Linux box (ex-router) causing duplicates on Windows/Linux LAN

Discussion in 'Linux Networking' started by Jamin, Jan 26, 2004.

  1. Jamin

    Jamin Guest


    Small LAN setup at home. Big problem. I have three Linux boxes and a
    Windows XP box running Winroute connected to the 'net, doing NATting
    and firewalling me (yeah, it *can* be done with Windoze).

    Up until now, I didn't have a hub, so was using a setup similar to

    [intif] Winbox [extif 213.x] <--> INET
    [eth0] Linux1 [eth1]
    Linux2 [eth0]
    Linux3 [eth0]

    In this scenario, Linux2 and Linux3 were setup to route via Linux1, no
    iptables/chains involved, just ip forwarding. Linux1 had a
    well-config'd routing table so as to send packets in the right
    directions, and Winbox took care of Internet connectivity, port
    forwarding to Linux3 (mail/newsserver) etc.

    Now I've got a mega 100Mbps UTP hub, and I thought, hey, I don't want
    all that messy cabling, lets just plug everything in together. I
    removed eth1 from my 'bridge' (Linux1) and I set the routing tables on
    Linux1, 2 & 3 the same:

    $ ip route dev eth0 scope link dev lo scope link
    default via dev eth0

    so I know the default gateway is config'd ok. When I bring up Linux2
    and/or Linux3 -- no problems, everyone 'sees' each other, and I've got
    full connectivity between Linux boxen, the Windoze box can see the SMB
    shares and the Internet flows thru.

    *However* Linux1 (ex 'bridge') seems to be stuck in its ways. It comes
    up ok, lets me talk to the other Linux boxes, and (for a while) to the
    Windows box, then all networking dies. If I do an 'ifconfig eth0 down'
    on Linux1 everything's ok again, so I've isolated it to this box. The
    routing table and default gateway is _identical_, promiscuous mode is
    definitely OFF, and tcpdump/ping has told me that I'm producing
    duplicate packets when PINGing Linux1--->Winbox. I'm going over the
    config on Linux1, but TBQH I don't understand why, if the routing
    table/default gw is identical, it should be creating all these
    problems on its own, _except_ that it's 'history' is as a simple
    router, somewhere, something is on that shouldn't be. Anyone got any
    pointers, things to check? I'd appreciate *any* input... I could post
    tcpdump logs, but they'd only confirm what I've established [bandwidth
    save mode=on].



    Jamin, Jan 26, 2004
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  2. Jamin

    Jamin Guest

    (Jamin) wrote in message
    I have since found out that putting the network card on the Windows
    box in promiscuous mode cures the problem, not exactly a solution; and
    my Windows knowledge on how to do this is limited to starting a packet
    sniffer... the network driver for SMC cards doesn't have a setting --
    however this could be indicative of the *cause*. Windows problem ~
    windows solution, tho' I still think it lies on the Linux box.


    Jamin, Jan 26, 2004
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