[CentOS] ipsec nat issue

Steve Clark sclark at netwolves.com
Sat Oct 13 18:31:55 EDT 2012


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
>
>


-- 
Stephen Clark
*NetWolves*
Director of Technology
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark at netwolves.com
http://www.netwolves.com


More information about the CentOS mailing list