Cisco Router DHCP Configuration

[kjanakiraman]

Hi,

We have a Cisco 3640 router with version 12.3(1a). I have two Ethernet interface in the Router E1/0 and E1/1. NATing is enabled on both the interface. E1/0 is the outside interface and E1/1 is the inside interface. I configured DHCP like the one below

ip dhcp excluded-address 192.168.25.1

!

ip dhcp pool Test

network 192.168.25.0 255.255.255.0

default-router 192.168.25.1

dns-server 192.168.25.3

lease infinite

When i try getting ip address for my system from the router. The Router is not leasing out ip address to the system.

Can someone advice me how should i proceed to make the cisco router as dhcp server.

Thanks in Advance

[sachinraja]

Try changing the lease in the dhcp configuration.

Router(config-dhcp)#lease {days [hours][minutes] | infinite}

Router will release the IP within the duration specified in this command.

Cheers !!

[rjackson]

You need to exclude the DNS server's address too. Is the pc on the router interface with the 25.1 address?

[thisisshanky]

Have you configured 192.168.25.1 ip address on E1/1 ?? Only then it will lease an ip from the DHCP pool Test on that interface. Also check to see if your PC has been configured to "obtain an IP address automatically". Use command prompt to see the ip address using "ipconfig" or "ipconfig /all". Use "ipconfig /renew" to renew your ip address.

You should exclude 192.168.25.3, so that the router does not assign that ip address to any PC.

The way you have configured should work normally, with 192.168.25.2 (the first ip address that can be assigned in the pool) being the ip address assigned to the PC (mostly all DHCP servers assign starting with the first available address).

[kjanakiraman]

Thanks a lot for all your mails. I have kept the lease time to infinite and i will change it to hours. E1/1 is the inside interface which has 192.168.25.1. The PC is configured for "obtain ip address automatically" and i could not renew the ip address. I removed the dns-server ip address also. The PC is in the same interface. But still i am not getting ip address from the Router.

Thanks in advance

[thisisshanky]

Have you tried the same with a different PC ? (Just to eliminate issues with the TCP/IP stack of the PC)....FYI...98percent Microsoft issues are resolved by restarting the PC once...LOL.

[kjanakiraman]

Hi,

Thanks a lot for your mail. I tried with two different PC and both are having the same problem. Is there any restrictions on the Ethernet interface. I had configured for cisco 3640 router before which had fast ethernet interface and it worked fine.

Thanks in Advance

[pfalk]

This should work. To debug, try:

debug ip dhcp server packet

and look at the packets.

I've found that dhcp sometimes fails without a good error message when there are conflicts, such as when the dhcp pool contains an IP address that is already "taken" by one of the router's interfaces. Check to see if there are any such issues with your config.

Peter