ASA IPsec Remote Access VPN | NAT Question

Question

We have a situation where a company that needs remote VPN access to our network is having an IP conflict with our subnet.  I know this is a common issue and can often be resolved on the client side by changing the metirc on the network interface, but I am looking for a better solution on our end so I do not have to suggest workarounds.
Part of the problem is likely that our subnet is "too big", but I'm not going to be changing that now.
We are using 10.0.0.0/24 and the remote is using 10.0.11.0/24 and 10.1.0.0./16
I played around with some NAT rules and feel that I am missing something  I am looking for suggestions, please.
Thank you.

Answer 1

Hi,
This depends on your ASA firewalls software version and partly on its current NAT configurations.
I presume the following
Interfaces "inside" and "outside"
VPN Pool network of 10.10.100.0/24 (or some 192/172 network)
Software 8.2 and below
access-list VPN-POLICYNAT remark Static Policy NAT for VPN Client
access-list VPN-POLICYNAT permit ip 10.0.0.0 255.255.255.0 10.10.100.0 255.255.255.0
static (inside,outside) 192.168.10.0 access-list VPN-POLICYNAT
Key things to keep in mind with this software level is that if any of our internal hosts on the network 10.0.0.0/24 also have a "static" configuration that binds their local IP address to a public IP address then you might have to insert the above configuration and then remove the original "static" command and enter it back again.
This will change the order or the "static" commands so that the original "static" command wont override this new configuration as they are processed in order they are inserted to the configuration. The remove/add part is just to change their order in the configuration
Software 8.3 and above
object network LAN
subnet 10.0.0.0 255.255.255.0
object network LAN-VPN
subnet 192.168.10.0 255.255.255.0
object-group network VPN-POOL
subnet 10.10.100.0 255.255.255.0
nat (inside,outside) 1 source static LAN LAN-VPN destination static VPN-POOL VPN-POOL
In the above configuration we do the same as in the older software versions configuration but we have the number "1" in the "nat" configuration which places it at the very top of your NAT configurations and therefore it applies. No need to remove any existing configuration and enter them again like in the old software
In addition to the above NAT configuration you naturally have to make sure that the traffic to the NATed LAN network goes to the VPN. So if using Split Tunnel the NAT network needs to be added to the VPN ACL. If using Full Tunnel then naturally everything should already be coming through the VPN. I imagine though that you are using Split Tunnel, or?
Hope this helps
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- Jouni