Transport layer services

Question 1

What is port 80?

Answer 1

HTTP

Question 2

What is port 443?

Answer 2

HTTPS

Question 3

What is port 21?

Answer 3

FTP - control

Question 4

What is port 20?

Answer 4

FTP - Data

Question 5

What is port 22?

Answer 5

SSH (secure shell)

Question 6

What is port 23?

Answer 6

Telnet. Used for communication systems and remote maintenance of routers and switches

Question 7

What is port 25?

Answer 7

SMTP (simple mail transfer protocol)
Used to send and receive email. But due to spam and DDoS attacks, it’s now mainly used to transfer emails from one server to another.

Other SMTP ports are; 465, 587 and 2525. 587 being the preferred one as it offers better authentication and more easily identifiable traffic. Making it more secure.

Question 8

What is port 53?

Answer 8

DNS (domain name system) to get ip address from a domain name like www.google.com. The DNS server would get the IP address for the Google server and send it back to the host. Then the data packet would be encapsulated with the destination IP address of the Google server and port 80 of the server to access its HTTP web file, then a session is created by the TCP protocol to continue communication between Host and Web server.

Question 9

What is port 67?

Answer 9

DHCP server (Dynamic Host Configuration Protocol) the protocol used to assign private IP addresses and subnet masks and default gateway to hosts on that network.

Port 67 is the server for this protocol. So it creates and manages this service.

Question 10

What is port 68?

Answer 10

DHCP client. The recipient of the DHCP configuration. Receiving IP address etc from the DHCP servers port 67

Question 11

What is port 69?

Answer 11

TFTP - Trivial File Transfer Protocol. Similar to FTP but not as secure. Used for saving router configurations, and downloading an Operating System.
It is faster but has no authentication so should only be used for transferring files within the Local Area Network

Question 12

What is a socket and socket pair?

Answer 12

A socket is the IP address and Port number in a data packet(aka segment)

A socket pair is both the source and destination IP addresses and Ports on the data packet

Question 13

What is the “netstat” command line used for?

Answer 13

Netstat command on the terminal displays all the TCP connections with ports from Host machine and port to what web address or IP address plus the protocol being transmitted like HTTP

When used with the “-n” option you can receive the numerical values of for example the IP address and Port number instead of the website address and the protocol name(like HTTP)