Re: A weird routing question.

On 09/28/2007 09:44 AM, Ken Sims wrote:
Hi -

On Thu, 27 Sep 2007 19:36:35 +0200, none <""testr\"@(none)"> wrote:

On a linux box 'A' which has interfaces eth0, eth1, eth2, eth3, I would
like to do a special treatment on packets incoming via eth0 and whose
source is <some-network>.

I would like these packets be unconditionaly redirected unmodified for
output via interface eth1.

That is:
- even if they were targeted (destination IP) at my box 'A', they will
be re-emitted through eth1.
- even if they would have been forwarded through eth2 or eth3, they
will be re-emitted through eth1 too.

If they would be forwarded anyway, advanced routing can be used to
force them out a specific interface.

For packets whose destination is 'A', I think you would need to do
something with netfilter to get the packets on to the forwarding
chain, but I don't know how without changing the destination IP
address.

If forwarding is enable, which indeed should be, on this machine
acting/imitating as router, I on Redhat like machines shall create an
alias eth1:0, whereas on Debian and, or Ubuntu I shall use
iproute/iprute2 as follows:

# ip addr add dev eth1 local net.wo.rkX.host/ne.tm.as.kX

I OTOH, am curious to know, how netfilter/iptables can forward packets?
Do we have kind of some FORWARD target for PREROUTING chain?

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