Network Concepts

Which of the following pairs of well-known ports are the default values you would use to configure a POP3 email client?

• 110 and 25

• 143 and 25

• 110 and 143

• 80 and 110

Answer explanation

The default port for the Post Office Protocol (POP3) is 110. The default port for the Simple Mail Transfer Protocol (SMTP), the other protocol used by email clients, is 25. Port 143 is the default for the Internet Message Access Protocol (IMAP), a different email mailbox protocol that clients never use with POP3. Port 80 is the default for the Hypertext Transfer Protocol (HTTP), which is not used by email clients.

Which of the following server applications use two well-known port numbers during a typical transaction?

• NTP

• SNMP

• HTTP

• FTP

Answer explanation

The File Transfer Protocol (FTP) uses two port numbers. It uses the first, port 21, for a control connection that remains open during the entire client/server session. The second port, 20, is for a data connection that opens only when the protocol is actually transferring a file between the client and the server.

Which of the following protocols does the Ping utility use to exchange messages with another system?

• UDP

• TCP

• ICMP

• IGMP

Which of the following components does the port number in a transport layer protocol header identify?

• A transport layer protocol

• An application

• A gateway

• A proxy server

Answer explanation

The port numbers specified in a transport layer protocol header identify the application that generated the data in the packet or the application that will receive the data. Port numbers do not identify transport layer protocols, gateways, or proxy servers.

Which of the following organizations is responsible for assigning the well-known port numbers used in transport layer protocol headers?

• Institute for Electronic and Electrical Engineers (IEEE)

• Internet Assigned Numbers Authority (IANA)

• Internet Engineering Task Force (IETF)

• International Organization for Standardization (ISO)

Answer explanation

The IANA assigns values for well-known port numbers. The IEEE publishes Ethernet standards, among many others. The IETF develops standards for Internet technologies. The ISO developed the Open Systems Interconnection (OSI) model.

A client on a TCP/IP network is attempting to establish a session with a server. Which of the following correctly lists the order of Transmission Control Protocol (TCP) session establishment messages?

• SYN, ACK, SYN, ACK

• SYN, SYN, ACK, ACK

• SYN/ACK, SYN/ACK

• SYN, SYN/ACK, ACK

Answer explanation

The TCP connection establishment exchange is a three-way handshake. The first frame contains a SYN message from the client, the second frame contains a SYN/ACK message from the server, and the last frame contains an ACK message from the client.

Which of the following is the default well-known port number for the Hypertext Transfer Protocol (HTTP) used for web client/server communications?

• 22

• 20

• 80

• 1720

Answer explanation

You owe me pushups if you got this wrong

The secured version of the Hypertext Transfer Protocol (HTTPS) uses a different well-known port from the unsecured version. Which of the following ports is used by HTTPS by default?

• 25

• 80

• 110

• 443

Answer explanation

You owe me pushups if you got this wrong

Which of the following Transmission Control Protocol (TCP) control bits is set to 1 to initiate the termination of a session?

• SYN

• URG

• FIN

• PSH

• END

Answer explanation

The termination phase of a TCP connection begins when either the client or the server sends a message containing the FIN control bit with a value of 1. The other control bits listed have nothing to do with the connection termination procedure, and there is no END bit.

What field in the Transmission Control Protocol (TCP) Option subheader specifies the size of the largest segment a system can receive?

• MSS

• MMS

• Window

• WinMS

Answer explanation

The Maximum Segment Size (MSS) field in the TCP Options subheader specifies the size (in bytes) of the largest segment a system can receive. The Window field indicates the amount of data (in bytes) that the receiver can accept. There are no MMS or WinMS fields in a TCP header.