Help Needed: DHCP Routers on Wired/Wireless Network

[LarryG]

I'm having a devil of a time getting two routers to play nice on the same Windows network. One is a Comcast cable modem that is both the Internet gateway and the DHCP "server" that assigns IP addresses to the various clients. The other is a LinkSys wired/wireless router that we need *only* to allow our two iPhone users to connect to our network.

If there's anyone here who (a) *really* knows their Windows networking and (2) is willing to help, please shoot me a Private Message and I'll get back to you in the morning ... for now, I'm heading home for an appointment with the liquor cabinet.

[LCHIEN]

I'm not a super expert but I assume you are plugging the Linksys intothe Comcast router by RJ45 cable.
DHCP assign IP address in an assigned range, usually 192.168.0.Xxx or 192.168.1xx.xxx
the 192.168 part is standard for local subnets and will not clash with addresses on the internet.

You might make sure that the two routers are not assigning addresses in the same range. You can set up the linsysfor example to give out addresses in the 192.168.200.xxx range or even 192.168.0.ZZZ where ZZZ is 200-299 for example.
otherwise you may have machines with conflicting addresses on your local subnet.

[gary]

There are two primary address spaces in networking. 192 and 10 address range at a high level. You can set the linksys to dispense addresses in the 10.10.10.x range if you want to.

The prior suggestion would work but you need to make sure the subnet mask is set to 255.255.255.0 on both routers for it to work properly.

[DaveS]

It sounds like you simply need to disable the DHCP server function on the linksys.

[LCHIEN]

It sounds like you simply need to disable the DHCP server function on the linksys.

if he does that then the wireless devices won't get an address.

[Crash2510]

if he does that then the wireless devices won't get an address.

yes they will because the other router will assign them, while the linksys will just be used as a basic wireless access point. Basically he would be turning off the brains of the router, but it will work.

Sorry I forgot for this to work find out what range of ip addresses your comcast router assigns ex 192.168.0.1 or 192.168.1.1 when you find this out then change the linksys router to something like 192.168.0.254 or 192.168.1.254 only changing the last number then turn off the dhcp feature on the wireless router then it should work.

[LinuxRandal]

Don't know anything about the Iphone. Is it an application, or a product?

If an application, on a laptop for instance. you can set your network up as a profile, and assign it an address, WITHOUT DHCP. Then use a roaming profile elsewhere.

[kevinsa]

yes they will because the other router will assign them, while the linksys will just be used as a basic wireless access point. Basically he would be turning off the brains of the router, but it will work.

That is what I did on our office network. Once you have the DHCP disabled on the wireless it should work fine. The one thing to remember is that the cable modem must be plugged into the LAN port on the wireless router, not the WAN port.

[Kristofor]

DHCP is easy for client devices, but I shudder at the thought of letting the back end infrastructure try to configure itself... Support headache...

Probably the easiest configuration would be to have the Comcast device only connected to the linksys router (which often have a port labled for the "internet connection" or the like, then have all of the client PCs/iPhones connecting to the Linksys as well.

To do that in the Linksys config (generally accessed by going to 192.168.1.1 on a PC connected to it and nothing else attached) you should see an Internet Setup section and a Network Section. In the internet section you can leave it as Automatic Configuration- DHCP and it will pull an IP address for the Linksys router from the Comcast device.

Then down in the Network setup put in an IP address for the LAN side of the router (but not one on the same subnet as the Internet side, so if Comcast gives out 192.168.1.1 set the router's network interface to 192.168.100.1). Then Enable the DHCP Server on the Linksys and click save. Finally connect the Comcast device to the Internet port on the Linksys and powercycle the Linksys (after which you would need to go to the new IP address you gave the router if you want to manage it).


Kristofor.

[crokett]

I would do what Kristofor said and connect the Linksys to the Comcast modem, then connect all the local PCs to the Linksys. Disable DHCP on the Comcast and let the Linksys handle assigning the addresses.

If you insist on only using the Linksys for the iPhones, then you need to do what DaveS said and disable DHCP on the Linksys and at that point you are only using it as a wireless access point.

[LarryG]

Success!

First of all, thanks very much to everyone who responded. I'm grateful for (but not surprised by) the BT3 community's willingness to help out with problems like this.

Secondly, to proceed directly to the punch line, I now have everything working smoothly in all respects.

Third, I should mention that the REAL mystery to all this is that for the last three weeks -- ever since we switched from a DSL line to Comcast cable -- the network has been working flawlessly. But for whatever reason, when we came in to work yesterday morning, everything was hosed. I don't know why. Nothing had changed.

So, yesterday, I tried all manner of variations on most of what was suggested ... making sure the two routers would assign addresses in different ranges, disabling DHCP in the Linksys, more. The closest I could ever get was that all the wired clients could see our LAN and the Internet, and the two iPhones could establish a wireless connection via the Linksys, but for some reason they would not sync email or calendars over the wireless network.

One thing I could not get to work, however, was disabling DHCP in the Linksys and allowing the Comcast router to assign IP addresses to the wireless devices (ie, the two iPhones). With the Linksys configured as a WAP only, and no matter how I plugged in the cables, the iPhones were never assigned an IP address.

So this morning, the first thing I tried, if only because I was working my way down the thread, was Phil's method of disabling DHCP in the Linksys. I don't know what I did differently (because I tried so flippin' many combinations yesterday, I lost track), but this time the iPhones were assigned an IP address by the Comcast router and were able to join the wireless network. They still couldn't sync files, however. And another problem arose: I could no longer manage the Linksys router via the address I had just manually assigned to it. I tried two different addresses and both times had to reset the router to the factory defaults to get back in.

I then tried Kristofor's method and that did the proverbial trick. (I had not tried it yesterday because Comcast had not given us the username and password required to manage their router; I could only work with the Linksys.) As soon as I made the changes Kristofor described, everything worked. The wired clients could all see our LAN and the Internet. The iPhones pulled an IP address, were able to join the wireless network, and, finally, were able to sync their files.

Whew.

Oh, one last thing ... it was not that we were *insisting* on using the Linksys only for the iPhones. I just meant that was the only reason we bought the Linksys router and added it to our wired network. We have cable pulled throughout the building, don't have any laptop users, and almost never have any reason to allow an outsider onto our network. So until the iPhones came into the picture, we didn't need to mess with wireless.

Again, my sincere thanks for all the help, from everyone.