What is really your IP address on the internet?

February 2nd, 2012

I would venture to guess that most folks don’t know their external, public “hide” IP address.  The way the internet works for every site you visit is that they have an actual “public” address on the internet that looks like an address of xxx.xxx.xxx.xxx.   Their public address is a unique in the world.  No one else has that address.  All but the largest internet sites generally have only one address.   Then they have some sort of firewall.  The firewall does something called NAT (Network Address Translation).    The firewall then creates a completely different “private” set of addresses inside the network.   Inside your network every device requires a unique address.  It is easy to tell the difference between a private and a public address.  Anything that is 192.168.x.x, 172.16.x.x, or 10.x.x.x is a private address.  Everything else is a public address.

What happens is if someone looks as you say from a web page such as www.cnn.com they would see your “hide” address as your public address - regardless of what computer you were sitting at behind the firewall.  The firewall with the NAT connects the dots between the external, public address and your unique, internal private address.   In fact everyone in the office would show the same hide address to the public even though you all have separate private addresses.  The firewall just figures out all the traffic.

On the public side there are two ways to address.  One is DHCP (dynamic host control protocol).  DHCP is the traffic cop that temporarily assigns addresses to be used.  The length of time the address is active is called a lease.   This is the simplest form of addressing.   The benefit is that is automatic.  The drawback is that we need real addresses for real devices such as mail servers that never move.   Those addresses are a called “static” addresses because they never move.   Businesses and schools generally want static addresses.  For some ISPs static addresses cost more.

Often cloud based subscription services want to actually know what static internet address your users are coming from so that they can automatically allow them access without complicated login procedures.

https://whatismyip.com will tell you what the external hide address is of the station you are on.  That is the address these vendors are looking to get from you.  That is your true address on the internet.




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