I'm trying to configure my server to route different packets via different
kernel route tables. I thought I had things configured properly, but from
some quick tests, return packets from my server don't seem to be making the
return trip. I look at my iptables log output and see that my packets are
formed as I would expect, but the logs on my router don't show them showing

Is there a way I can verify / validate that my packets are acutally using
the routing table I have specified and are being retransmitted to the
correct gateway?

My setup is as follows (RHEL 4):
# iptables -t mangle -A PREROUTING -d -j MARK --set-mark 3
# iptables -t nat -A POSTROUTING -m mark --mark 3 -j SNAT --to-source
# ip rule add fwmark 3 table 3
# ip route add unicast default via table 3

My goal is as follows:
My server is multi-homed; the same NIC serving both and
I'm looking to configure it such that any packets destined for get a mark added to them. Any response to that packet will
get routed to gateway (from the default route in table 3),
and have its source address modified to

However, if I check my logs on my router at, I don't see any
return packets showing up.

Is there any way I can debug (using tcpdump somehow? Although not quite
sure what to look for in its output - help would be appreciated how best to
use it) the outgoing packets to ensure that they are being sent to, and not my default gateway from my main routing table?



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