How-TO: Configure DHCP on a CISCO router

This post is about configuring a CISCO router to act as a DHCP server in your network.

Task1: Configure R1 to act as a DHCP server and provide all network information to hosts in the LAN dynamically. (R1 and R2 are directly connected via Ethernet)

Server Configuration (R1)

!-- enable dhcp server (default)

service dhcp

! -- defining DHCP pool with all network information

ip dhcp pool OFFICE
network 192.168.12.0 255.255.255.0
domain-name networkers-online.com
default-router 192.168.12.1 !-- gateway address
dns-server 192.168.12.100 192.168.12.101 !-- DNS servers
netbios-name-server 192.168.12.99 !-- WINS servers
lease 2 !-- lease time

!-- defining static binding to R2 using its client-id

ip dhcp pool STATIC
host 192.168.12.2 255.255.255.0
client-identifier 01cc.010d.f000.00

!-- exclude server and static addresses from the dynamic pool

ip dhcp excluded-address 192.168.12.1
ip dhcp excluded-address 192.168.12.100 192.168.12.101
ip dhcp excluded-address 192.168.12.200
p dhcp excluded-address 192.168.12.2

Client Configuration:

interface FastEthernet0/0
ip address dhcp client-id FastEthernet0/0

Troubleshooting and verfication:

IP address is assigned dynamically to R2

!-- R2 f0/0 address is assigned via DHCP

R2(config-if)#do sh ip int b
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.12.2 YES DHCP up up

!-- R1 bindings has R2 as a static entry

R1#sh ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address/
User name
192.168.12.2 01cc.010d.f000.00 Infinite Manual

R2 gets its domain-name dynamically from R1

R2#sh ip domain
networkers-online.com

R2 sets R1 as a default gateway using a floating static route

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static routeGateway of last resort is 192.168.12.1 to network 0.0.0.0

C 192.168.12.0/24 is directly connected, FastEthernet0/0
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
S* 0.0.0.0/0 [254/0] via 192.168.12.1

R2 learns Primary and secondary DNS servers from R1

R2#ping xyz.comTranslating "yahoo.com"...domain server (192.168.12.100) (192.168.12.101)
% Unrecognized host or address, or protocol not running.

for more information on how to configure DHCP features consult the following link CISCO IOS DHCP Server

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