Well Known Port Numbers Online Quiz | Computers

Quiz Answer Key and Fun Facts

1. The most basic one of them all. You open your web browser and enter "http://www.funtrivia.com" at its address bar. With which port on the FunTrivia web server are you establishing connection?

Answer: 80

A port is a virtual data connection used by software components to interact. As long as they are inter-connected through a network (such as the Internet), the components in question may reside on different machines which run on different operating systems.

The concept of client-server is an essential part of this networking model (commonly known as TCP/IP). A particular server or service (such as HTTP) opens a Well Known port for incoming traffic from clients that wish to interact with it (TCP port 80). "Surfing to FunTrivia" means that the web client (your browser) is establishing connection with the FunTrivia web server on this port.

When approaching http://www.funtrivia.com, your client sends the request to the default well known HTTP port. If a web server is listening on a non-default port (i.e. not Well Known), you have to explicitly specify it - e.g. http://www.someurl.com:8182 (for port 8182). This holds true for other protocols (or servers) which use a non-default port.

2. You activate the network link on your home PC. In most cases, the link is configured to obtain an IP address from your ISP (Internet Service Provider). When activated, your network link broadcasts a message on port 67. Which protocol does it use?

Answer: DHCP

DHCP stands for Dynamic Host Configuration Protocol.

The basic process is simple - your network link broadcasts a DHCP request destined to UDP port 67 of all links located on its network segment. The DHCP server listens on this port and allocates your link the properties it has requested, e.g. IP address, network mask, default gateway and DNS server. Typically, the DHCP client in your PC expects to receive the information from the DHCP server on UDP port 68.

DHCP is an extension of the BOOTP protocol, which is rarely used nowadays in PC environments. The Well Known ports of BOOTP are the same as DHCP's.

3. Your friend has sent you a link for photos from his latest trip to Israel, which he put on a public FTP site, ftp://ftp.publicftp.com. You have downloaded the photos and enjoyed the wonderful scenery and atmosphere. With which port(s) of the FTP server has your PC interacted to establish the file transfer?

Answer: 21 and 20 or 21 and a random port

21 (TCP) is the Well Known for FTP control, i.e. sending commands such as "get" or "cd" to the FTP server.

In Active FTP mode 20 (TCP) is the Well Known port for the actual transfer of data.
In Passive FTP mode the FTP server is free to allocate a random port outside the Well Known range (i.e. >1023) for the actual transfer of data.

4. When browsing to FunTrivia, you are using a service which translates the name "www.funtrivia.com" to the IP address of the FunTrivia web server. This service uses port 53 (TCP or UDP). What is the name of the service in question?

Answer: DNS

DNS servers are essential components of the Internet's backbone - http://www.funtrivia.com is much more fun than http://75.126.68.186, isn't it?

5. Oops, the FunTrivia website is not responding and you just don't know what happened to it. Time to utilize your knowledge, open a command line and type "ping www.funtrivia.com" to check whether or not the FunTrivia server is alive (FunTrivia does not block ping requests). In that, you have tried to communicate with port 7 of the FunTrivia server.

Answer: False

This question unfolds a very common mix-up.

Ping is part of the ICMP (Internet Control Message Protocol) suite. Just like TCP and UDP, ICMP is a transport protocol (aka layer 4) in its own right, and NOT a service operating under TCP or UDP to which the concept of port apply in the first place.

TCP port 7 is allocated by IANA to the Echo service, which is used to perform a test similar to ping. Echo is obsolete these days, and disabled by default on most systems.

6. Your PC keeps getting out of sync with the correct time of day. Manually adjusting it is so 19th century. Finally, you decide to follow the advice of a friend and hook up your PC to a server which will automatically do the job. The friend tells you it is very easy to remember the port used by this service. It's 123. Which protocol is your PC using to synchronize its clock?

Answer: NTP

NTP (Network Time Protocol) uses UDP port 123. NTP is a complicated protocol, and a very accurate one, much more than its step-brother protocols TIME (port 37) and DAYTIME (port 13). NNTP is Network News Transfer Protocol (port 119) used by newsgroup browsers (in recent years there was a shift to web-based newsreaders).

The US Naval Observatory net of NTP servers is a popular one (http://tycho.usno.navy.mil/ntp.html). You may point your PC to an NTP server of your choice, as long as you obtain an NTP client of course (e.g. starting from Win2K MS distributions come with a built-in NTP client called Windows Time Service).

7. Internet banking cannot use security-agnostic protocols such as HTTP. The Secure HTTP protocol (HTTPS) was developed for such applications which require encrypted transfer of data. Since HTTPS and HTTP are basically similar, the only difference being the added security layer, both have the same Well Known port.

Answer: False

By default, HTTP servers use TCP port 80 while HTTPS servers use TCP port 443.

Indeed, HTTPS is considered more an extension of HTTP than an independent protocol. Essentially, the extension is the secure layer (SSL or TLS).

8. In the past, numerous attacks on home PCs utilized the fact that, by default, some MS Windows services opened certain ports for incoming traffic. One of the most notorious cases is the "NetBIOS trio". Many users have lost their sanity over hacks and exploits on these ports. Which are they?

Answer: 137,138,139

It is still very difficult to neutralize the "NetBIOS trio" on Windows systems, although the NetBIOS services are not really in use (aaargh!). What your ISP should be doing these days is block incoming traffic to these ports before it gets to your PC. Ever thought of verifying this?

By the way, the same goes to ports 445 (Microsoft Directory Service, which replaced NetBIOS in functionality - have a look at http://www.grc.com/port_445.htm) and 135 (EPMAP service, http://www.grc.com/port_135.htm).

9. Developed in the late 60s, this is one of the first standardized Internet protocols. It enables its user to interact with a remote server using a terminal emulator. TCP port 23 is used for the communication between client and server. Which is this protocol?

Answer: Telnet

The glory days of Telnet (Teletype Network) are past, and its gradual dethroning is almost complete. It is still used in localized environments where security is less of an issue (e.g. behind a strong firewall). A basic highlight on Telnet can be found at http://www.telnet.org

10. RTSP (Real Time Streaming Protocol) is a cool framework for a "network VCR remote control unit". Using RTSP you may instruct a remote video streaming server to start, stop, pause or fast-forward a video you have picked. Which is the default port assigned to RTSP?

Answer: 554

By default, RTSP servers use port 554 (TCP or UDP). Important to note that the actual audio/video streaming is implemented by a totally different protocol, always UDP-based (e.g. RTP, RDT), on a different port.

Thanks for taking my quiz, hope you had either a positive learning experience or a reassuring one. If you want to learn more on the subject, two excellent resources are the IANA pages at http://www.iana.org/assignments/port-numbers and the port-specific pages at http://www.grc.com/port_X.htm (where X is the port number you would like to get info on).

Source: Author gentlegiant17

This quiz was reviewed by FunTrivia editor crisw before going online.
Any errors found in FunTrivia content are routinely corrected through our feedback system.

Well Known Port Numbers Trivia Quiz

Knowledge of default port numbers used by the basic Internet services is important and handy even for home users. These "Well Known Port Numbers" (0-1023) are allocated by IANA (Internet Assigned Numbers Authority). So, how well do you know them?

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