connect two internet routers to one LAN

March 8, 2011 at 12:17:19
Specs: Windows XP, Server 2003
how do i connect two internet routers to one IP address range?

I currently have one broadband router connected on subnet
I have a second line which is a copper ethernet EFM 2Mb line connected using a Cisco 1800 router configured on subnet
no DHCP is configured on either router. the dhcp is provided by a windows 2003 server on our LAN which is also configured on the same LAN IP range.
if i connect the Cisco router into the same switch as the broadband router my network devices stop working and dont respond. if i check the broadband router it shows all the connections to it as having the same MAC address as the Cisco router?? if i disconnect the Cisco router everything returns back to normal and works perfectly.

What I want to achieve is to be able to run both routers on the same LAN to provide internet access by configuring the pc's to route through a specific router. the DHCP I want to stay routed through my original broadband line. at the same time i want all pc's to access to the lan devices (ie. servers and printers)

if anyone can advise what the correct configuration would be for the two internet routers would be I would be very appreciated.

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March 8, 2011 at 12:32:12
First a ip addressing lesson.

If you want to use the same lan subnet you need to use the same mask.

You have one at and the other

Correct the subnet mask issue and you should be fine though how you are going to use dhcp to assign different gateways should be interesting.

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March 8, 2011 at 13:02:46
Hi Wanderer,
Thanks for replying so quickly :-)
Yes its been a long day :-) theres no option to set the gateway in DHCP on server 2k3.
The bit that im confused by is why the Cisco router is fudging the existing devices that are currently configured on the subnet.

Would i be correct in thinking that I can configure both internet routers on the same subnet with an IP in the range of 172.16.0.X ? and still have the server broadcasting IP's? or is this the reason the devices are stopping working becasue DHCP dosnt know which router to talk to?

as you can tell Im a bit rusty on networking protocols, but I really appreciate your guidance.

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March 8, 2011 at 13:56:12
dhcp server has no knowledge/cares about the routers. Its only job is to hand out ip addresses when requested.

If is your primary subnet mask than that is what should be configured on the cisco routers lan. It is OK to have one router at .3 and the other at .245

Neither router should be doing dhcp serving so this needs to be disabled on both routers.

Everything was working. If your ipconfig is on you can't talk to anyone on the network

What is still a mystery is what two internet connections are going to do for you.

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March 8, 2011 at 15:06:10
Many thanks Wanderer, appreciate your time in posting. I will give it another try on the same subnet.
the reason we needed another internet line is the location of the office was really far from exchange and thus broadband was very poor. the office has many users trying to get online and was swamping the small line speed. we just installed some pc's that do video conferencing and the equipment is critical it has at least 2Mb upstream bandwidth, so due to location we had to opt for a copper ethernet EFM circuit which supplied 2Mb both ways guaranteed. we couldnt afford a full leased line, too expensive. hope that helps understand reason for the extra line.

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March 8, 2011 at 16:23:11
Video needs to be on its own network. Running it in common with the data network is a huge problem.

Do you have managed switches? You need to consider vlans to start but I build completely different networks for video from data.

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