How To Enable DHCP Across Subnets

[byrne1]

I am new to DHCP and I do not know how to enable this feature across subnets in my network.

My DHCP server is running Windows Server 2003 and is connected to a router w/ IP address of, let's say 1.1.1.1. The clients that I have set up for DHCP w/n the scope of this router work fine. I have three other locations w/ router IPs of 1.1.2.1, 1.1.3.1, and 1.1.4.1.

When I try to enable DHCP on a client XP machine in the 1.1.2.1 subnet it does not work. When the client is turned on the IP address is essentially set to 0.0.0.0. When I issue the command "ipconfig /renew" at the command prompt the machine hangs (at least the command prompt hangs w/ a blinking cursor).

Can someone please offer me some assistance with this issue? Thank you in advance for any help you may be able to provide.

 

[ProfFate]

Your routers have to be configured to forward DHCP/BOOTP packets. Most routers can do this, but some can't. What are you using for routers?

MikeL

 

[itsp1965]

I don't know if Win2003 still has support for it, but you can also use the DHCP relay service on a machine in each of the subnets you want the DHCP server on your home subnet to service. But as ProfFate indicated, it is always preferable to have a router that supports BOOTP/DHCP forwarding

 

[byrne1]

We are hooked into a Net VPN set up for us by our local Bell company and we're using Cisco 1760 routers. I just spoke w/ one of Bell techs and he said we'd have to use a "helper address" (the address of the DHCP server). He's supposed to come by today and show me how to do this.

 

[GlenJohnson]

I agree, you should have forwarding enabled, but you might want to try and configure a w2k machine, just to make sure it's not an xp problem. (Don't care for xp myself when it comes to networking.) Good luck.

Glen A. Johnson
"Fall seven times, stand up eight."
Proverb

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884

 

[Beboen]

Yes, the "helper address" is the address of the DHCP relay server (must only be in the subnets w/o DHCP server). It captures DHCP requests in the subnet it's installed into and then makes the request for the client to the DHCP server.
On your DHCP server you also have to configure multiple scopes for the respective subnets.

 

[skankyman]

I am having the same problem. I have a Microsoft 2000 DHCP server behind a cisco 3600 router. I have 3 T-1s going out to remote sites. At each site I have a cisco 2600. I want to get DHCP to that site and on its own subnet!

I am testing this in a "lab" environment with a cisco 2600 router. I have configured the IP helper-address to my full dhcp server address: X.X.X.X Is this correct?

I can ping both ethernet ports of the router from a workstation with a static IP address. The ethernet ports are on different subnets but I can not ping the dhcp server. So, I can't get an IP address! Please help!!!

 

[GlenJohnson]

See if this helps anybody out.

http://www.faqs.org/rfcs/rfc3046.html

Glen A. Johnson
"Fall seven times, stand up eight."
Proverb

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884

 

[Beboen]

The principle of a DHCP relay is fairly simple. On one subnet install a DHCP server and configure it using multiple scopes (one for each subnet). On the subnets - except the one that has the DHCP server installed - configure a DHCP relay and let it forward the DHCP request to the DHCP server.

Skanky: give yourself a fixed ip and then ping the DHCP server. If this doesn't work your router is malconfigured. The IP helper address or DHCP relay should point to the DHCP server, so I think you're correct. You might need to configure the hop count. This is the max amount of routers between the DHCP relay and the DHCP server. (defaults to 4 in W2K)