Double Portforwarding or Natting

as long as the devices doing the NAT support port translation, it should work fine.  I guess your linux server is dual homed and functioning as a router?

Linux server is dual homed and functioning as a router .... Yes, thats correct
Hmm, I think I must be doing something wrong in the port forwarding rules on the Linux Server .... This is what I used.

iptables -A FORWARD -d 192.0.0.2 -p udp --dport 161 -j ACCEPT
iptables -t nat -A PREROUTING -d 10.156.13.101  -p udp --dport 1161 -j DNAT --to-destination 192.0.0.2:161

and then did service iptables restart

I'm new to Linux so am not sure If I need to change script files of IPTables to make this rule functional or what ..... My Router is able to port forward 5161 to 1161 but my linux cant port forward 1161 to 161 to an access point ... Access Point is a normal D-link configured with the correct community string ....

By the way, this port forwarding am doing is to basically make SNMP work; I'm interested in monitoring the access points rather than the Linux Server or the Router ! and these access points are Natted behind the Linux Server and the Linux Server is natted behind the Cisco router (and then out to the internet ofcourse)  

Linux box shows my iptable rule for iptables -A FORWARD -d 192.0.0.2 -p udp --dport 161 -j ACCEPT but doesnt show the iptables -t nat -A PREROUTING -d 10.156.13.101  -p udp --dport 1161 -j DNAT --to-destination 192.0.0.2:161 rule in its output ... Plus How can I move it up in the order ..?


[root@pxe sysconfig]# iptables -L -v
Chain INPUT (policy ACCEPT 481 packets, 42165 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     udp  --  tun0   any     anywhere             172.20.0.1          udp dpt:domain
    0     0 ACCEPT     udp  --  tun0   any     anywhere             255.255.255.255     udp dpts:bootps:bootpc
    0     0 ACCEPT     tcp  --  tun0   any     anywhere             172.20.0.1          tcp dpt:bv-smcsrv
    0     0 ACCEPT     tcp  --  tun0   any     anywhere             172.20.0.1          tcp dpt:bv-is
    0     0 DROP       all  --  tun0   any     anywhere             172.20.0.1
    0     0 DROP       all  --  tun0   any     anywhere             anywhere

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     tcp  --  tun0   any     anywhere             anywhere            tcp dpt:pptp
    0     0 ACCEPT     gre  --  tun0   any     anywhere             anywhere
    0     0 DROP       all  --  tun0   !eth0   anywhere             anywhere
    0     0 TCPMSS     tcp  --  any    any     anywhere             anywhere            tcp flags:SYN,RST/SYN TCPMSS clamp to PMTU
    0     0 ACCEPT     all  --  any    tun0    anywhere             anywhere
    0     0 ACCEPT     all  --  tun0   any     anywhere             anywhere
    0     0 DROP       all  --  any    eth1    anywhere             anywhere
    0     0 DROP       all  --  eth1   any     anywhere             anywhere
    0     0 ACCEPT     udp  --  any    any     anywhere             192.0.0.2           udp dpt:snmp

Chain OUTPUT (policy ACCEPT 471 packets, 62709 bytes)
 pkts bytes target     prot opt in     out     source               destination