IPsec Traffic and Networks
There are two important issues you might have to deal with concerning the sending and receiving of IPsec traffic:
Other IPsec issues
The following three sections will discuss these issues in more depth.
IPsec and Address Translation
Address translation translates addressing and, possibly, port information inside IP, TCP, or UDP headers. My goal here is to not discuss what address translation is; I’m assuming you are already familiar with it. My other Cisco Press book, Cisco Router Firewall Security, covers the mechanics of address translation on Cisco routers, if you’re not that familiar with the process.
As you already know, there are three IPsec connections between two IPsec peers: