topic Re: NAT RULE - IPsec VPN in General Topics

NAT RULE - IPsec VPN

joseglez — Tue, 21 Apr 2020 03:26:20 GMT

Hello all,

I am implementing an IPsec VPN and I have to NAT the source IP address, but I am very confused with the bidirectional source NAT,

Lets say my local IP=192.168.1.1 (natted to 1.1.1.1), remote IP in the other side of the VPN= 10.10.10.1

For example If I configure:

Src Zone Src IP Dest Zone Dest. IP NAT

Internal 192.168.1.1 VPN 10.10.10.1 source nat: 1.1.1.1 (bidirectional)

behind the scene the returning NAT rule created will be:

Src Zone Src IP Dest Zone Dest. IP NAT

Any Any VPN 1.1.1.1 dest. nat: 192.168.1.1

My confusion is based in the fact that 1.1.1.1 is not in the VPN zone, its a external IP in the External zone so I think I cannot use bidirectional NAT in this scenario and I have to create 2 rules for each direction like:

Src Zone Src IP Dest Zone Dest. IP NAT

Internal 192.168.1.1 VPN 10.10.10.1 source nat: 1.1.1.1

Src Zone Src IP Dest Zone Dest. IP NAT

VPN 10.10.10.1 External 1.1.1.1 dest. nat: 192.168.1.1

Am I wrong about this?

Re: NAT RULE - IPsec VPN

SutareMayur — Tue, 21 Apr 2020 07:10:52 GMT

@joseglez,

First of all, is it bidirectional tunnel (both sides will be initiator and responder) then only you need BI-Directional NAT ?

If only any of the side is initiator and other responder, then you don't need Bi-Directional NAT.

Now you want to NAT IP 192.168.1.1 with 1.1.1.1, in this case,

1. IP 1.1.1.1 shouldn't be part of VPN ZONE. Destination IP addresses will be part of VPN zone (i.e. 10.10.10.1 ). Just make sure you have route towards desired tunnel interface for this IP/network.

2. Configure proper NAT Rule. So IP 1.1.1.1 would be consider to be part of internal as it is going to DNAT with internal IP 192.168.1.1

3. Also make sure NAT IP 1.1.1.1 is part of proxy ID configuration.

Hope it helps you!

Mayur

Re: NAT RULE - IPsec VPN

joseglez — Wed, 22 Apr 2020 02:48:18 GMT

Hello @SutareMayur,

Yes, it will be bidirectional.

I agree with you when you said that 1.1.1.1 shouldn't be in the VPN. Since that is what paloalto would do if I select bidirectional source NAT,

that is why I think I may have to use 2 unidirectional rules.

I do not quite understand when you said that: "IP 1.1.1.1 would be consider to be part of internal as it is going to DNAT with internal IP 192.168.1.1"

Do you mean, when creating the reverse rule, instead of external I should put Internal as dest zone??

Re: NAT RULE - IPsec VPN

SutareMayur — Wed, 22 Apr 2020 06:39:11 GMT

@joseglez,

Yes, for reverse rule (inbound traffic), you need to put destination zone as internal not external. Then only traffic will be forwarded to internal IP 192.168.1.1. Normally while hosting internal server also, we configure policies in same way.

Your NAT would be like -

Bi-Directional NAT

SZONE - Internal

S-IP - 192.168.1.1

DZONE - VPN

D-IP - 10.10.10.1

S-NAT-IP - 1.1.1.1

Security Policy for outbound traffic -

SZONE - Internal

S-IP - 192.168.1.1

DZONE - VPN

D-IP - 10.10.10.1

Security Policy for inbound traffic -

SZONE - VPN

S-IP - 10.10.10.1

DZONE - Internal

D-IP - 1.1.1.1

Also configure proper routes and proxy-id configuration. With this, everything should work as expected.

Hope it helps!

Mayur

Re: NAT RULE - IPsec VPN

joseglez — Wed, 22 Apr 2020 14:20:40 GMT

Great, thank you @SutareMayur

I included the after NAT IPs in the proxy IDs also.