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IP dhcp excluded-address

Command

IP dhcp excluded-address

Use

This command prevents IP addresses from being assigned by the router’s DHCP server. This is used to prevent IP conflicts with statically assigned servers and routers.

Syntax

Router(config)#ip dhcp excluded-address <low IP> <high IP>

Example

simple

In the below example we will configure R2 to provide DHCP services for R1, but we will ensure that nothing under 10.1.1.100 will be assigned.
First we configure the DHCP server with ip dhcp pool and exclude the ip addresses.

R2(config)#ip dhcp pool R1_Pool
R2(dhcp-config)#network 10.1.1.0 /24
R2(dhcp-config)#dns-server 4.2.2.2
R2(dhcp-config)#default-router 10.4.4.1
R2(dhcp-config)#exit
R2(config)#ip dhcp excluded-address 10.1.1.1 10.1.1.99

Currently R1’s Fa0/0 does not have an IP address

R1(config-if)#do show ip interface brief | ex unass
Interface IP-Address OK? Method Status Protocol
Serial1/0 10.4.4.1 YES manual up up
Loopback0 10.0.0.1 YES manual up up

After we configure ip address dhcp on R1’s Fa0/0, it receives an IP address of 10.1.1.1

R1(config)#int fa0/0
R1(config-if)#ip address dhcp
R1(config-if)#
*Mar 1 00:40:36.339: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.1.2 (FastEthernet0/0) is down: address changed

R1(config-if)#
*Mar 1 00:56:44.903: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0 assigned DHCP address 10.1.1.100, mask 255.255.255.0, hostname R1

R1(config-if)#
*Mar 1 00:41:21.567: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.1.2 (FastEthernet0/0) is up: new adjacency
R1(config-if)#
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