How to configure for DHCP relay 1

[yizhar]

HI.

I want to configure a Cisco ver 12.2 router which is installed at a brance office, to act as DHCP relay (or proxy or helper - I don't know which is the Cisco term) and to forward DHCP packets to a DHCP server on the main office.

The connection to main office is leased line 256kbps.

The DHCP server address is 192.168.1.1
The router Ethernet address is 192.168.0.254
Therer are 2 additional routers in the path between the branch office router and the DHCP server.
There are no access lists in use.
I know that I need to create the scope 192.168.0.0 on the DHCP server, that's no problem for me. I'm looking only for the router configuration.

I have read some Cisco docs from the web site but still not sure what is the best and exact configuration to use.

Thanks for any tips and sample config.

Bye
Yizhar Hurwitz

http://come.to/yizhar

http://teachers.sivan.co.il/yizhar

 

[wybnormal]

IP helper is the easiest command to forward DHCP packets from a single server. The IP helper goes on the interface closest to the requesting client.

router(config-if)#IP helper-address 10.10.10.255

The client will broadcast looking for any DHCP server. The interface pcks up the broadcast and turns it into a unicast packet in order to route it back to whatever network you said in the command string. This can be a broadcast on the subnet of the server OR a directed broadcast OR a single IP address. The DHCP server will receive the broadcasted request and respond to it but the MAC will be the router. When the router receives the response, it strips and replaces the MAC and forwards it to the client who then thinks it's talking with the DHCP server directly.

I've glossed over a bit but I think there is enough here for the general idea.

Using One DHCP Server for Voice and Data Networks

http://www.cisco.com/warp/public/788/AVVID/dhcp-multintwk.html

Hope this helps

MikeS
Find me at

http://www.packetattack.com

"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu

 

[yizhar]

Thanks a lot.

It is working now, with the following config:

int e0
ip helper 192.168.1.1
exit
service dhcp

You really saved me some time - before this I was confused and tried some other commands with no success.

Bye
Yizhar Hurwitz

http://come.to/yizhar

http://teachers.sivan.co.il/yizhar