[LARTC] Ip route cache problem

[Luca Maragnani]

Hello,
I need some help about a routing problem on a complex configuration.

The problem is that I can't reach from services outside from my DMZ.

The scenario is a gateway linked to three internet connections, so that 
I used three distinct iproute2 tables for routing. The gw is running 
ipvs for balancing over the dmz's servers.

DMZ servers are on 192.168.1.0/24 network, .

Every table has the route to reach :
192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.1

I'm using iptables to NAT a server on my DMZ to reach DNS services outsides:
iptables -t nat -A POSTROUTING -p tcp -s 192.168.1.0/24 -d 151.99.0.100 
--dport 53 -j SNAT --to-source 81.77.88.99

Looking inside the cache I find only the route to reach the dns server, 
but not the one that the dns needs to reach my server:
151.99.0.100 from 192.168.1.2 via 81.77.88.100 dev eth2  src 192.168.1.249
    cache <src-direct>  mtu 1500 advmss 1460 metric10 64 iif eth0

I experieced in the past that reentering the iptables nat command 
worked, but it seems a random effect and not always works.

Thank's in advance,
Luca Maragnani