public IP in local host machine?

[johnyb98]

Hello everybody.

 

Please, I would like your help to make things clear in something I saw about networking.

In specific video (this is part 2/3), he turns auto to a static IP address.

But, as you can see, the static IP he gives locally to the ethernet interface is 199.207.13.45.

How is it possible? As far as I know and read (and here is something I misunderstand), in local networks, you can give a Class A/B/C IPv4 address to an ethernet interface.

199.x.x.x is out of this ranges. 199.x.x.x are refered to public IPs.

 

How is it possible to give 199.207.13.45 (network 199.207.13.x - subnet: 255.255.255.0 as he says), and this works?

 

Thank you for your time!

[porina]

You can assign any IP address you like, and locally speaking it will work. The problems with that only begin when you try to route between networks. Someone outside your network trying to access that public IP will go to the properly assigned system. Also there is a small chance that you might want to access that public system, but get routed to your local one instead. I think you can file it under bad practice and it should be avoided, but there's nothing stopping you from doing it if you really want to.

[johnyb98]

Thanks a lot!

[Aces High]

Were you expecting to see an RFC 1918 address instead (e.g 10.x.x.x 192.168.x.x)?

 

While most individual host devices today will be behind some kind of NAT gateway device either a home router or corporate firewall there is nothing to stop them being directly addressable. Most home gateway devices will be a modem/router combination and in many cases you can turn off the router part by enabling transparent bridge mode (Also called pass through). Don't do this unless you know exactly what you are doing as you will loose internet as soon as it's enabled and may not be able to go back easily.

 

But if you did... this will allow you to assign the public IP address that would go on your routers WAN interface to another device of your choice and it would be fully addressable across the Public Internet!

 

Some ISPs (especially satellite carriers) do place all their customers behind NAT (Carrier-grade NAT ) so no fun allowed there.

 

Once the world is fully IPv6 the End to End Principle will be restored as the creators of the internet intended it to be!