What is an IP Address? How it works

We see where the IP Address packet originates from when it reaches our network. That IP Address determines our decisions.


It was on 1 January 1983 that the internet started. It was then that ARPANET changed from NCP to TCP/IP protocol suite. The eighties then saw a rapid evolution: in 1985, NSF created NSFNET, a network connecting five supercomputers. The NSFNET, based on ARPANET, also created a national backbone service.

The first ISPs saw the light of day in 1987. It was now possible then to ask for a block of your IP Addresses. Your network could then have as many addresses as you like.

8-bit boundaries assigned addresses. Correspondingly, in the end, we had class A or a few huge blocks, class B or some mid-sized blocks, and class C or many small blocks.

There was a range of class E addresses that were unusable. It was reserved for R & D. Today, it is possible to filter packets from these addresses.

Who is the Host?

Not long ago, it could be said that the IP address is the host. In the olden days, you had a public IP address and a host IP address. The IP Address equaled your identity. IP Address was identity.

However, it was not the identity of the user that was equaled. In fact, it equaled the identity of a host on the network. In those days, a host could have had possibly hundreds of users.


The late eighties saw the exponential growth of the internet. It was realized that the class-wise architecture detailed above would not be scalable. There was little utility to the categorization, there being blocks too big or too small.

This lead to the development of a new technology, known as CIDR or Classless Inter-Domain Routing. It allowed routing announcements. It embraced not only 8-bit boundaries but bit boundaries from a/8 to a/24.

How to define an IP Address

There have been arrays of factors affecting our perception of how an IP Address should be defined.

Cloudflare operates an anycast only network. All of our addresses are advertised in all of our locations. If you are into network measurements and do not take anycast into your calculation, you have little idea of how the internet operates.

Our definition:

An IP Address is different things to different people. For our purposes, it is essentially:

  • A registrant’s postal address;
  • A user’s location;
  • Routing aspects: anycast vs. unicast;
  • Services: HTTP, DNS, email, none;
  • History;
“It’s the location!”

Many providers base their decisions on the user’s location. That is perhaps a good thing since this enables you to reach your content faster. But sometimes less than optimization is what you get.

Other irritants include privacy rules, GDPR, and national sovereignty. What is legal in one economy may nevertheless be illegal in another.

Trying to optimize traffic based on location, in Cloudflare’s case, we seek answers:

  • At which PoP (Point of Presence) does the IP Address land?
  • If the preferred PoP is down, then where will it move to?
  • What if the top 4 are down?
  • In case the transit provider collapses, what then?
A reputable address

The identity of an IP Address user is the subject of the research of a vast mass of researchers. Does an IP Address still identifies the device? Network Address Translation is the result of such an analysis.

The Life of IP Address

It is not easy to determine exactly how long an IP Address lives on your device. On paying extra, some users can get a static address. Dynamic address assignments can be yours for half a day. Some addresses are used for roaming. Others are shared.

IP Address as a temporary identifier

There are different values attached to an IP Address by different services. The types and properties are varied. For one in the filtering business, an IP Address is an identifier with temporary precision. It can change! And that helps the internet remain an open place.

IP Addresses are numbers assigned to computer network interfaces. They assist packet transfer. Without IP Addresses, we would be copying data manually from device to device. Emails without IP Addresses are impossible. Ordinary internet access devices use 3.7 billion IPv4 addresses.