How do I get unique incoming request IP address

Question

There are four people who are sharing a same wifi connection, according to below definition there IP must be unique.
An IP address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication.

Q1. IS IT SO OR NOT?

For uniquely identifying them I tried:

request.remoteAddress

But I get same IP for those all four person.

Q2.HOW UNIQUELY IDENTIFY THEM?(should I say them to pass some token like thing to identify them uniquely? but I will prefer unique IP)

Answer 1

The correct phrasing is that they all 4 are behinds a NAT firewall -- that is;

• They all have unique IP addresses on their internal network (like 192.168.x.x or other internal IP address) see http://en.wikipedia.org/wiki/Private_network and RFC1918 for details.
• They are connecting to the public internet though a firewall/gateway which does network address translation (see http://en.wikipedia.org/wiki/Network_address_translation for details).

This is the common way for most home/office networks to connect to the internet, for two reasons -- it require much fewer public internet addresses, and it also makes the network more secure as avoiding public addresses for internal resources means that there is less likelyhood for that you fail to configure you firewalls correctly.

The downside is that IP addresses are by no means a unique ID for the users -- that is what Cookies are for.