Re: NIC War

From: dircha (dircha_at_dircha.com)
Date: 04/19/04

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    Date: Mon, 19 Apr 2004 16:19:28 -0500
To: debian-user@lists.debian.org

    Ian Melnick wrote:
    > The only problem was, external requests coming in weren't going anywhere.
    > There's some kind of switch at the "main office" that forwards requests
    > from the "external IP" to the "internal" one, which is what my first NIC
    > was set up for. When we used arping and other monitoring tools, it showed
    > the second NIC responding---when a request was made for the MAC of the
    > first NIC, the second card would respond with its MAC. I think this had
    > been happening all along, according to arpwatch's flip-flop reports, but
    > maybe this is different.

    This seems to be the problem. Forgetting external requests for now, this
    seems to be something that should not be happening. Let's try to isolate it.

    nic1 and nic2 are on the same machine

    nic1: ipA, macA
    nic2: ipB, macB

    On the network attached to nic1 one you send an arp request:
    "who-has ipA tell x.x.x.x"
    where "ipA" is the ip you believe is assigned to nic1. nic1 does not
    respond. nic2 responds with:
    "ipA is-at macB".

    Is this what is happening? If this is occurring, and proxy_arp is not
    enabled, doesn't this seem to indicate a serious problem?

    At the time of this flip, according to the local machine is the
    assignment still as follows (still correct)?

    nic1: ipA, macA
    nic2: ipB, macB

    > The first NIC works fine, AFAIK, since you can use arping to ping it
    > via its MAC. However, when you ping it via its IP, the other card
    > responds. Again, I've manually set the arp table on the server machine
    > and on the client I used to ping it, but it didn't help.
    >
    > I tried disabling the second nic to see if the first one would then
    > correctly reply to arp requests again, and it did---only problem was,
    > external requests still weren't coming in.
    >
    > I also changed the gateway of the second nic to be the same as the
    > first nic, to avoid the second one going through it. Didn't help.

    What do you think, could this indicate a problem with nic2 or its
    driver? Are nic1, nic2, and nic3 all the same model and using the same
    drivers? Have you tried replacing nic2 with a nic you know to work, or
    if you know nic3 to be working, temporarily with nic3?

    dircha 

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