For enabling DHCP service in your cisco router, first go in to the interface in which you need to provide DHCP Service and provide an IP address for the same if it doesnt have. This IP will be the gateway ip address. I am providing 10.xx.xx.xx ip range here
Router(config)# interface ethernet0/0
Router(config-if)#ip address 10.0.0.1 255.0.0.0
Router(config-if)#no shutdown
Now we need to enable DHCP service, for that first we need to give a ip pool name. Name can be anything like pool1, or yournamepool etc.
Router(config)# ip dhcp pool pool1
Now it will enter DHCP-Config, specify the network range and subnet for DHCP service. Ip would be given from this range and according to subnet mask. I am assuming , at this point you already know subnetting and related stuff.
Router(dhcp-config)# network 10.0.0.0 255.255.255.0
Now specify the default-router, that is the gateway ip address. We did that in first step. In this case it is 10.0.0.1
Router(dhcp-config)#default-router 10.0.0.1
Now you can exit DHCP configuration by
Router(dhcp-config)#exit
In case, if you need to exclude a range of ip from DHCP pool you can give it in the following step. Say you need to skip like 10.0.0.200–10.0.0.240
Router(config)#ip dhcp excluded-address 10.0.0.200 10.0.0.240
Now all the machines connected to that particular port via a switch will get IP allocation using DHCP protocol. In case you already have machines running, you can give ipconfig/renew to get a new ip. Or just restart machine, or even change static ip assigning to DHCP.
Hope this helps.
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