Comments on: Should DHCP be running on the DSL modem or on the wifi router?

Question: Should DHCP be running on the DSL modem or on the wifi router?

neilkod — Thu, 03 Jan 2008 17:25:56 -0800

DHCP served up by the DSL Modem or the wireless router?

I received a new DSL modem (actiontec m1000) and have a chance to correct all of my networking wrongdoings of the past. Besides the actiontec, I have a Linksys wrt54g 802.11b/g router, a couple of laptops, and an Xbox with the MS wireless adapter. Previously, the wrt54g acted as a dhcp server, and the only way I could (seemingly) access my DSL modem was to plug a machine directly into it and telnet into 10.0.0.1.

I'd like to know which services are appropriate to run on the modem and which should be running on the wrt54g. I'm running standard linksys fw right now, I used to run the custom stuff a few years ago but I never really saw the advantage of it, so I switched back. I'm willing to give the custom firmware another shot.

Additionally, whenever I would connect to Xbox Live in H3, I would receive a message about NAT not being configured to the fullest-I dont really remember the exact error, hopefully one of you knows about it.

By: rbs

rbs — Thu, 03 Jan 2008 17:50:06 -0800

If you have the router (assuming you're doing NAT and not "real" routing) connected to the DSL, then having your DSL modem give out addresses would make no difference, cause your DHCP Requests won't make it through the NAT. In other words, you're gonna have to do it on the Linksys.

By: TeatimeGrommit

TeatimeGrommit — Thu, 03 Jan 2008 17:56:26 -0800

DHCP is typically served up by *both* the router and the modem. Also, many modems are configured to only give out one address (my cable modem does this). In such a case, the linksys must serve DHCP in order to allow all the different machines to get out through the modem.

I put as much of the load on my router as possible so as to make it easier to switch between ISPs and broadband technologies. For instance, imagine if fiber becomes available in your neighborhood. You don't want hours of customization work in your DSL modem at that point since you'll be throwing it away.

By: neilkod

neilkod — Thu, 03 Jan 2008 17:57:11 -0800

Sorry, I forgot to ask about NAT, which machine should I be using to configure NAT?

By: grabbingsand

grabbingsand — Thu, 03 Jan 2008 18:11:55 -0800

I let the DSL Modem/Router manage DHCP, as well as NAT. My D-Link router is serving as simply a bridge and wireless access point.

~~Bellsouth's~~ AT&T's user interface is not pretty, but it is effective. Both DHCP and NAT and port forwarding and so on are all considered part of the modem's "advanced" suite.

It is important, however, to disable the DHCP on your wireless router, lest ye have conflicting efforts. While the end result might be a connection to the Internet, problems will become apparent soon enough. Torrents fail to go green. Online games fail to connect.

The drawback, of course, is that it is likely that your wireless router will become no longer addressable via its IP address. So if you need to adjust your security settings, do that before shutting down its DHCP.

(Of course, this is all from experience that has been successful for me. I might be doing it all wrong.)

By: fogster

fogster — Thu, 03 Jan 2008 18:37:21 -0800

I don't like to touch the cable company's equipment. I have my own router on the other side that does all that stuff.

Part of my reasoning is that I don't trust the cable company. My friend just had an "upgrade" for her cable setup that disabled wireless. So I leave them to screw with their provided equipment, and have my own router on the other side of it that they can't touch. It does all my DHCP, filtering, and so forth.

If you set your routing tables up right (and you're not using 10.0.0.1/24 as your internal LAN), you could still access the modem, but I'm not sure why you'd want to.

I don't understand the error. Our network runs perfectly configured the way you had it previously. Might it have been some sort of unintentional problem?

By: neilkod

neilkod — Thu, 03 Jan 2008 18:37:53 -0800

Additionally, do I need to give my wrt54g a specific IP address, or should I let the Actiontec assign it?

By: fogster

fogster — Thu, 03 Jan 2008 18:37:55 -0800

Substitute any references in my post to "cable" to "DSL." I have cable, you have DSL, but my advice is the same.

By: fogster

fogster — Thu, 03 Jan 2008 18:41:36 -0800

As for the wrt54g... It has two 'sides' -- the WAN (to the Actiontec), and the LAN (to you).

It gets its WAN address from the DSL modem. This should be automatic. As far as the Actiontec can tell, you've plugged one "computer" into it.

You set up the LAN address manually, and all of your computers use that LAN IP as their gateway to the Internet.

By: Megafly

Megafly — Thu, 03 Jan 2008 18:47:36 -0800

I'd put the DSL modem on Bride and have your router act as the pppoe connector for the entire network.

but that's me.

By: Megafly

Megafly — Thu, 03 Jan 2008 18:47:55 -0800

bridge with a G

By: pompomtom

pompomtom — Thu, 03 Jan 2008 19:31:28 -0800

I do what Megafly suggests. Put the modem into bridged mode, and then you can pretty much forget about it, and do your PPPOE from the WRT. This will also make port forwarding/firewall tuning MUCH easier, which (speculation warning!:) I think will make fixing your Xbox issue a lot easier.

By: samsara

samsara — Thu, 03 Jan 2008 22:25:42 -0800

I'd contact your ISP for the IP assigning question. I know you wanted an answer here but I think your best bet is a quick call with them to get it all set up.

Typically a DSL modem can act as both a bridge and a router (a bridge simply acting as a passthrough adapter with no IP needed). What you may find out, especially after power outages, is that your modem might auto-sense whether it is connected to a router or not...if it doesn't detect one on the internal network it'll switch itself to router mode.

That might not be the case with your modem of course...but regardless, you'll want to have your router ideally take care of DHCP and NAT, and let your modem simply bridge the connection to your ISP. Avoid setting up the modem as another router if possible...that just adds an extra hop you don't really need (and more troubleshooting when figuring out network port mappings). Good luck!

By: damn dirty ape

damn dirty ape — Fri, 04 Jan 2008 05:16:50 -0800

You dont want two routers both doing dhcp/NAT duties. Make the modem a bridge and have the linksys do all the heavy lifting.