Protcols & Ports

What is a network port?

A logical endpoint used to identify a specific service or application running on a device.

What is a protocol?

A set of rules that defines how devices communicate and exchange data over a network.

What is RDP?

Remote Desktop Protocol (RDP) is a protocol that allows users to remotely access a computer through a graphical desktop interface.

What is the standard port for RDP?

TCP port 3389

How is RDP different from SSH?

RDP provides a graphical desktop interface, while SSH primarily provides a text-based-command-line interface.

Does a service have to run on its standard port?

No. A service can be configured to use a different port.

Why might a web server use port 8080 instead of the standard port 80?

Because applications can be configured to listen on non-standard ports.

How do you specify a non-standard port when connecting to a service?

The port specified after the IP address using a colon, for example:

192.168.1.100:8080.

Does using a non-standard port change the protocol being used?

No. The port number does not determine the protocol itself; a service can use a non-standard port.

What is the TCP three-way handshake?

The process used to establish a TCP connection between a client and the server. It consists of:

• SYN → SYN/ACK → ACK

What happens during the TCP three-way handshake?

1. Client → Server: SYN - requests to establish a TCP connection and start synchronization.

2. Server → Client: SYN/ACK - acknowledges the request and response with its own synchronization.

3. Client → Server: ACK - Acknowledges the server’s response.

• After this, the TCP connection is established.

What does SYN mean in TCP?

SYN (Synchronize) Is used to initiate a TCP connection and synchronize sequence numbers between the two devices.

What does SYN/ACK mean?

SYN/ACK combines synchronization and acknowledgment. The server uses it to acknowledge the clients SYN and send its own SYN.

What does ACK mean in TCP?

ACK (Acknowledgment) confirms that data or a TCP message has been successfully received.

What happens after the TCP connection has been established?

The devices can exchange data, such as the bytes that make up a file or network request.

What does FIN mean in TCP?

FIN (Finish) Is used to properly and gracefully close a TCP connection.

What does RST mean in TCP?

RST (Reset) abruptly terminates a TCP connection, usually because a serious problem has occurred or the connection cannot continue.

What is the difference between FIN and RST?

FIN closes a TCP connection, gratefully and normally.

RST terminates the connection immediately and indicates an abnormal situation.