
service isc-dhcp-server start
}}}
Notice that even though the server is started, it will not begin to hand out IP-addresses yet. It will wait until it sees the secondary. Once it has seen the secondary, the DHCP server will begin to work.

== References ==

 * https://kb.isc.org/docs/aa-01091