No Confusion With IP NAT Terms: Inside Outside Local Global

When you are trying to figure out the name for an IP address, Inside Local / Inside Global / Outside Local / Outside Global. Just keep this in mind:

1. Local or Global refers to the current location of the packet.
2. Inside or Outside refers to the location of the device.

Refer to the diagram below:

 No Confusion With IP NAT Terms: Inside Outside Local Global
For any packet that is transmitted between pc0 and pc1:

when it is being transimitted on the local network, it has ip addresses 1: 192.168.1.2 and 2: 202.1.1.2
(Imagine you are looking at the packet which is being transmitted on the cable between pc0 and the router, you can see these 2 ip addresses in the packet)

when it is being transimitted on the global network, it has ip addresses 3: 202.1.1.1 and 4: 202.1.1.2
(Imagine you are looking at the packet which is being transmitted on the cable between pc1 and the router, you can see these 2 ip addresses in the packet)

Now , let’s give these ip addresses names:

For ip 1: 192.168.1.2
what is the location of packet ? Local
what is the location of device ? device is pc0, location is Inside
so it is Inside Local
Interpret like this: Inside device’s Locally viewed address

For ip 2: 202.1.1.2
what is the location of packet ? Local
what is the location of device ? device is pc1, location is Outside
so it is Outside Local
Interpret like this: Outside device’s Locally viewed address

For ip 3: 202.1.1.1
what is the location of packet ? global
what is the location of device ? device is pc0 (not the router, because this address stands for pc0), location is Inside
so it is Inside Global
Interpret like this: Inside device’s Globally viewed address

For ip 4: 202.1.1.2
what is the location of packet ? global
what is the location of device ? device is pc1, location is Outside
so it is Outside Global
Interpret like this: Outside device’s Globally viewed address

You can verify the above theory with the output below:

 No Confusion With IP NAT Terms: Inside Outside Local Global

By David Rupu Xiao CCIE #24177

One comment

  • Rajesh Kumar Gupta
    May 18, 2012 - 11:15 am | Permalink

    very very good explaination

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