Re: Two NICs, same network...

["Mark L. Wise" <mark@alpha2.com>]

Is this not a routing issue?

route add -host 10.1.1.3  gw <eth2 ethernet address> eth2

This would route all traffic to 10.1.1.3 to eth2

Mark



semi linux wrote:
> On 5/8/07, David Lang <david.lang@digitalinsight.com> wrote:
>> On Tue, 8 May 2007, semi linux wrote:
>>
>> > I've got an odd problem where I've got two NICs on the same network
>> > and I want all traffic to one IP to go out one interface and all other
>> > traffic to use the second interface.  I'm going to try an simplify my
>> > actual setup, because a lot of it makes no difference to this post...
>> >
>> > I know this has to be a iptables sort of setup since the routing table
>> > can only make a difference on different networks and not based on
>> > looking for a specific IP address.
>> >
>> > The question is:
>> >
>> > eth0 IP: 10.1.1.1
>> > eth1 IP: 10.1.1.2
>> >
>> > target: 10.1.1.3
>> >
>> > (these IPs are just examples, there are no hard-fast rules surrounding
>> > the other possibilities)
>> >
>> > How do I make sure this goes out eth1 instead of eth0?  Do I use the
>> > mangle rule with the physdev module?
>> >
>> > I feel like I'm overlooking something or forgetting my basic network
>> > ideas here...
>>
>> you haven't quite given enough info here
>>
>> if you have target2 10.1.1.4 and you want all traffic to target to go 
>> out eth0
>> and all traffic to target2 to go out eth1 then you would want to 
>> start out with
>> defining host routes (the routing table _can_ look at specific hosts, 
>> not just
>> networks)
>>
>> in addition, I believe that you will need to play around with arp 
>> filtering to
>> make sure that each NIC only responds to arp requests for it's IP 
>> addresses.
>>
>> if you really only have one remote IP address and two local addresses 
>> and you
>> want all communications between the target and  10.1.1.1 to use eth0 
>> while
>> all communications between the target and 10.1.1.2 to use eth1 things 
>> get more
>> complicated
>>
>> you would need to look into packet/connection tagging and iptables 
>> routeing
>> decisions.
>>
>> rather then try and go into that right now why don't you try to be a 
>> little
>> clearer about exactly what you are trying to do.
>>
>> David Lang
>>
>
> Ok... you asked for the whole thing, here it is (forget my previous 
> example):
>
> eth0 - 10.1.1.1
> eth1 - N/A
> eth2 - N/A
> br0 (eth1, eth2) - 10.1.1.2
> target - 10.1.1.3
>
> The bridge (br0) is setup using brctl and seems to work w/o problem...
> The eth1 and eth2 IP addresses really don't matter since they are both
> referenced via the bridge and are set to something invalid.  10.1.1.3
> is connected via cross-over cable to eth2 port.  br0 and eth0 are
> connected to my network on the same subnet.
>
> What I'd like:
> - all packets (from the network or local) where destination=10.1.1.3
> to be routed to eth2.
> - otherwise, all traffic from the network to use eth0 for I/O.
>
> Basically, I want to specify that ONLY traffic for 10.1.1.3 is to use 
> eth2.
>

-- 
Mark L. Wise

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