Cisco IOS Cookbook, 2nd Edition

Allocating Static IP Addresses with DHCP

Problem

You want to ensure that your router assigns the same IP address to a particular device every time it connects.

Solution

The following commands ensure that the router assigns the same IP address to a device each time it requests one:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip dhcp pool IAN
Router1(dhcp-config)#host 172.25.1.33 255.255.255.0
Router1(dhcp-config)#client-identifier 0100.0103.85e9.87
Router1(dhcp-config)#client-name win2k
Router1(dhcp-config)#default-router 172.25.1.1 
Router1(dhcp-config)#domain-name oreilly.com
Router1(dhcp-config)#dns-server 172.25.1.1 
Router1(dhcp-config)#exit
Router1(config)#end
Router1#

Discussion

The router allows you to statically bind an IP address to a MAC address to ensure that a particular device always receives the same IP address. This is particularly useful for devices such as servers that must be available for access via a well-known IP address or DNS entry. Any device that accepts inbound sessions will probably require a static address. Being able to allocate these addresses via DHCP provides network administrator with greater control.

The configuration for a static DHCP mapping is slightly different than a dynamic pool. In particular, you must assign a separate dhcp pool for each static server. In our example, we created a pool named IAN to allocate a static IP address to user Ian. Also, instead of defining a network range of IP ...