[Bridge] strange networking behaviour with a bridge in game

Andy Gospodarek andy at greyhouse.net
Thu Apr 5 06:07:07 PDT 2007

On 4/5/07, Peter Warasin <peter at endian.it> wrote:
> hi list
> I have a strange problem here. Maybe it is normal behavior and i search
> within the wrong direction. Probably someone here can give me a hint.
> I have a device (rhel4 kernel 2.6.9) with 3 interfaces. 2 interfaces
> (eth0, eth2) are bridged together (br0) and the bridge device has an ip
> address assigned (
> Another interface (eth1) has assigned
> So far so good. Everything is working well if traffic passes from
> out to if both networks are on different
> switches.
> The thing begins to become strange if both eth0 and eth1 are connected
> on the same switch (eth2 is not connected). So i have both subnets on
> the same switch (for testing purposes).
> If i then would like to access, packets reach the device
> through the interface eth1 instead of eth0/br0, which in fact is wrong.
> The arp table on the client shows this also. is assigned
> to the mac adress of the interface eth1.
> Needless to say that this happens only from time to time. If i cleanup
> the arp table sometimes it went alright.
> What's wrong with my installation?
> Thank you in advance!
> peter
> --
> :: e n d i a n
> :: open source - open minds
> :: peter warasin
> :: http://www.endian.com   :: peter at endian.com
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Check out the ip sysctl/proc arp_ignore

net.ipv4.conf.tun0.arp_ignore = 0
net.ipv4.conf.eth0.arp_ignore = 0
net.ipv4.conf.lo.arp_ignore = 0
net.ipv4.conf.default.arp_ignore = 0
net.ipv4.conf.all.arp_ignore = 0



arp_ignore - INTEGER
        Define different modes for sending replies in response to
        received ARP requests that resolve local target IP addresses:
        0 - (default): reply for any local target IP address, configured
        on any interface
        1 - reply only if the target IP address is local address
        configured on the incoming interface
        2 - reply only if the target IP address is local address
        configured on the incoming interface and both with the
        sender's IP address are part from same subnet on this interface
        3 - do not reply for local addresses configured with scope host,
        only resolutions for global and link addresses are replied
        4-7 - reserved
        8 - do not reply for all local addresses

        The max value from conf/{all,interface}/arp_ignore is used
        when ARP request is received on the {interface}

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