Dear sir we have windows based network with fix ip address using dsl line And have iis Noew we want to install firewall between internet and our server such that whatever traffic coming it wiill first recived on linux box and depend on port if its www or ftp then it must redirect to windows machine i try iptables and use command

iptables -t nat -A PREROUTING -p TCP -d 192.168.10.4 --dport 21 -j DNAT --to 192.168.10.10:21

but its not redirecting any packet to ftp if i try to run ftp locally or from local net.
ALSO IF I USE
#netstat -t it show me state SYN_SENT and SYN_RECIV
but if i try TO DO
iptables -t nat -A PREROUTING -p TCP -d 192.168.10.4 --dport 21 -j DNAT --to 192.168.10.4:22
THEN ITS REDIRECTING ME TO SSH PORT IF I TRY FTP FROM LOCALLY OR FROM MY LAN ..

can u help me solve this problem

regards

chandrakant