1st lets look at a typical vendor hosted-business-server topology
Each client LAN network address needs to be unique. Clients that are using rfc1918 addressing , has no means to delegate and ensure unique address are being used between customers. So cust1 might be using the same 192.168.1.0/24 block as cust2 or cust3, and you have no control as to what the customer may or may not be using.
If the vendor grows his business-server environment by adding more customers, this problem could be a nightmare to manage.
So how do we ensure that each customer who access the business servers domain, are using a unique address?
By source NAT'ing the client machines to a public address that he/she owns, we can ensure that all customers are unique from the vendor's hosted business server perspective. In a true remote business-server application farm that supports multiple customer, this is how they ensure uniqueness.
In this blog, I will demo a configuration that you can use just for this & that's typically deployed within the cisco ASA firewall. It would allow any one of the 3 above customer to use the same local lan subnet addressing, and all client's machines would be NAT'd to a public address that they own.
This address would than be present to all connections to the business-server domain across the vpn-tunnel.
Let's say Customer1 owns a public address of "126.96.36.199". And their local lan is 192.168.1.0/24. So customer 1 will NAT his rfc1918 space behind the "188.8.131.52" address and present this to the business servers located at 192.168.254.0/24 for all connections establishment.
The Vendor firewall is located at 10.1.1.1 and requires AES128/256, DHgrp2, no PFS. They are using a PSK of "cust1psk", and will allow the customer full access to the 192.168.254.0/24 block.
Cust configuration ( Cisco ASA ipsec type L2L vpn )
Crypto Ikev1 policies
The Encryption ACL
NOTE: This encryption ACL will encrypt the sNAT global outside address across the encryption domain.
Crypto-map & Transform-set
(2nd) NAT rules for SNAT based on the destination of 192.168.254.0/24
To summarize this SNAT scenario;
Freelance Network & Security Engineer
kfelix -a--t- socpuppets ---d--o--t--- com
=( * * )=