I thought I would blog on this. It could be useful for someone who might have an IOS router instead of an ASA and need to create a IPSEC Site-to-Site VPN to a remote peer, then NAT VPN traffic to a different address or subnet if needed, or the local subnets conflict with each other.
Here is a nice little Visio to kind of show what I am going for with the traffic:
Because of duplicate subnets on both sides, I need to nat traffic going to 18.104.22.168 from 192.168.10.10, otherwise traffic should flow normally. How can I achieve conditional nat? By using a route-map and then natting only the traffic in the Route-map. So, lets get our VPN setup first. Remember, we add the NAT network or host IP to our interesting traffic ACL that will be used to define our Phase2
These are my commands:
ip access-list extended VPN-to-Remote permit ip host 10.255.232.10 host 172.20.0.192
crypto map Crypto 6 ipsec-isakmp set peer 22.214.171.124 set transform-set Transform match address VPN-to-Remote
That pretty much gets the VPN up and going. Now for the interesting part – we need to create a new ACL, match my private 192.168.10.10 address and the destination address of the remote server, then match that ACL in my Route-map.
ip access-list extended Nat-for-VPN permit ip host 192.168.10.10 host 172.20.0.192
route-map VPN-to-REMOTE permit 10 match ip address Nat-for-VPN !
Great! So, we now have the route-map created.. so now what? We need to create a NAT statement that references my Route-Map. Then of course with any VPN we need to modify the “NO-NAT” ACL to include the traffic for both the 192.168.10.10, and the 10.255.232.10 to my remote destination.
ip nat inside source static 192.168.10.10 10.255.232.10 route-map VPN-to-HCN extendable
ip access-list extended NO-NAT deny ip host 10.255.232.10 host 172.20.0.192 deny ip host 192.168.10.10 host 172.20.0.192
Now, if we try to access the remote side, does it work? Yes it does, but lets check to see if our nat is really working. It is! As you can see, 192.168.10.10 going to 172.20.0.192 is being natted into 10.255.232.10, but all other traffic gets natted out of the WAN interface.
Lets just check for translations of 10.255.232.10
Bingo, everything works great. Lets make sure that we are getting hits on our Route-Map.
Below shows how to configure Static nat for a web server or some kind of application running on a internal host. Basically we are port forwarding port 80 from our public IP of 126.96.36.199 to port 80 of our internal IP at 10.1.1.2. In this example Auto Nat will be used. You could also use Manual nat, I have written another blog entry on this. This is way different than 8.2 and below. Here we create an object and then modify the object with the Static port forward we want. I
In this example my ASA outside IP is 188.8.131.52, and I want the web server to answer on 184.108.40.206.
Somethings to note- We could name the objects anything, I just chose to use the actual IP address. For example, you could do the command ” object network Webserver-Outside” and use that name to reference the outside IP address.
Next, if I want to allow access to 10.1.1.2 from the outside world, I will need an ACL.
access-list Outside-In permit tcp any 10.1.1.2 eq 80
access-group Outside-In in interface outside
Notice the internal IP specified in the ACL – that is there on purpose. Instead of referencing the External IP you now reference the internal.
What if the outside address answering for my web server is the outside IP of the ASA?
No problem, just have to modify that one NAT entry. Instead of the public NAT object we use the “interface” keyword.