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    SubjectRe: ARP (mis)behavior
    On Fri, 20 Aug 1999, Chris Leech wrote:

    > I'm doing some work with network drivers, and have run across some strange
    > ARP behavior in testing that seems to stem from the IPv4 stack. ARP replies
    > seem to ignore any mapping between devices and IP addresses, so that as long
    > as an IP is assigned to one interface all the interfaces on a given machine
    > will respond to the ARP request.
    >
    > As a simple example, if a server has two Ethernet cards connected to the
    > same network configured as 10.0.0.1 and 10.0.0.2. From a client machine,
    > say 10.0.0.3, pinging both server addresses seems to work, but looking at
    > the ARP cache reveals that often one interface has responded to both ARP
    > requests. More interesting, if one interface is brought down the other will
    > continue to respond to ARP requests and any other network traffic for the
    > downed adapters IP address.
    >
    > In a situation where multiple adapters are on the same network segment, the
    > Linux IPv4 stack behaves as if a many-to-many mapping of a pool of IP
    > addresses onto a pool of network adapters exists.
    >
    > While this does provide some basic fail-over capabilities, I can't imagine
    > that this is expected or desired behavior. If this is the intended
    > behavior, I'd be interested in hearing why ARP was implemented this way. If
    > not, I may have time to try and change this and submit a patch.
    >

    Err.. Do you, per chance, have both network cards running on the same
    network, with the same network address, and a netmask which will allow
    them to listen to the same ARP requests? If so, how could they do
    anything different than you describe?


    Cheers,
    Dick Johnson
    **** FILE SYSTEM WAS MODIFIED ****
    Penguin : Linux version 2.3.13 on an i686 machine (400.59 BogoMips).
    Warning : It's hard to remain at the trailing edge of technology.


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