As the firewall administrator, Claire notices a rule that permits traffic to tcp ports 20 and 21 on a range of internal servers. What is the MOST likely reason Claire would have to be suspicious of this rule
-
FTP servers should all be replaced with SFTP servers
-
There should be one specific firewall rule for each FTP server
- FTP is deprecated and should be replaced by TFTP
- It is uncommon to have more than one FTP server(Correct)
Explanation
A small analogy before a formal definition, is always good for better and easy understanding. Agree?
So, suppose that I baked a cake for my friend and send my younger brother to deliver it to her house. For this, he first opens the door of my house, comes out and then takes the route following the address of her house. Again, the door of her house has to be opened before the cake can reach her and she can taste it.
But wait, outside the house, he finds two main doors (one leading to her tenant section), one red and one blue. So, which one is he supposed to knock to reach her directly? How to identify the correct door? If the address given also specified the door colour or a number, it would have been much easier to locate her without possibly bumping into her tenants, right?
Now, we come to Networking scenario.
Here, the houses are analogous to the computers. Me and my friend are analogous to the processes (applications/programs) running on computers. The cake is the message or file that needs to be transferred. My younger brother is the TCP or UDP connection between the two computers using network. The doors are analogous to sockets which are interfaces between application and transport layer in a host. It is important to knock the correct door (socket) for the right delivery of the message.
IP address has been used to reach the destination computer. But now, how to identify the correct socket to reach the destined process? For this, the sockets are assigned special numbers called “Port Numbers” , which help to identify the exact sender and receiver processes (applications/ programs). So, along with IP address, port numbers are also provided and both of these work together to locate the destination computer and then the destined process.
If we look at the TCP and UDP segment structures, we can easily find the “source port number” and “destination port number” fields right at the top of the structures. Port numbers are associated with TCP/IP connections and mainly help in Multiplexing and Demultiplexing data.
For a formal definition, we can say,
“ A port number is the logical address of each application or process that helps in identifying the sender and receiver processes of messages.”
Each port number is a 16-bit number ranging from 0 to 65535.
Well-known Port Numbers :- Port Numbers reserved for use by some popular application protocols.
Example- HTTP has port number 80. FTP has port number 21.
Ephemeral Port Number:- Port numbers assigned temporarily for the duration of its use.
Hope it helps