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Failover Dynamic DNS (BIND and DHCP)
Setup the master DNS
Setup the DHCP slave
Setup DNS slave
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If a machine uses a dynamic ip-address retrieved from a DHCP server the ip-address will not resolve to it's domainname. Usually we setup DNS with static ip-addresses. However we can setup a dynamic DNS server with DHCP so every machine which retrieves its ip-address from the DHCP server will be registered or updated in the DNS. In this tutorial I will setup a failover. We need to install some packages if they are not allready installed:

yum install ntp dhcp bind bind-chroot bind-libs bind-utils

Let's asume the domainname is mydomain.com, the network is 192.168.1/0/24, Gateway 192.168.1.254, the DHCP servers and DNS servers are 192.168.1.2 and 192.168.1.4.

For a failover DHCP setup both servers should have the time in sync. Therefore we create a simple cron-job on both servers to sync the time every day with a time-server. Create the file /etc/cron.daily/timesync and add the lines

#!/bin/bash
/usr/sbin/ntpdate ntp.xs4all.nl

On the master server (192.168.1.2) edit /etc/dhcpd.conf

authoritative;
option domain-name "mydomain.com";
option domain-name-servers 192.168.1.2,192.168.1.4;
option netbios-name-servers 192.168.1.2;
ddns-update-style interim;
ddns-updates on;
ddns-domainname "mydomain.com";

key rndckey {
  algorithm       hmac-md5;  
  secret          "your key from /etc/rndc.key";
}

zone mydomain.com
{
  primary 127.0.0.1;
  key rndckey;
}

zone 1.168.192.in-addr.arpa
{
  primary 127.0.0.1;
  key rndckey;
}

failover peer "failover" {
  primary;
  address 192.168.1.2;
  port 647;
  peer address 192.168.1.4;
  peer port 647;
  max-response-delay 60;
  max-unacked-updates 10;
  mclt 3600;
  split 128;
  load balance max seconds 3;
}
subnet 192.168.1.0 netmask 255.255.255.0
{
  pool {
    failover peer "failover";
    range 192.168.1.20 192.168.1.60;
    option dhcp-server-identifier 192.168.1.2;
    option domain-name-servers 192.168.1.2;
    option subnet-mask 255.255.255.0;
    option broadcast-address 192.168.1.255;

    default-lease-time 43200;
    max-lease-time 43200;
    option domain-name "mydomain.com";
    option routers 192.168.1.254;
    deny dynamic bootp clients;
    }
  allow unknown-clients;
  ignore client-updates;
}