ISC DHCP

This page explains how to install and use the ISC DHCP server.

• Also See: DHCP and BOOTP Parameters & DNSMasq

Installing the ISC DHCP Server

First you need to install the dhcp server

yum -y install dhcp

Basic DHCP Server Configuration

This is a vary basic configuration. The below configuration will allow 20 hosts to connect via the 192.168.1.0 network. They will receive a example.com hostname and be confiured to use the 192.168.1.1 gateway and nameserver(DNS).

• /etc/dhcpd.conf

allow bootp;
allow booting;
default-lease-time 1080000;  # The wait time before a client will start to renew, in seconds
max-lease-time 288000000;    # The Maximum time a client can keep it's IP before it MUST renew, in seconds
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.1;  # This is your clients default gateway
option domain-name-servers 192.168.1.1;   # This is your clients DNS server
option domain-name "example.com";   # This is your clients domain name
ddns-update-style ad-hoc;
option ip-forwarding off;
option nntp-server time.nist.gov;

subnet 192.168.1.0 netmask 255.255.255.0 {
   range 192.168.1.50 192.168.1.30;
}

# And here is the standard static IP system setup
host Samantha {
   hardware ethernet 00:b0:d0:db:02:bd;
   fixed-address 192.168.1.2;
}

Now lets make sure the dhcp demon is setup to auto start

/sbin/chkconfig dhcpd on

and to confirm it will start

/sbin/chkconfig --list dhcpd

If it is setup to start at boot you will see something like this:

dhcpd           0:off   1:off   2:on    3:on    4:on    5:on    6:off

And Start it

/sbin/service dhcpd start

Advanced DHCP Server Configuration

dnssec-keygen -a HMAC-MD5 -b 128 -n HOST dnskey

• /etc/dhcpd.conf

option time-servers 192.168.1.1;
allow bootp;
allow booting;
allow client-updates;
ddns-update-style interim;
ddns-updates on;
allow unknown-clients;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option domain-name-servers 192.168.1.2, 192.168.1.1;
option ip-forwarding off;
option nntp-server time.nist.gov;
option netbios-name-servers 192.168.1.3;

# Local DDNS Zone 
key dnskey {
	algorithm hmac-md5;
	secret "asiomasdfeCEDDo1JTt8Q==";
	};

# Zone Entry for example.com
zone example.com. {
	primary 192.168.1.1;
	key dnskey;
	}

# Zone Entry for wireless.example.com
zone wireless.example.com. {
	primary 192.168.2.1;
	key dnskey;
	}

# Local Area Network
zone 1.168.192.in-addr.arpa. {
	primary 192.168.1.1;
	key dnskey;
	}

# Wireless Network
zone 2.168.192.in-addr.arpa. {
	primary 192.168.1.1;
	key dnskey;
	}

subnet 192.168.1.0 netmask 255.255.255.0 {
	authoritative;
	allow client-updates;
	allow unknown-clients;
	option domain-name "example.com";
	option routers 192.168.1.1;
	pool {
		ddns-updates on;
		range 192.168.1.50 192.168.1.254;
		}
	}

subnet 192.168.2.0 netmask 255.255.255.0 {
	authoritative;
	allow client-updates;
	allow unknown-clients;
	option domain-name "wireless.example.com";
	option routers 192.168.2.1;
	option domain-name-servers 192.168.2.1;
	pool {
		ddns-updates on;
		range 192.168.2.2 192.168.2.254;
		}
	}

host computer1 {
	hardware ethernet 00:16:76:28:08:99;
	fixed-address 192.168.1.3;
}

host computer2 {
	ddns-hostname "computer2";
	hardware ethernet 00:0f:cb:9f:f5:ca;
	fixed-address 192.168.2.4;
}