Source NAT on a IPSec VPN tunnel due to overlapping IP space.

nson2139 — Tue, 16 Jun 2020 07:41:48 GMT

Folks,

Our team has been tasked to work on a VPN tunnel from a customer premises to our corporate DC.

The access would be unidirectional with the Customer accessing on-prem resources.

The first challenge is that we have overlapping IP addresses at the customers end.

Our team wants to use some NAT policies which will act like a 1:1 policy. i.e. we want to avoid a interface based NAT.

There should be some way of identifying the IP address individually on the IPS behind the VPN Palo Alto firewall.

Any suggestions?

Thanks!!

Re: Source NAT on a IPSec VPN tunnel due to overlapping IP space.

OwenFuller — Tue, 16 Jun 2020 18:19:14 GMT

I would think you could do with a Dynamic IP NAT to achieve the 1:1 NAT you're wanting (see https://docs.paloaltonetworks.com/pan-os/9-0/pan-os-admin/networking/nat/source-nat-and-destination-nat/source-nat.html ). However, I think if you're doing this on the corporate side, you're going to have a problem with conflicting routes (10.10.10.0/24 is both down the tunnel, and on the LAN). If you could do this at the customer side before it crosses the tunnel, that might be better.

EDIT: Actually, the more I think about it, that's going to cause the same problem on the other side then. Maybe you'll have to NAT both directions with two different pools that don't conflict with the 10.10.10.0/24 address. Maybe you translate 10.10.11.0/24 to 10.10.10.0/24 on the corp side, and you translate 10.10.12.0/24 to 10.10.10.0/24 on the client side or something like that.

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Source NAT on a IPSec VPN tunnel due to overlapping IP space.

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