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How to setup 2 routers for 1 network

I am working on a network with 2 routers which are using 2 different IP addresses and assigning different IP addresses to the computers that connect to them. The routers are also connected to each other through cable. All the PC's have internet connection through this setup but I want to change the routers so that they all communicate on the same IP range.

Right now this is what I have:

Cable modem going into a Linksys WRT54G. This WRT54G router has an IP address of 192.168.1.1 (class C subnet) and is set to assign IP addresses starting at 192.168.1.100.

There is also a Linksys Vonage router RT31P2. This is wired to the WRT54G router. The RT31P2 router has an IP address of 192.168.15.1 and is set to assign IP addresses starting at 192.168.15.100.

All devices plugged into either router have internet connectivity but can not communicate to devices connected through the opposite router.

I have a few hours before I have access to the network but this is my plan:

Assign the RT31P2 router an IP address of 192.168.1.2 and to assign IP addresses starting at 192.168.1.200

Is it this simple? Or is there more to it? I don't want to buy any new hardware as I'm pretty sure I can accomplish my end result with what I have currently: 1 network of IP addresses using 2 routers.
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JF0
Asked:
JF0
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1 Solution
 
Rob WilliamsCommented:
Not quite that simple. I assume you have :
Internet => Modem => Wrt54g => RT31P2
                                       |               |
                                      PCs           PCs

A) you cannot have 2 DHCP servers on the same network/subnet (previously you had 2 subnets)
B) if you assign the LAN side of the RT31P2 an IP of 192.168.1.2 the LAN and WAN side of the router will be in the same 192.168.1.0 subnet, which is not possible for a router. Routers route packets from one network to another. When both are the same, it doesn't know whether to send the packets to the WAN or LAN side, and they are usually lost.

Not to say it can't be done. Just requires a few changes. Can the RT31P2 be your primary router? I am not familiar with the whole "Vontage thing". If so
-connect the WAN port of the RT31P2 to the modem
-enable the LAN side with the IP and DHCP range you wish
-on the WRT54G assign it an IP in the same subnet
-again on the WRT54G, disable DHCP all together
-once more on the WRT54G, remove any WAN configuration
-wireless configuration will be as normal
-connect a LAN port of the RT31P2 to a LAN (not WAN) port of the WRT54G

Now all clients wired or wireless connected to either router will be on the same subnet, all will get their IP's from the Vontage unit, and all will have Internet access.

If the Vontage cannot be the primary you can revers the order and configure similarly.
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JF0Author Commented:
It sounds as if what you are saying is what I had planned originally except I need to turn DHCP off on the 2nd router? If so, how do I assign static IP's to devices connected to the 2nd rounter?
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Rob WilliamsCommented:
>>"sounds as if what you are saying is what I had planned originally"
Sorry, sounded like you were still making use of both WAN ports.

>>"I need to turn DHCP off on the 2nd router? If so, how do I assign static IP's to devices connected to the 2nd rounter?"
You can assign static to anything you like. If dynamic, any device connected to the second router is now on the same network, and will request a dynamic/DHCP address from the first router. The devices do not have to be physically attached to the router from which they get their DHCP address.

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JF0Author Commented:
"The devices do not have to be physically attached to the router from which they get their DHCP address."

