if this is the wrong place to ask this please just send me a better choice. Ime trying to set a router to do source NAT with a fixed translation table as i believe to be common with firewalls. in the testing stage my: inside net is 10.0.30.0/24 outside net is 10.0.31.0/24 the router itself is running RH advanced server 4 mostly 'out of the box' and on boot logs: Linux version 2.6.9-5.ELsmp (bhcompile@xxxxxxxxxxxxxxxxxxxxxxxxxx) (gcc version 3.4.3 20041212 (Red Hat 3.4.3-9.EL4)) #1 SMP Wed Jan 5 19:30:39 EST 2005 the router is ip 199.218.109.251 and its outside router is a cisco 6513. for testing the cisco is forwarding 10.0.30.0/24 and 10.0.31.0/24 to the 251 ip. router interfaces (of intrest) : eth2 Link encap:Ethernet HWaddr 00:0F:1F:66:2D:8B inet addr:199.218.109.251 Bcast:199.218.109.255 Mask:255.255.255.0 inet6 addr: fe80::20f:1fff:fe66:2d8b/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 eth3.930 Link encap:Ethernet HWaddr 00:0F:1F:66:2D:8C inet addr:10.0.30.1 Bcast:10.255.255.255 Mask:255.255.255.0 inet6 addr: fe80::20f:1fff:fe66:2d8c/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 for testing I have flushed iptables: iptables -F have: echo "1" > /proc/sys/net/ipv4/ip_forward [root@dorm-test ~]# ip route show 10.0.30.0/24 dev eth3.930 proto kernel scope link src 10.0.30.1 199.218.109.0/24 dev eth2 proto kernel scope link src 199.218.109.251 default via 199.218.109.1 dev eth2 [root@dorm-test ~]# [root@dorm-test ~]# ip rule show 0: from all lookup local 32766: from all lookup main 32767: from all lookup default [root@dorm-test ~]# at this point a pc on the inside running 10.0.30.5 (static) can ping my desktop (on anouther segment also off the cisco) tcp dumps along the way show icmp requests and replys as expected. then i : [root@dorm-test ~]# ip route add 10.0.31.5/32 via 10.0.30.5 [root@dorm-test ~]# ip rule add from 10.0.30.5 nat 10.0.31.5 [root@dorm-test ~]# ip route flush cache [root@dorm-test ~]# the pings stop. on the router input i can see the requests still comming with. [root@dorm-test ~]# tcpdump -nn -i eth3.930 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth3.930, link-type EN10MB (Ethernet), capture size 96 bytes 15:34:06.474482 IP 10.0.30.5 > *.*.146.31: icmp 64: echo request seq 2251 but all is quiet on eth2 and my desktop sees nothing. after tests: [root@dorm-test ~]# ip route show 10.0.31.5 via 10.0.30.5 dev eth3.930 10.0.30.0/24 dev eth3.930 proto kernel scope link src 10.0.30.1 199.218.109.0/24 dev eth2 proto kernel scope link src 199.218.109.251 default via 199.218.109.1 dev eth2 [root@dorm-test ~]# ip rule show 0: from all lookup local 32765: from 10.0.30.5 lookup main map-to 10.0.31.5 32766: from all lookup main 32767: from all lookup default [ can anyone get me on to the next step: Thankyou, Stephen Beck, Marietta College.