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New Member

Q: PIX Outbound NAT on Site-to-Site VPN connection ?

Hi,

I have a PIX515e running 6.3(1) / PDM 3.0

configured as follows

PAT for general Internet connection

VPN for remote access

Site-to-Site VPN

I've been asked to add an additional Site to Site

VPN link but with outbound NAT.

Looking through the Cisco docs the closest example

config is a Site-to-Site VPN with overlapping private

IPs - but this seems to require some combo of a global IP and NAT in my ISPs router (!!).

Is this possible using a PIX (I could do it using

"normal" router + IOS) ?

Many Thanks,

6 REPLIES
Cisco Employee

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

Can you provide some more detail on exactly it is you want to do? Just saying "VPN link but with outbound NAT" is a little confusing.

Thanks.

New Member

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

Hi,

I'm looking to hide the internal IP addresses behind a mutually acceptable IP range. I want to

use something from rfc1918 (private IPs) as a

transit for the site-to-site link.

If I were using IOS, I'd use ip pool, access-lists and nat statements to map out/inbound connections

to the transit ip pool.

Given that I've already using the outside i/f

for PAT (internet access) and a remote access VPN

is this possible ?

Many Thanks,

Cisco Employee

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

OK, so you want all your internal hosts to appear as some pre-defined IP address when it goes through the tunnel to the remote network.

Assuming your local network is 10.1.1.0/24, the remote network is 10.2.2.0/24 and the IP address you want the 10.1.1.0/24 network to appear as is 10.5.5.5, you should be able to do the following:

> access-list 100 permit ip 10.1.1.0 255.255.255.0 10.2.2.0 255.255.255.0

> nat (inside) 60 access-list 100

> global (outside) 60 10.5.5.5

> access-list 160 permit ip host 10.5.5.5 10.2.2.0 255.255.255.0

> nat (inside) 0 access-list 160

> crypto map L2L 10 set peer x.x.x.x

> crypto map L2L 10 match address 160

> crypto map L2L ......

Since NAT happens BEFORE encryption, you can NAT the L2L tunnel traffic first, then define your crypto access-list to specify the already-NAT'd traffic pattern.

Also, "NAT access-list" will be done before "nat x.x.x.x" so this should take precedence over your standard nat/global pair that you'e defined for the Internet access.

New Member

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

What I understand from the above is that I should be able to nat (PAT) a whole internal subnet to a valid IP address & set a site-to-site VPN using valid IP addresses.

Do I need to still specify the nat (inside) 0 command?Since I am already address translating a private iP to a public IP.

Thanks

New Member

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

Hi,

Well I eventually got around to trying this method on my PIX (sorry it's taken so long).

The access-list 100 .... is OK

The global (outside) 60 a.b.c.d is OK

The nat (inside)60 access-list 100 a big no-no

6.3(1) does not allow this, Command Reference manual

states you can only do

nat (if_name) 0 access-list acl_id

which exempts traffic that matches acl_id from NAT

processing - the opposite of what's required.

Any other suggestions please ?

Regards,

New Member

Re: Q: PIX Outbound NAT on Site-to-Site VPN connection ?

Using

nat(if_name) 60 network networkmask 0 0

should work

Example: nat(inside) 60 10.10.0.0 255.255.0.0 0 0

if you need more networks translated to the same global address just add a similar statement for that network

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