ASA Config: Site-to-Site VPN with NAT

Christmas just went by and I had some time to write down an howto with NAT in an Site-to-Site VPN tunnel. In this scenario you have clients in site A who need to access servers in site B. Normally it is not possible to access the servers in site B when you’re using the same IP address space. You can only get this work if you’re using NAT in site A to hide the internal addresses. The only thing what you need to do is to find an address space for the NAT translation and you need to be sure that you’re not using the address space in site B where you want to access the server.

Its just an very easy example how to do that you can also do an configuration where you site A and B access each other so you need todo NAT on both sides and create an transfer network. If you have questions there just ask i will maybe also create an howto for that,

Site A

Internal IP address space:

Client IP addresses:

NAT IP address:

Site B

Internal IP address space:

Server IP addresses:

Configuration Site A:


object-group network Site-B-Access

object-group network VPN-Site-B

access-list nat_outbound-site-b extended permit ip object-group Site-B-Access object-group VPN-Site-B

nat (inside) 2 access-list nat_outbound-site-b

global (outside) 2 netmask

object-group network VPN-NAT-Site-B

access-list acl_inside extended permit icmp any object-group VPN-Site-B
access-list acl_inside extended deny ip any object-group VPN-Site-B

access-list acl_VPN-Site-B extended permit ip object-group VPN-NAT-Site-B object-group VPN-Site-B

tunnel-group type ipsec-l2l
tunnel-group ipsec-attributes
pre-shared-key secretpassword
isakmp keepalive threshold 10 retry 2

crypto map VPN 1 match address acl_VPN-Site-B
crypto map VPN 1 set peer
crypto map VPN 1 set pfs group2
crypto map VPN 1 set transform-set ESP-3DES-SHA
crypto map VPN 1 set connection-type bidirectional
crypto map VPN 1 set security-association lifetime seconds 3600 kilobytes 4608000
no crypto map VPN 1 set reverse-route
no crypto map VPN 1 set  nat-t-disable
crypto map VPN 1 set phase1-mode main
crypto map VPN 1 set inheritance rule
crypto map VPN 1 interface outside

Site B:


coming soon

so have a look in some days i will complete the post until then

Just tested new Cisco ASA 8.3 (Update)

It was a big suprise that Cisco changed so many things in the new IOS version for the ASA. Remember it is only an minor release update i would expect these changes for an major update but anyway they did a good work.

The new group objects what they implementent is very nice. It make the work much easier and you have a better overview about the NAT configuration like before because they move it to the actual network object.

Here an example how nat works in the network object:

object network web-01-external

object network web-01-frontside
description Web Server Node 1
nat (inside,outside) static web-01-external