Common TCP and UDP port numbers for A+ Core 1

Try 3 questions on this

Pick an answer to see why each option is right or wrong.

1. A technician captures traffic between a workstation and an FTP server that uses its default ports. The user logs in, then requests a directory listing, and the server returns the list of file names. Which of the following server ports carries that list of file names?

   Right. In the game that’s Renown for your Networking building.

   Not that one: B is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   Your answerA.Port 21Port 21 carries the user's commands and the server's short replies. RFC 959 sends the directory listing itself over the separate data connection, so it does not travel on port 21.The answerB.Port 20FTP keeps commands and data apart. RFC 959 says the LIST command's output is transferred over the data connection, not the control connection, and the server's default data port is the one adjacent to the control port.Your answerC.Port 22Confuses FTP with SSH, the secure remote shell protocol that also underlies secure file transfer tools.Your answerD.Port 23Port 23 is registered to Telnet. FTP's command channel borrows Telnet conventions but runs on port 21, and file data never uses port 23.

   Show the full explanation and doc quotes

   IANA registers that default data port, ftp-data, as port 20.

   Written from www.iana.org/assignments/service-names-port-numbers/

2. A branch office's secondary DNS server must copy every record in the organization's zone from the primary DNS server at headquarters. The firewall between the two sites blocks all traffic by default. Which of the following must the technician allow for the copy to succeed?

   Right. In the game that’s Renown for your Networking building.

   Not that one: A is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   The answerA.TCP port 53Copying a whole zone to a secondary server is a zone transfer. RFC 1035 says UDP is not acceptable for zone transfers, which must use reliable connections, and that name servers accept TCP on port 53.Your answerB.UDP port 53UDP port 53 carries ordinary queries, but RFC 1035 says UDP is not acceptable for zone transfers. The secondary server needs TCP port 53.Your answerC.TCP port 445IANA registers port 445 as Microsoft-DS, the port the objectives give SMB. DNS servers do not copy zones over file sharing.Your answerD.TCP port 389IANA registers port 389 for LDAP, a directory protocol. A DNS zone transfer uses the domain service on TCP port 53.

   Show the full explanation and doc quotes

   IANA registers the domain service on TCP port 53, so the firewall must allow TCP port 53.

   Written from www.iana.org/assignments/service-names-port-numbers/

3. A technician capturing traffic from a legacy file-sharing setup sees name lookups on UDP port 137, datagrams on UDP port 138 and sessions on TCP port 139. Which of the following protocols uses these ports?

   Right. In the game that’s Renown for your Networking building.

   Not that one: D is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   Your answerA.LDAPIANA registers port 389 to ldap, the Lightweight Directory Access Protocol. Ports 137 to 139 are NetBIOS's.Your answerB.TelnetPicks the legacy remote terminal protocol, whose registered port is 23.Your answerC.DHCPIANA registers ports 67 and 68 to the Bootstrap Protocol server and client, the ports the objectives list for DHCP. Ports 137 to 139 are NetBIOS's.The answerD.NetBIOSIANA's port registry assigns port 137 to the NETBIOS Name Service, 138 to the NETBIOS Datagram Service and 139 to the NETBIOS Session Service. The three ports together belong to NetBIOS over TCP/IP.

   Written from www.iana.org/assignments/service-names-port-numbers/