So could I just setup the RT31P2 to assign DHCP starting at 192.168.1.200 and it would assign those IP's even though its IP address is in another subnet? That way all my devices connected to the routers share the same subnet.
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Rob WilliamsCommented:
You can run into problems with 2 DHCP servers on the same network, but as you suggest, so long as they are the same subnet and the DHCP scopes/ranges don't overlap, it will work. The connected device will get it' IP from which ever one it finds first.
However, if you have:
Internet => Modem => WRT54G => RT31P2
With the WAN port of the RT31P2 connected to the LAN port of the WRT54G it should not work, as the packets cannot get routed properly.
The reason I suggested connecting the Vonage unit to the modem is I suspect traffic has to pass through it to take advantage of your Vonage service.
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JF0Author Commented:
I see what your saying with the WAN port. I just verified and the PORT1 from the WRT54G  is plugged into the Internet port of the RT31P2. I was assuming they were connected by regular ports, is that possible?
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Rob WilliamsCommented:
>>"is that possible?"
Not sure of the question.
You can't have the WAN port plugged in and everything on the same subnet, and I don't think you can unplug the WAN port and have Vonage. That is why you will probably have to make it the primary router and plug it's WAN port into the modem.
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JF0Author Commented:
Ive been talking to the guy at the network over the phone and this is how we are setup now. The routers are connected both via port 1 and have dhcp pools starting at 100 and 200 respectivly. All computers plugged into either router can talk now. However, surprisingly, even though the vonage router is set to assign from 200, the pc connected to it has an ip address of 192.168.1.102. But everything seems okay for now.

Only problem is it dosnt seem like the phone is obtaining a new ip address, no dial tone... but other than that I think we are good unless you can see some future issues?
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Rob WilliamsCommented:
>>"surprisingly, even though the vonage router is set to assign from 200, the pc connected to it has an ip address of 192.168.1.102."
It could be an IP that hasn't been renewed, or as I said they are on the same LAN and the PC's will get an IP from which ever DHCP server it finds first, both are available to assign IP's to any connected device.

>>"unless you can see some future issues?"
"it dosnt seem like the phone is obtaining a new ip address, no dial tone" that might be one issue.  <G>


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bbrunningCommented:
I'm not sure how vonage routers work either but if you want them all to communicate on the same ip range you need to put the vonage router connection right after the cable modem. Then change your linksys router to be only a gateway and plug the cable from the Vonage router to the WAN port of the linksys. From there the vonage router should grab internet/phone from the cable/dsl modem give out dhcp to all clients connected to it, then send that info the linksys and the linksys should just forward all that info to the rest of the clients whether they are phone's or PC's.
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Rob WilliamsCommented:
>>""it dosnt seem like the phone is obtaining a new ip address, no dial tone" that might be one issue.  <G>"
Reading the on-line manual, as assumed, the phone will not get an IP unless the Vonage router has an Internet connection trough it's WAN port. It will also support the WRT54G when connected as an access point, so the initial configuration I listed in my first post, should work fine for both routers, phones, and PC's. Let us know how you make out with it.
--Rob
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scrathcyboyCommented:
The limit of TCP/IP networking is that any one physical device can have only ONE correct IP to address it.  Therefore turn off your redundant router and keep it as a FAILOVER in the event the first one dies.  Simply run ONE router at a time, that is all you have to do, the rest of the logic is OK, but they cannot run concurrently to assign duplicate IP numbers to the one device, like a NIC.  TCP/IP requires that any one device like a NIC resolves to only ONE UNITUE IP Address.  Period.
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bbrunningCommented:
In other words, review robwill's comments
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The--CaptainCommented:
>The limit of TCP/IP networking is that any one physical device can have only ONE correct IP to address it.

>TCP/IP requires that any one device like a NIC resolves to only ONE UNITUE [sic] IP Address.  Period.

Wrong. Period.

Physical interfaces may have many associated IPs - usually one is designated as the primary IP, but this is fairly arbitrary given a decent router with policy routing and source nat functionality..

I'd say RobWill has a good handle on this one.

Cheers,
-Jon
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JF0Author Commented:
And the solution:

Cable Modem > Vonage Router > 4 port Wireless Router

Setup the vonage router as normal with DHCP (192.168.1.1, 255.255.255.0, DHCP range 192.168.1.100). Setup 4 port Wireless router as a switch and not a router by assigning it an IP within the subnet of the Vonage router, in this case 192.168.1.25 and turn off DHCP on the wireless router. Connect a regular port from the vonage router (port 1) to a regular port on the wireless router. Reboot modem, vonage router, wireless router.
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Rob WilliamsCommented:
Excellent, sounds good.
Thanks JFO,
--Rob
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