Nowadays with a limited number of IPv4 addresses using PAT is very common. Many hosts on our internal network hiding behind a public address. Have you ever wondered how the table is very common when using PAT, and what's possible for us to retrace ASA?
First, some theory. ICMP is a protocol layer 4 and is zdefiniowamne in RFC 792 We call it the Internet Control Message Protocol and is widely used in the diagnosis of the network. How we use there "types" and "Cody", we will focus on two: type 0 and 8 code 0, which correspond to echo reply and echo request.
In short, if you type on your computer ping <IP will be sent an ICMP type 8 code 0, and if we are lucky we will be sent an ICMP type 0 code 0
As I mentioned in RFC 792 on page 13 is defined as a package should look for types 0 and 8: