IPtables: SNAT & Aliasing

kegwell · 01-05-2005, 07:54 PM

I currently have a running, funtional firewall. I have 1 external interface (eth1). I have aliased/multihomed additional external ips to that interface as well (eth1:eth1a, eth1:eth1b...etc). I have associated a few of the aliased IP's to an interal IP and the routing works fine inbound. For example, if I hit $ETH1:ETH1A I will be directed to 192.168.0.100. Although, I am having problems with SNAT. When I set up a rule for all outbound traffice from 192.168.0.100 to go out $ETH1:ETH1A, it just goes out eth1. When I try to specift the -o (outbound interface) as eth1:eth1a it still resuilts back to eth1. Even when I specify the aliased IP address explicitly it comes back to the ip of eth1.

Any help would be appreciated. Thanks in advance.

twsnnva · 01-05-2005, 08:44 PM

You can't use aliases. You would need to do this.

Code:

iptables -t nat -A POSTROUTING -s 192.168.0.100 -o eth1  -j SNAT --to $PUBLIC_IP_OF_ALIAS

Thomas

kegwell · 01-05-2005, 08:55 PM

Yeah I tried that, but it did not work...I found out what the problem was though...

Code:

iptables -t nat -A POSTROUTING -s 192.168.0.100 -o eth1  -j SNAT --to $PUBLIC_IP_OF_ALIAS

was entered after

Code:

MASQUERADE  all  --  0.0.0.0/0            0.0.0.0/0

Once i reversed the order everything worked fine. Thanks for the help!