Two routers on the same network


I have a small network with 60 PCs. Right now the network is a mess, with several switches cascading each other. We have a Linksys BEFSR41 connected to one of our switches to give us access to the internet (8Mbit cable connection). All the PCs have the Linksys's IP address as their default gateway.

Recently we've installed a new Cisco 2800 router to give us access to our corporate offices. All internet traffic should be routed through this router, so we are going to disable the Linksys router.

But for now I would like to have the two routers connected simultaneously to the network to do some tests, so that some PCs can connect to the internet through the Linksys and the others from the Cisco.

What I've done is that I've set some PCs to have the Linksys IP address as their default gateway and the other have the Cisco IP address as their gateway.

Although at first it seemed to work, people started complaining that the internet connection through the Linksys was unstable. I set up my PC to go through the Linksys and in fact the connection was strange. I could open a web page, and sometimes it would be fast, sometimes slower, other times it wouldn't open at all. Disconnecting the Cisco from the network immediately resolved the problem.

Can someone please tell me what is the problem with this setup? I don't even know if I'm supposed to be able to connect two routers on the same network.

Thanks in advance for any help.

Best regards, Meireles.

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I'd guess that the routers are sharing routing information, you might try disabling routing protocols like RIP etc and maybe suppress ICMP redirects. For such a simple network there are probably other protocols that are not doing any good (e.g. CDP).

Of course, in theory, routing protocols should be a help rather than a hinderance so there is probably something else at the root of the problems. Nevertheless I'd turn RIP etc off.

I'd expect a network sniffer like wireshark would reveal some interesting information about what is going on.

My only qualifications for the above advice are that I have a simple LAN with two routers, each with concurrent Internet access until I phased out one ISP. One router is a Cisco, the other a Netgear. In the past I have had some PCs using one router and other PCs the other for Internet access, just as you describe. I did't have the problems you reported.

Reply to
Ian Wilson

RIP is active on the BEFSR41 and probably cannot be disabled on it (except possibly by disabling routing mode, which would disable NAT.)

Reply to
Walter Roberson

The above RPI theory is worth checking out.

Also you may wany to turn off Proxy ARP on the cisco. And maybe ICMP redirect too?

conf t int [inside-one] no ip proxy arp no ip redirect

(from memory so may not be exact)

If you wanted, you could check the routing tables and arp caches on the various devices to see if they have what you expect

cisco: sh arp sh ip route

windows route print arp -a

before blindly turning thing off.

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