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82 posts

Master Geek

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Topic # 151242 18-Aug-2014 22:09
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Hello, I have a client PC in the 192.168.3.0/24 network behind a Fortigate firewall which performs NAT.
This firewall is likewise connected on the 192.168.4.0/24 network to my ADSL router which also performs NAT.
So I have double NAT going on from my client PC, out to the internet.

My client PC can ping it's default gateway on the 192.168.3.0 network (Fortigate firewall interface 192.168.3.254). My client can also ping to the internal interface of the ADSL router (192.168.4.254). But my client cannot ping out to the internet.

It would seem that double NAT is causing this. My question is how does double NAT prevent the pings from the client to the internet working ?

Thank you for any help in me understanding this.

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Ultimate Geek
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  Reply # 1110895 18-Aug-2014 22:44
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Switch the ADSL router to bridge mode? Double NAT is a nightmare.

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Ultimate Geek
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  Reply # 1111043 19-Aug-2014 08:46
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Double NAT isn't recommended but should work okay, certainly for ping anyway!

I would do a traceroute from your client PC and see where the traffic is stopping. On your Fortigate I assume you have the routing set such that it knows to send everything to the upstream router?

Matt

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  Reply # 1111045 19-Aug-2014 08:48
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Is it just ping that doesn't work, or all traffic? If it's just ping, I would suggest one (or both) of the devices have rules around ICMP traffic (or lack of relevant rules).




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  Reply # 1111073 19-Aug-2014 09:23
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+1 for one of the routers blocking the PING.  Having several layers of NAT is not fantastic but it should not cause significant issues either as best I am aware.




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