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DHCP Static Mapping

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#

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 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)#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)#end
Router1#

While this method of assigning static IP addresses is useful for sites with a few required static addresses, it doesn't scale well when you need to assign a large number of them. Building a new DHCP pool per static address not only consumes NVRAM space, but also clutters the router configuration file.

Beginning with IOS Version 12.3(11)T, Cisco supports the ability to assign static IP address via text files. To begin, you must first create the static mapping text file on your TFTP server. There is no limit to the number of static entries you can add to the file; however, the file must follow a certain format. The following is an example text file:

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&n

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