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i cant figure out how to set Linksys WRT54G Wireless Router to use modem`s DHCP server.

My network scheme is like this:

[COMCAST MODEM] <=> [HUB]
       |              | 
   [LINKSYS]      [SERVERS]
      |||
   [COMPUTERS]

Here is the situation: my modem works as DHCP server, and it works fine. But linksys router has its own DHCP server and its breaking the network all the time (IP conflicts). I solved this problem (for a while): I set different IP ranges on both devices, 10.1.10.10-100, 10.1.10.200-250. And it works.

Before i had Apple Airport Extreme wireless router which was set to bridge mode. So it was using modem`s DHCP server.

Im looking how to do this with Linksys Wireless Router ?

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migrated from serverfault.com Aug 21 '09 at 20:29

This question came from our site for system and network administrators.

5 Answers 5

I had a WRT54G in this exact situation.

  1. Ensure your modem / router (in your case a Comcast Modem) to hand out DHCP addresses.
  2. Ensure your modem and your Linksys both have IP addresses on the same subnet, but different addresses (192.168.1.1 and 192.168.1.2 are good examples)
  3. Disable DHCP on your Linksys.

This is a sort of 'pass-though' - the Linksys will route all DHCP requests through to the rest of the network - where the router will catch them.

Since the rest of the network is on the same LAN as the Linksys, it shouldn't be given any dramas by NAT. Just don't use the WAN port.

I've used this exact setup for several years, and it has worked flawlessly. I can even take my wireless point to a friend's house and use it - especially if he has a different subnet, it won't interfere, and doesn't require any setup (again, the pass-through effect).

Edit: And if you have need of a 5th port, the WRT54G has the ability to use the WAN port as a LAN port. I'm not sure where it is, it's been a while since I replaced my WRT54G, but it's a superb unit.

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+1 - That's how I've setup many of these in peoples homes. I personally put have the WRT54G as the DHCP as I know its interface more than the modem's. –  Hondalex Aug 26 '09 at 22:14
    
That's fair. It's all up to personal preference. Leaving your modem to do the DHCP means it's easier to move the WRT54G around to other networks, if you're crazy like me in that fashion :) –  EvilChookie Aug 26 '09 at 22:16

I could be misreading your question, but if you are merely having trouble making settings changes to to a Linksys, make sure you're using Msft IE, not Chrome or FF.

I my experience, saves in the latter two don't stick. Probably a poorly written script or a permissions problem across tabs.

If you're wondering about setting up two DHCP servers in a small net, be aware that you might be doing double NAT-ing, which is an overhead you don't need and will almost certainly break IPSEC VPNs.

My choice would be to plug the router into the cable modem, plug all the others into the router and give fixed addresses to the server while giving DHCP responsibilities to the router (and disabling it on the modem).

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I would expect it to just pick the dns addresses up through DHCP but if it was me then I wouldn't do that, I'd use the opendns addresses from opendns.com much faster and more reliable plus you can do all sorts of clever stuff.

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http://192.168.1.1

the very first screen has the option to disable DHCP. This may let DHCP be issued by the modem.

If not, you can change the address of the router and/or the start address of DHCP. We have set some Linksys routers to issue out 172.16.1.* and the 10.1.10.* addresses for various reasons.

Depending on your existing setup, you could let the Linksys handle DHCP for everything. I wouldnt recommend this for large businesses, but its definitely doable.

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Why not plug the hub into the router and just let the router handle DHCP? The servers should be on static IPs anyways.

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