Port / IP forwarding using Iptables

On the linux box

iptables -t nat -A PREROUTING -j DNAT -i eth1 -p tcp --dport 25 --to-destination 208.116.51.10:25

Given that the traffic passes through the Linux box before it reaches the Win box. Can you give more details about your IPtables setup ?

iptables -t nat -A PREROUTING  -i ethX -p tcp -d 208.116.12.106 --dport 25 -j DNAT --to 208.116.51.10:25
iptables -t nat -A POSTROUTING  -i ethX -p tcp -d 208.116.51.10 --dport 25 -j MASQUERADE
#replace the ethX with proper values

Sorry - the second rule should have -o
iptables -t nat -A PREROUTING  -i ethX -p tcp -d 208.116.12.106 --dport 25 -j DNAT --to 208.116.51.10:25
iptables -t nat -A POSTROUTING  -o ethX -p tcp -d 208.116.51.10 --dport 25 -j MASQUERADE

Thanks for the quick response , let me try those commands and let u know

Not sure the POSTROUTING rule is necessary, as I believe netfilter "remembers" what's translated, and ensures all further packets are also translated.

Also, as well as ensuring the traffic passes through the Linux box on the way to the Windows box, it is also necessary for the traffic coming back from the Windows box to pass through the Linux box.

Should more help be required, it would be useful to have the network layout explained.

the POSTROUTE rule is required if in and out interface is this same one.

I tried putting both the rules as suggested

iptables -t nat -A PREROUTING  -i ethX -p tcp -d 208.116.12.106 --dport 25 -j DNAT --to 208.116.51.10:25
iptables -t nat -A POSTROUTING  -o ethX -p tcp -d 208.116.51.10 --dport 25 -j MASQUERADE

replaced ethX with eth0 which is my ethernet card on linux.

but it is still not working for me.  

m I missing something ?????

maybe
echo 1> /proc/sys/net/ipv4/ip_forward

what's other iptables rules, like forward?
iptables -L -nx

Following is the output of command
service iptables status


[root@ankh ~]# service iptables status
Table: nat
Chain PREROUTING (policy ACCEPT)
num  target     prot opt source               destination
1    DNAT       tcp  --  0.0.0.0/0            208.116.12.106      tcp dpt:25 to:208.116.51.10:25

Chain POSTROUTING (policy ACCEPT)
num  target     prot opt source               destination
1    MASQUERADE  tcp  --  0.0.0.0/0            208.116.51.10       tcp dpt:25

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

I cannot see the filter table, please run the command I gave. I want to be sure it's not the case. Have You tried enabling ip_forward?

no forward rules i specified only the two commands you suggested ,

yeah ip forwarding is enabled using echo 1> /proc/sys/net/ipv4/ip_forward

also loaded iptable_nat module using modprobe iptable_nat

As this is my first attempt to work with linux server , i may miss even the simple and obvious things

[root@ankh ~]# iptables -L -nx
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

just to add , we have multiple static ips configued on the linux box  follwing is the output of ifconfig command.

[root@ankh ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:208.116.12.106  Bcast:208.116.12.111  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3549405 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3591896 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:499253541 (476.1 MiB)  TX bytes:600212498 (572.4 MiB)
          Interrupt:16 Base address:0xe000

eth0:1    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:208.116.12.107  Bcast:208.116.12.111  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:2    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:208.116.12.108  Bcast:208.116.12.111  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:3    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:208.116.12.109  Bcast:208.116.12.111  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:4    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:208.116.12.110  Bcast:208.116.12.111  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:5    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.73  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:6    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.74  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:7    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.75  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:8    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.76  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:9    Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.77  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

eth0:10   Link encap:Ethernet  HWaddr 00:0C:76:0F:0C:79
          inet addr:216.67.224.78  Bcast:216.67.224.79  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xe000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:246 errors:0 dropped:0 overruns:0 frame:0
          TX packets:246 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:14032 (13.7 KiB)  TX bytes:14032 (13.7 KiB)

Please let me know in case you need any other info , or any other command output to diagnose the problem further.

Both Linux and Windows Box are hosted on Data Center ( static ip) and accessible from internet.

Thanks ravenpl , Things are working now ... Thanks a lot for your help.....

Real nice job , Thanks a lot. Credit is all yours. And hope you will be always be there to help you in future too.

THANKS A LOT