Port Numbers Interview Questions & Answers

  1. Question 1. What Is A Port Number?

    Answer :

    A port number is part of the addressing information used to identify the senders and receivers of messages. Port numbers are most commonly used with TCP/IP connections. Home network routers and computer software work with ports and sometimes allow you to configure port number settings. These port numbers allow different applications on the same computer to share network resources simultaneously.

  2. Question 2. What Is The Range Of Ports Or How Many Ports Are There?

    Answer :

    Port numbers can vary from 0 to 65535, so total we can get 65536 ports.

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  4. Question 3. Why Port Numbers Are Just 65536?

    Answer :

    This is because limitation in TCP/IP stacks where the port field is just 16 bit size. So we get only 2^16 port which is equal to 65536 ports.

    Port numbers have a range of 0…65535 (although often 0 has special meaning). In the original BSD TCP implementation, only root can bind to ports 1…1023, and dynamically assigned ports were assigned from the range 1024…5000; the others were available for unprivileged static assignment. These days 1024…5000 is often not enough dynamic ports, and IANA has now officially designated the range 49152…65535 for dynamic port assignment. However even that is not enough dynamic ports for some busy servers, so the range is usually configurable (by an administrator). On modern Linux and Solaris systems (often used as servers), the default dynamic range now starts at 32768. Mac OS X and Windows Vista default to 49152…65535.

  5. Question 4. What Is The Well-known Ports?

    Answer :

    Well known ports are from 0 to 1023(total 2^10=1024 ports).

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  7. Question 5. What Is The Registered Ports, And (range: 1024 To 49151)?

    Answer :

    Used by specific service upon applications such as Oracle database listener (1521), Mysql (3306), Microsoft Terminal server (3389) etc.

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  9. Question 6. What Is The Dynamic And/or Private Ports. (range: 49152 To 65535)?

    Answer :

    These ports can’t be registered by IANA. This is used for custom or temporary purposes and for automatic allocation of short-lived (or ephemeral) ports which is used internally by application/processes. You can see these ports by running ‘netstat’ command under “Local address” column.

  10. Question 7. What Do You Mean By Default Port?

    Answer :

    Default port is a designated port for particular well-known server.

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  12. Question 8. Can We Change Default Port For A Service (example Apache, Squid)?

    Answer :

    Yes, we can change.

  13. Question 9. What Is The Protocol Numbers For Tcp And Udp?

    Answer :

    TCP protocol number:6

    UDP protocol number: 17

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  15. Question 10. How To Find Which Ports Are Open?

    Answer :

    You can find the ports in your linux server with the nmap command:

    #netstat -ntlp

    and n -> display the host by numbers

    t ->shows tcp protocols

    u ->to check udp protocols

    l ->listening ports

    p -> displays which process controls the port