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Old 09-14-2009, 11:30 AM   #1
Registered: Dec 2006
Location: London, UK
Distribution: Centos, Fedora
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Question packet coming through one interface route out via another interface and SNAT also

I have box1 with ip ang GW
This box also has an alias of

i have the ip of another box, box2 to and the GW to, but box2 can not reach the internet. It can ping both ips of box1 but no internet.

the network is not currently catered for in my company.

I am thinking that if i can create some iptable NAT rules on box1 that will accept any packets coming in on and then send it out through, at the same time changing the source ip to since 172.16.0 network is not catered for.

I dont know if my idea is possible, if it is how do i implement this on iptables.

If it doesn't work, other solutions are welcome.

Old 09-14-2009, 12:42 PM   #2
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you need to turn on ip forwarding as well echo 1 > /proc/sys/net/ipv4/ip_forward (typically you can set it permanently in your sysctl.conf file)

then just add a rule like iptables -t nat -A POSTROUTING -o eth0 -s -j MASQUERADE
Old 09-14-2009, 06:56 PM   #3
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It Works, thanks estabroo

I have modified it a little

iptables -t nat -A POSTROUTING -o eth0 -s -j SNAT --to-source

from my scouring through the internet, masquerade is for dynamically assigned ip's and SNAT is better suited for static IP's.

Last edited by saiyen2002; 09-14-2009 at 08:10 PM.


iptables, routing

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