topic Re: Port Forward in Operating System - Linux

Port Forward

Lorenzo Facello — Wed, 10 Oct 2007 02:53:34 GMT

Hi all,
i have a problem with port forward.
I' ve three linux box:
Gateway, Proxy and Server.

My network is 172.20.0.0
Gateway has ip 172.20.0.1 and 192.168.0.1
Proxy 192.168.0.2
Server 192.168.0.3

On Gateway there is
$IPTABLES -t nat -A PREROUTING -i $ETH_LAN -p udp -s 172.20.0.0/16 --dport 161 -j DNAT --to-destination 192.168.0.2

On Proxy
iptables -t nat -A PREROUTING -p tcp -i eth0 -d 192.168.0.2 --dport 161 -j DNAT --to-destination 192.168.0.3

Default Gw of Proxy and Server is Gateway

From my client on 172.20.0.0 LAN i can't query snmp thee Server, why?
Thanks

Re: Port Forward

Stuart Browne — Wed, 10 Oct 2007 06:00:11 GMT

You have your SNAT rules for the packets going the other direction?

Re: Port Forward

Steven E. Protter — Wed, 10 Oct 2007 06:25:09 GMT

Shalom,

Need to see the entier iptables configuration. Not your block lists but configuration.

I hate iptables and use http://www.fs-security.com Firestarter wherever possible.

For diagnosis, turn on logging.

SEP

Re: Port Forward

Zeev Schultz — Wed, 10 Oct 2007 06:31:25 GMT

Why you set "-p udp" on gateway and "-p tcp" on Proxy? Put udp if you want to use port 161.

See also

http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch14_:_Linux_Firewalls_Using_iptables