NAT - Inside Outside Local Global

One of the reasons that we're still able to use IPv4 addressing it down to NAT which stands for Network Address translation.

There are 3 types of NAT:

1) NAT overload a.k.a PAT (Port Address Translation)

2) Static NAT

3) Dynamic NAT

Let's take a look at the nomenclature before we discuss the difference types of NAT. We need to understand the following terminology (link to cisco site explanation):

1) Inside 2) Outside

3) Local  4) Global

In the image above, the 10.0.0.10 IP address is our 'Inside Local' IP address. 

The 174.6.69.123 IP address is our 'Inside Global' IP address.

 The 123.124.125.126 is the 'Outside Global' IP address.

The Outside Local address is hard to explain so let's just state what's on the Cisco website -> "The IP address of the outside host as it appears to the inside network."

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Cisco commands:

Say on interface gig0/0 you have the internal IP of 10.15.0.10/24 and on interface gig1/0 you have access to a web server at 192.168.0.100/24.

> conf t

# int gig0/0

# ip nat inside

# int gig1/0

# ip nat outside

# ip access-list standard IP-LIST

Note: below 0.0.255.255 is a wildcard mask which is the opposite of a subnet mask.

# permit 10.15.0.0 0.0.255.255

# exit

# ip nat inside source list IP-LIST int gig1/0 overload