Imam slednia problem s ipchains policy FORWARD: 

Taka raboti: 

Chain forward (policy MASQ): 
target prot opt source destination ports 
MASQ all ------ 10.12.1.0 anywhere n/a 
MASQ all ------ 10.13.2.0 anywhere n/a 
MASQ all ------ 10.14.3.0 anywhere n/a 
MASQ all ------ 10.15.4.0 anywhere n/a 

A taka ne raboti: 

Chain forward (policy ACCEPT): 
target prot opt source destination ports 
MASQ all ------ 10.12.1.0 anywhere n/a 
MASQ all ------ 10.13.2.0 anywhere n/a 
MASQ all ------ 10.14.3.0 anywhere n/a 
MASQ all ------ 10.15.4.0 anywhere n/a 

Zashto se poluchawa taka. Server-a e na Debian. 
 Ami trubwa P forward da e ACCEPT poneje shte iska da pusna
dwa realni ip adresa tam.

 Ot tova koeto si napisal bi triabvalo da raboti i po dvata
 nachina, default policy  se izpolzva sled kato se mine po
 tsialata veriga na user defined chains (man ipchains). A tova
koeto iskash da napravish se pravi taka:
/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -s localnet/mask -d any/0 -j MASQ
...
/sbin/ipchains -b -A forward -s real_IP1 -d any/0 -j ACCEPT
...

Uspeh