Web Addresses

IP Addresses

As we discussed previously, when we visit web pages in our browser, the browser makes a HTTP or HTTPS request against the web server for the resource. For this request to be sent to the right server, we must first determine the server’s address. This address takes the form of an Internet Protocol (IP) address. There are currently two ways these IP addresses are specified, IPv4 and IPv6. An IPv4 address consists of 32 bits split into 8 bit chunks, and is typically expressed as four integers between 0 and 255 separated by periods. For example, the IP address for Kansas State University is:

129.130.200.56

Consider that an IPv4 address consists of 32 bits. This means we can represent 2^{32} unique values, or 4,294,967,296 different addresses. You can see how many websites are currently online at https://www.internetlivestats.com/watch/websites/ , as of this writing it was nearly 2 million. Combine that with the fact that every computer connecting to the interent, not just those hosting, must have an ip address, and you can see that we are running out of possible addresses.

This is the issue that IPv6 was created to counter. IPv6 addresses are 128 bits, so we can represent 2^{128} different values, or 340,282,366,920,938,463,463,374,607,431,768,211,456 possible addresses (quite a few more than IPv4)! An IPv6 address is typically expressed as eight groups of four hexidecimal digits, each representing 16 bits. For example, Google’s IPv6 address is:

2607:f8b0:4000:813::200e

IPv6 adoption requires changes to the internet infrastructure as well as all connected machines, and is typically done on a volunteer basis. Thus, it is a gradual process. The United States is at rougly a 47% adoption level; you can see current adoption statistics for all countries at Akamai’s IPv6 Adoption Tool .

Ports

In addition to the address, requests are sent to a port, a specific communication endpoint for the computer. Different applications “listen” at specific ports on your computer - this allows your computer to have multiple applications communicating across the network or interent at the same time. You might think of your computer as an apartment complex; the IP address is its street address, and the ports are individual apartment numbers. Different applications then live in different apartments. Many of these ports are unused (the apartments are vacant), as most computers are only running a few network-facing applications at any given time.

Many applications and communication services have a “default” port they are expected to use. This makes it easy to connect to a remote computer. For example, a webserver uses port 80 by default for HTTP requests, and port 433 for HTTPS requests. If your server is listening at these ports, there is no need to specify the port number in HTTP/HTTPS requests targeting your IP address. You can also run a program on a non-standard port. For example, with our Razor Page applications, we have typically been running our debug version on port 44344 (with IIS Express) or 5001 (when running as a console application). If you know the IP address of your computer, you can visit your running debug server by using the address http://[ip address]:[port] from another computer on your network.

Some of the most common services and thier associated default ports are:

PortProtocolUse
22 Secure Shell (ssh) Used to communicate between computers via a comand line interface
25 Simple Mail Transfer Protocol (SMTP) A common email routing protocol
53 Domain Name System (DNS) Service IP lookup by domain name
80 Hyper-Text Transfer Protocol (HTTP) Servicing WWW requests
143 Post Office Protocol (POP) Retrieving email
143 Interent Message Access Protocol (IMAP) Managing email
193 Interent Relay Chat (IRC) Chat messages
443 Secure Hyper-Text Transfer Protocol (HTTPS) Servicing secure WWW requests

Domain Names

Of course, you don’t normally type 129.130.200.56 into your browser to visit K-State’s website. Instead, you type k-state.edu or ksu.edu, which are domain names owned by the university. A Domain Name is simply a human-readable name that maps to an IP address. This mapping is accomplished by the Domain Name System (DNS), a lookup service composed of a hierarchial network of servers, with the root servers maintained by the Internet Corporation for Assigned Names and Numbers (ICANN).

When you enter a domain name into your browser, it requests the corresponding IP address from its local DNS server (typically maintained by your ISP). If it does not know it, this server can make a request against the broader DNS system. If a matching IP address exists, it is returned to the local DNS server and through that server, your browser. Then your browser makes the request using the supplied IP address. Your browser, as well as your local DNS server, cache these mappings to minimize the amount of requests made against the DNS system.

To get a domain name, you must purchase it from a domain name reseller. These resellers work with ICANN to establish ownership of specific domain names - each domain name can have only one owner, and map to an IP address. Once you’ve purchased your domain name (which is actually leased on an annual basis), you work with the reseller to target the domain name at your preferred IP address(es). This entire process is typically handled through a web application.

Info

The localhost domain name is a special loopback domain. It always points at IP address 127.0.0.1, which is always the local machine (i.e. the computer you are using).