How to run two routers/ISPs on same network ?

  brynclarke 13:31 20 Nov 09

I have two phone lines (lucky me) and have been running a home network for several years without problems (actually, with loads of problems, but it all sort of works-ish).

I have a Vigor 2600G ADSL router with USB printer, a couple of NAS, some HomePlugs with a secondary Wireless Access Point, a wired-in desktop, and several wireless laptops, PS3, Squeezebox etc.

The router is configured to allocate DHCP addresses above, and the NAS, PS3 etc have static IP addresses below that.

I am about to switch to a new ISP, using the other phoner line. They have sent me a new router (DLINK 2640R).

What I would like to do, at least for a period, is connect the two routers, and use the new one only to access the internet, leaving the old network configuration more or less untouched. When all is working I can switch off my old ISP.

In oder to do this, there are some thinks I do understand I need to do, and others I don't.

What I do understand I must do:-
1. Connect the new router to a laptop and use its web configuration pages to:-
a) give it a new static IP address e.g.
b) Turn off its DHCP function
c) Reboot it
2. Connect its LAN socket to spare LAN socket on old router.

What I don't understand is:-
1. How I tell my wired-in desktop, and wireless laptops, to use the internet connection at instead of, but continue to use for other network functions e.g. DHCP
2. If I can switch between the different internet connections on the fly
3. What to do about DNS
4. What other things that I don't know I don't know?

All help gratefully received

  mgmcc 14:40 20 Nov 09

If you configure the new router with an address of, disable its DHCP server and connect one of its LAN ports to a LAN port on the old router, it will perform only as a basic Network Switch or Wireless Access Point. It *WON'T* perform as a Router to serve internet access to the connected client devices - they'll continue to get internet access from the old router, albeit possibly via a connection to the new router.

I cannot see the merit in not simply connecting all devices to the new router for both LAN and Internet access, particularly if everything operates in the subnet. If the routers were to operate in different subnets, and the computers had two network adapters installed, they could connect simultaneously to both routers. You could then selectively disconnect one router from the internet (phone line).

  brynclarke 21:02 21 Nov 09

Many thanks for the input. All my devices have a single network connection so your last suggestion is not practical for me.

I don't wish to switch everything across at the start for two reasons:-
a) I want to make sure the new ISP service is OK before I commit to it - I want to parallel run for a period.
b) I don't want to have to reconfigure all my devices in one go, which will take me a half day - I want to be able to put in an hour here and there till it is all transferred across.

So what do I have to do to use the new router for internet access while using the old one for LAN and WAP - switch on its DHCP and disable DHCP on the old one, or change to IP addresses so the old router is .5 and the new is .1 - or what? Again, all help greatly appreciated.

  mgmcc 21:53 21 Nov 09

>>> So what do I have to do to use the new router
>>> for internet access while using the old one for
>>> LAN and WAP

If the new router is to provide internet access to all devices, they will all have to be connected to it and therefore that will be the LAN. You can't separate "internet access" and the "LAN", using a different router for each function.

In any case, there shouldn't be anything major to reconfigure in order to move over from the old router to the new. You can ensure the new router operates in the same subnet as the old one and that it has the same SSID for wireless networking. The "network" shouldn't then be aware that there is a difference.

I can't help thinking that you're trying to overcome a problem that doesn't really exist.

  brynclarke 14:29 22 Nov 09

My problem is simply to switch over to a new ISP, on my other phone line, without having to reconfigure all my wireless devices to use the new Access point, and my wired-in devices too, on Day 1.

Since the last post, I have configured the new router as, turned off its DHCP connected it to the old router, and reconnected my HomePlug connections to it. Everything seems fine - Internet is still via old router/phone line/ISP. so I am just using it as a switch.

When the new ISP connection goes live, I now believe what I have to do in order to use it instead of the old, is:-
a) Update old router's DHCP configuration to change "Default gateway" from to, so that my dynamic-IP devices (laptops) use the new router as their internet gateway
b) Reconfigure the "Default gateway" on each of my static-IP devices similarly, so they also use the new router for internet access.
c) Because my old Router (though not the new) allows me to configure the "Default Gateway" it assigns when it allocates dynamic IP addresses, I believe I do not have to disable DHCP on the old router and switch DHCP on on the new.

What I still don't know is:-
a) If this will work
b) What, if anything, I should do to DNS configuration on old and new routers

  brynclarke 15:26 22 Nov 09

Aha! Penny just dropped - mgmcc, your thinking is that I can just swap out old router, swap in new router, set to same SSID & WEP password etc as old router, then no network devices need to change configuration.

Reason I can't do that is the printer - old router has USB port for printer, new one doesn't, so I need to keep both in my LAN, and deal with DHCP issues etc. But I can certainly, when new ISP is working, disable wireless on old router and set new to same SSID etc. However, the internet connection issue is what I needed to get my head round, and that is, I believe, determined by the "Default gateway" configuration rather than which router is serving as wireless access point....?

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