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

How-to Configuration

Network Configuration

• Gateway: 10.0.0.1
• Domain: local

Primary Server

• IP Address: 10.0.0.12

Secondary Server

• IP Address: 10.0.0.11

First you must create a ddns key by running the following command:

ddns-confgen

• /etc/dhcpd.conf

# dhcpd.conf

ddns-update-style standard;     # The type of DDNS update to send (standard)
ddns-rev-domainname "in-addr.arpa."; # The Reverse domain name to update via DDNS
deny client-updates;            # Allow or Deny clients requesting DNS updates
do-forward-updates on;          # Enable DDNS updates
update-optimization on;         # Only update the DNS server when things change
update-conflict-detection on;   # Do multiple-client, one-name conflict detection
update-static-leases on;        # Send DDNS updates for static clients
use-host-decl-names on;         # Send DDNS updates only for the host part of a FQDN

include "/etc/dhcp/dhcpd-failover.conf";

subnet 10.0.0.0 netmask 255.255.255.0 {
        default-lease-time 86400;       # 1 day
        min-lease-time 43200;           # 12 hours
        max-lease-time 259200;          # 3 days
        option domain-name "local";     # The Network's Local Domain Name
        option routers 10.0.0.1;        # The Network's Default Gateway
        option ntp-servers 10.0.0.12;   # The Network's Network Time Servers
        option domain-name-servers 10.0.0.2, 10.0.0.12; # The Network's DNS Servers
        option broadcast-address 10.0.0.255;   # The Network's broadcast address
        option netbios-name-servers 10.0.0.12; # The Network's WINS Server

        pool {
                failover peer "Media";
                range 10.0.0.51 10.0.0.250;
        }
}

include "/etc/dhcp/dhcpd-static.conf";
include "/etc/dhcp/dhcpd-ddns.conf";

• /etc/dhcpd-failover.conf (on primary server)

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

failover peer "Media" {
        primary;
        address 10.0.0.12;
        peer address 10.0.0.11;
        max-response-delay 60;
        max-unacked-updates 10;
        mclt 900;
        split 128;
        load balance max seconds 3;
}

• /etc/dhcpd-ddns.conf (on primary server)

key "ddns-key" {
        algorithm hmac-sha256;
        secret "w4vOHY6roUCIB5Y/BwNrRkNQ2BF3jQNOs23Etfr5mD0=";
};

zone local. {              # name of your forward DNS zone
        primary 127.0.0.1; # DNS server IP address here
        secondary 10.0.0.11;
        key ddns-key;
}

zone 0.0.10.in-addr.arpa. {  # name of your reverse DNS zone
        primary 127.0.0.1;   # DNS server IP address here
        secondary 10.0.0.11;
        key ddns-key;
}