IP Address

Every computer on the internet has an IP address. The most common type of IP address, known as IPv4, is made up of four sets of numbers ranging from 0 to 255.

Port

To handle multiple connections with the same computer, your computer needs a way to distinguish them. This is done by assigning two port numbers, one at each end of the connection.

A connection is then uniquely identified with four pieces of information: (1) local address, (2) local port, (3) remote address, (4) remote port. Valid port numbers are between 1 and 65535.

Other well-known destination ports are:

• 21 – FTP (control connection)
• 22 – SSH
• 23 – Telnet
• 25 – SMTP
• 80 – HTTP
• 110 – POP3
• 143 – IMAP4
• 443 – HTTPS (HTTP over TLS or SSL)
• 1080 – SOCKS proxy

Subnet

• To connect to other computers on the internet, your computer needs to be part of a subnet. Subnets are connected to each other through routers or gateways.
• These routers forward internet traffic between subnets. Your computer must know which subnet it belongs to to communicate with other computers.
• It also needs to know the IP address of the gateway. A subnet is usually a group of consecutive IP addresses. For example, all IP addresses from 11.22.33.0 to 11.22.33.255 can be in a subnet.

References

• Understanding Internet Connections

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