Computer ports are virtual points where network connections begin plus end on computers. A computer’s operating system manages ports, which are software-based.
Computer ports are associated with specific processes or services.
Despite reaching a computer over the same Internet connection, emails go to a different port than webpages, for example.
Port numbers — what are they?
Each port on a network-connected device has a standardized number.
Port 80 is reserved for Hypertext Transfer Protocol (HTTP) messages, for instance.
Unlike IP addresses, port numbers are used to target specific services or applications within specific devices.
What are the benefits of ports for network connections?
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The same network connection can be used to transmit and receive a wide variety of data types. Data is processed by computer ports.
Let’s say Bob sends Alice an MP3 audio recording via File Transfer Protocol (FTP).
Alice’s email application would not be able to interpret MP3 file data passed by her computer.
The file is transferred and stored by Alice’s computer because Bob’s file transfer uses port 21 for FTP.
Although the MP3 sound file and the HTTP webpage files flow to Alice’s computer or laptop over the same Wi-Fi connection, her computer can simultaneously load HTTP webpages on port 80.
Network layers include ports?
As a conceptual model, the OSI model describes how the Internet works.
There are seven layers that divide different Internet services and processes.
The layers are as follows:
Computer Ports are part of the transport layer.
In order to determine which port a packet should go to, a transport protocol such as Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) must be used.
Port numbers are indicated in TCP and UDP headers (see pic above). In a network connection, protocols at the network layer, such as the Internet Protocol (IP), do not know what port is being used.
It is not possible to specify which port a data packet should be sent to in a standard IP header. This is because a port number at a destination IP address is not indicated in IP headers.
Network layer protocols are almost always used in conjunction with transport layer protocols, so the inability to indicate the port at the network layer has no effect on networking processes.
It does, however, impact the functionality of testing software, which uses Internet Control Message Protocol (ICMP) packets to “ping” IP addresses (Great for gaming computers especially as the lower the ping the smoother the online gameplay, something we enhance for all our customers).
ICMP is a network layer protocol that can ping networked devices, but network administrators are unable to test specific services within those devices without access to specific ports.
My Traceroute, for example, offers the option of sending UDP packets with ping software. As opposed to ICMP, which cannot specify a port, UDP can specify a particular port.
A network administrator can test specific computer or server ports within a networked device by adding a UDP header to ICMP packets.
What causes firewalls to block certain ports sometimes?
Using a set of security rules, a firewall blocks or allows network traffic.
An Internet firewall usually sits between a trusted network and an untrusted network.
To protect their networks from online threats, office networks often use firewalls.
Malicious traffic is sometimes sent to random ports, hoping that they will be able to receive it when those ports are left open.
It is similar to a car thief walking down the street and trying to open the doors of parked cars.
As a result, firewalls should be configured to block most of the available ports. A vast majority of the available ports are not legitimately used.
By default, properly configured firewalls block traffic to all computer ports except a few known to be commonly used ports.
In a corporate firewall, the only ports that could be left open are 25 (email), 80 (web traffic), and 443 (web traffic), allowing internal employees to access these essential services, while blocking the remaining 65,000+ ports.
For example, attackers sometimes send attack traffic to port 3389 to exploit vulnerabilities in the RDP protocol.
Port 3389 is usually blocked by default by a firewall in order to prevent these attacks.
Best Computer Repair Tip: As an added layer of protection, always use a VPN either in your router or by using software here
Since remote desktop connections are the only use of this port, such a rule would have little impact on day-to-day business operations, so again it’s typically blocked completely.
How do port numbers differ?
Don’t worry, we know a little about ports over our sister company Top Level Traffic too, with our enhanced invite only digital platform for web design in Bridgend.
Combine that with our 25 plus years of cybersecurity in the IT sector both with server management along with cybersecurity mitigation combined with web design, you can easily see why we are at the top level.
A total of 65,535 possible port numbers exist, but not all of them are commonly used. Ports and their associated networking protocols most commonly used include:
- File Transfer Protocol (FTP) is available on ports 20 and 21. FTP is used to transfer files between clients and servers.
- Secure Shell (SSH) is available on port 22. A secure network connection can be created using SSH, one of several tunnelling protocols.
- Simple Mail Transfer Protocol (SMTP) runs on port 25. The SMTP protocol is used for email.
- The Domain Name System (DNS) runs on port 53. Modern Internet users can load websites and apps without memorizing long lists of IP addresses, since DNS matches domain names to machine-readable IP addresses.
- Hypertext Transfer Protocol (HTTP) runs on port 80. World Wide Web is made possible by HTTP.
- The Network Time Protocol (NTP) runs on port 123. Computer clocks must be synced with each other for encryption to work.
- Border Gateway Protocol (BGP) runs on port 179. In order for the Internet to function efficiently, BGP is essential for establishing routes between its large networks (referred to as autonomous systems). IP addresses controlled by autonomous systems are broadcast using BGP.
- HTTP Secure (HTTPS) on port 443. HTTPS is an encrypted and secure version of HTTP. Port 443 is used for all HTTPS web traffic. DNS over HTTPS, for example, uses HTTPS for encryption.
- The Internet Security Association and Key Management Protocol (ISAKMP) is accessible on port 500. Secure IPsec connections require this step as part of the setup process.
- Remote Desktop Protocol (RDP) uses port 3389. Users can connect remotely to their desktop computers using RDP.
Port numbers and protocols assigned to them are maintained by the Internet Assigned Numbers Authority (IANA).
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