NAT ... Terms confusing me horribly ...

Emissary_of_Pain

Hey all ...

So i recently started the WANs and have reached the NAT section ... they are explained so horribly and are confusing me to the point of pulling my hair out ...

Is there a simple way to explain the terms

Inside
Outside
Inside Local
Inside Global
Outside Local


What is the best way to remember and understand these terms ... (starting to understand why many say WANs are the worst part to study)


All information would be greatly GREATLY appreciated.
Regards,
Richard.

Hatch1921

Have a look at Dan's videos... should be helpful.

https://www.youtube.com/user/danscourses/videos?flow=grid&view=1

Hatch

atorven

Just do a quick search on the forums, others have covered these terms more eloquently.

Zartanasaurus

Inside and outside is relative to the observer.

So you have a bunch of PCs on your internal network. You're using the private range 172.16.1.0/24 internally. Well you can't just use the internet like that because your source IPs aren't public and hosts on the outside won't be able to send replies. So you have NAT configured on the firewall or router. You have an external IP of 1.1.1.1. That's a public IP that can be reached over the internet. Now with the NAT being performed (PAT or NAT overload in this example), hosts in your internal network have their 172 addresses converted to 1.1.1.1 for the outside world to reach. And for instance you do a DNS query to one of google's servers at 8.8.8.8.

172.16.1.0/24 = inside local
1.1.1.1 = inside global
8.8.8.8 = outside global

Inside = your addresses
Outside = someone else's addresses

Local = Addresses as seen from the inside
Global = Addresses as seen from the outside

So what is outside local? If, for some reason, you decided to translate 8.8.8.8 to an inside address on the 172.16.1.0/24 network, that'd be an outside local address. It's someone else's network, but it's being translated into something else and "seen" differently on the internal network.

And I always conclude this by saying "one man's inside global is another man's outside global". Your 1.1.1.1 is an outside global from the PoV of another network.

Lamplight

That was a brilliant explanation, Zart!

I like the "one man's inside global is another man's outside global".

Bose4me

In my own words, this is how I differentiate one from the other...

anything local = private
anything global = public

Private Addresses (local)

Inside local = client/host with a private IP address "native"
Outside local = the private address that sits on the NAT router/switch

Public Addresses (global)

Inside global = the NAT router/switch public address (sits opposite of outside local)
Outside global = "native" address to the public server or Internet address

networker050184

Local are not always private and global are not always public. You are just going to confuse things even more looking at it that way.

Futura

A great philosopher on tech-exams once said.

not sure who it was.,

If its inside of your control then its inside local or global,

If its outside of your control then its outside local or global,


easy to remember.

Emissary_of_Pain

Thanks for all the replies and sorry for my late reply (been traveling a lot)


I think I understand now ... I am definitely going to have to put a lot more time into this section ...

Luckily I got Packet Tracer and can practice setting up routers/nats and hopefully that will help me learn the differences easier