Cisco IOS Cookbook, 2nd Edition

DHCP Static Mapping

Problem

You want to enable the assignment of static IP addresses from a text file.

Solution

To enable the assignment of static IP addresses from a text file, first you must create a static DHCP mapping file on your TFTP server:

Freebsd% cat /tftpboot/dhcp.static 
*time* Aug 17 2006 03:52 PM

*version* 2

!IP address       Type      Hardware address               Lease expiration

10.1.1.16 /24    id        0100.104b.33da.74                Infinite
10.1.1.17 /24    id        0100.0dbc.eff6.38                Infinite
10.1.1.18 /24    id        0100.0a5e.4001.27                Infinite
10.1.1.19 /24    id        0100.0331.327e.41                Infinite
10.1.1.20 /24    id        0100.0d60.b21a.4c                Infinite 

*end*
Freebsd%

To enable the router to read the static text file from the TFTP server, use the origin file command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip dhcp pool OREILLY
Router1(dhcp-config)#origin file tftp://172.25.1.1/dhcp.static
Router1(dhcp-config)#default-router 10.1.1.1 
Router1(dhcp-config)#dns-server 172.25.1.1 172.25.1.3 
Router1(dhcp-config)#domain-name oreilly.com
Router1(dhcp-config)#lease 3
Router1(dhcp-config)#end
Router1#

Discussion

As demonstrated in Recipe 20.7, we can statically bind IP addresses to hardware addresses; however, doing so requires a dedicated DHCP pool, and more importantly, many lines of configuration. For instance, the following is a sample configuration for a single statically mapped IP address:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip ...