Never mind. I got it to work. I already had the ping going when I added the iptables SNAT rule, conntracking or route caching made it not work. I stopped the ping for a minute or so then restarted it and it worked and did the SNATing as I expected.

On 10/13/2012 06:04 PM, Steve Clark wrote:

Hello,

I have the following setup on linux 2.6.32... CentOS 6.x :

ipsec tunnel eth0-10.255.3.254/25 - eth1-pub add1 <-> eth1-pub add2 - eth0-10.255.5.254/25

I am trying to SNAT remote private address 10.255.5.128/25 packets when they come out of the ipsec tunnel to make it appear like it was from local address 10.255.3.254. I am doing a source ping from the right side to a device on the left subnet ping -I 10.255.5.254 10.255.3.129 but it doesn't work - see below.

iptables -t nat -I POSTROUTING -o eth0 -s 10.255.5.128/25 -d 10.255.3.128/25 -j SNAT --to-source 10.255.3.254

Chain POSTROUTING (policy ACCEPT 6 packets, 456 bytes) pkts bytes target prot opt in out source destination 0 0 SNAT all -- * eth0 10.255.5.128/25 10.255.3.128/25 to:10.255.3.254

$ sudo tcpdump -nli eth0 icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 15:20:17.772396 IP 10.255.5.254 > 10.255.3.129: ICMP echo request, id 52588, seq 62, length 64 15:20:18.777272 IP 10.255.5.254 > 10.255.3.129: ICMP echo request, id 52588, seq 63, length 64 15:20:19.772572 IP 10.255.5.254 > 10.255.3.129: ICMP echo request, id 52588, seq 64, length 64 15:20:20.770681 IP 10.255.5.254 > 10.255.3.129: ICMP echo request, id 52588, seq 65, length 64

I would expect 10.255.5.254 to be replaced with 10.255.3.254 what am I missing? Is this possible I could do it when we were using FreeBSD.

I didn't find anything googling.

Thanks, Steve