Two routers on the same network

Discussion in 'Cisco' started by meireles, Apr 4, 2007.

  1. meireles

    meireles Guest


    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

    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, Apr 4, 2007
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  2. meireles

    Ian Wilson Guest

    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.
    Ian Wilson, Apr 4, 2007
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  3. RIP is active on the BEFSR41 and probably cannot be disabled on it
    (except possibly by disabling routing mode, which would disable NAT.)
    Walter Roberson, Apr 5, 2007
  4. meireles

    Bod43 Guest

    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

    sh arp
    sh ip route

    route print
    arp -a

    before blindly turning thing off.
    Bod43, Apr 6, 2007
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