topic Re: NATing down an IPsec tunnel in General Topics

NATing down an IPsec tunnel

SteveBoyd — Sat, 30 Jul 2022 14:47:00 GMT

I've got a PA-850 with fairly typical many-to-one NAT outbound to the internet, and some IPsec tunnels. Due to one partner that I'm connecting to with IPsec using 10.0.0.0/8 on their network (don't ask), I need to NAT my 10.28.1.0/24 subnet to 172.28.1.0/24 going to/from their end. I've got a working tunnel for two other subnets (a 172.19.x.x and 192.168.x.x), but I cannot get the NAT working correctly for this third subnet. I've tried several different combinations, including narrowing the NAT down to a single IP 10.28.1.28 <-> 172.28.1.28 but I don't get any hits on the NAT policy and the Traffic logs do not show any 10.28.1.28-sourced traffic pointed at the partner destination.

10.28.1.0/24 is on Trust-L3 (interface Eth1/5), and the IPsec zone is Denver-IPsec (tunnel.5).

Attached is a screenshot of two different rules that are still not working.

Can someone help with either a troubleshooting pointer or what element I'm missing?

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Re: NATing down an IPsec tunnel

SutareMayur — Sun, 31 Jul 2022 15:50:32 GMT

Hi @SteveBoyd ,

Attaching the traffic log may give some more clarity on the issue. You can also verify the traffic logs again and confirm what source and destination zone and routes are matching for the traffic that you are looking at.

For the NAT that I am seeing in the attached file, I am seeing you have configured Bi-Directional NAT. Do you have your IPSEC configured in Bi-Directional, I mean both end will act as sender as well as responder? If yes, why there is one more rule which is dynamic one?

Also, can you check routing configuration for subnet 172.28.1.0/24 ? You need to make sure to point its route to the desired tunnel interface.

Incorrect/missing routing configurations may cause matching the wrong destination zones, so please verify routing once.

Hope it helps!

Mayur

Re: NATing down an IPsec tunnel

laurence64 — Mon, 01 Aug 2022 08:00:54 GMT

I agree with @SutareMayur I would definitely check routing for the NAT range.

Re: NATing down an IPsec tunnel

SteveBoyd — Tue, 02 Aug 2022 22:26:39 GMT

Thank you both for your help!
The reason there was two rules is I figured I'd create one for each direction. In practice, the one worked and the other didn't, and then thanks to your helpful nudge I realized that I hadn't enabled bidirectional on the one that was working. Another element was getting the security policies set as well; apparently (correct me if I'm wrong) while the NAT policies get processed before the security policies, if the NAT is working but security rules don't allow the traffic, it still won't increment the NAT or show up in the traffic logs.

I've tweaked it, disabled the nonworking NAT policy, and updated the security policies needed additional to the existing in and out policies for the IPsec tunnel. Attached are the working NAT policy and security policies for this, for the benefit of others with a similar question.