Summary of Subnetting

The following IP address is listed in dotted decimal format. What is the corresponding binary value of this IP address?

112.14.12.8

• A. 01100000.00110000.01101111.10110111

• B. 0.11.0.11

• C. 01110000.00001110.00001100.00001000

• D. 01110000.00001110.11000000.00110011

The correct answer is C. The conversion of these binary bits yields a decimal value of 112.14.12.8. Answer A can be identified quickly as incorrect by noting that the fourth octet begins with 1, but its value is not greater than 128. Answer B can be eliminated immediately because it is not in the format of a binary IP address. Answer D can be judged to be incorrect by determining the decimal value of either the third or fourth octet. It is important to note that it is not necessary to convert each one of the possible answers into decimal format. It is much quicker to eliminate the obviously wrong answers (such as B) and then isolate reasons to remove other answers before converting any values.

Which of the following statements is not true concerning the deciphering of a subnet ID from an IP address and subnet mask using the ANDing process?

• A. If the subnet mask and the IP address both have values of 1, the resulting network ID bit is 1.

• B. If the subnet mask has a value of 1 and the IP address has a value of 1, the resulting network ID bit is 0.

• C. If the subnet mask has a value of 1 and the IP address has a value of 0, the resulting network ID bit is 0.

• D. If the subnet mask has a value of 0, the resulting network ID bit is 0.

The correct answer is B. It specifies that a network ID bit of 0 is the result when comparing a subnet mask bit with a value of 1 and an IP address with a value of 1. This is not one of the rules used to decipher network IDs. Therefore, answer B is the correct answer. Answers A, C, and F are the three rules presented in this chapter for deciphering network IDs from an IP address with a subnet mask. Therefore, these answers are incorrect.

Which of the following tools can be utilized to test IP connectivity between two devices? (Choose the three best answers.)

• A. Ping

• B. Telnet

• C. Traceroute

• D. show ip interface

• E. show ip protocol

The correct answers are A, B, and C. Ping, Telnet, and Traceroute are all tools mentioned in this chapter for testing IP connectivity between two devices. Answers D and E are incorrect because show ip interface and show ip protocol are used to monitor IP addresses and the functioning of IP within a local router.

Which of the following tools will identify the address of intermediate hops between two destinations?

• A. Traceroute

• B. Telnet

• C. Ping

• D. Rlogin

• E. TCP

The correct answer is A. The traceroute command can be used to identify the address of every intermediate hop between two locations. Answer B is incorrect because the telnet command is used to obtain remote control of a destination device. Answer C is incorrect because the ping command only tells users whether they have IP connectivity. Answer D is incorrect because rlogin is a command used for remote access on Unix machines. Finally, answer E is incorrect because TCP is a Layer 4 protocol, and it is not used for testing IP connectivity.

Which of the following is the default mask of a class A IP address?

• A. 255.0.0.255

• B. 255.255.0.0

• C. 255.0.0.0

• D. 255.255.255.0

The correct answer is C. Class A addresses have a default mask of 8 bits, or 255.0.0.0. Answer A is incorrect because all default masks are made up of contiguous bits. Answer B is incorrect because 255.255.0.0 is the default mask of a class B IP address, not a class A IP address. Answer D is incorrect because 255.255.255.0 is the default mask of a class C IP address, not a class A IP address.

Which of the following terms does not identify a layer of the TCP/IP model?

• A. Application

• B. Transport

• C. Presentation

• D. Internet

• E. Network access

The correct answer is C. Only the OSI model uses the Presentation layer; therefore, this term does not identify a layer of the TCP/IP model. Answers A, B, D, and E all identify separate layers of the TCP/IP model.

Which of the following services exist at the Application layer of the TCP/IP model? (Choose the best answers.)

• A. SMTP

• B. FTP

• C. ICMP

• D. ARP

• E. TFTP

The correct answers are A, B, and E. SMTP, FTP, and TFTP all exist at the Application layer of the TCP/IP model. Answer C is incorrect because ICMP exists at the Internet layer of the TCP/IP model. Answer D is incorrect because ARP exists at the Internet layer of the TCP/IP model.

If you wanted to locate the hardware address of a local device, which protocol would you use?

• A. ARP

• B. RARP

• C. ICMP

• D. PING

The correct answer is A. If you know the IP address and you are trying to find the hardware (MAC) address, ARP is the choice. Answers C and D are incorrect because a ping command is used to verify network connectivity and sends ICMP packets to determine this. RARP, answer B, is incorrect because it will find the IP address, given the hardware address.

Which of the following services is used to translate hostnames into IP addresses?

• A. SNMP

• B. SMTP

• C. IP

• D. UDP

• E. DNS

The correct answer is E. DNS is used to translate word-based addresses into IP addresses, or vice versa. SNMP and SMTP are TCP/IP Application layer services, but they do not perform address translation. SNMP is used to monitor remote devices, and SMTP is used to send email between devices. IP is not a service but rather a protocol used for logical addressing and routing. Therefore, answers A, B, and C are incorrect. Finally, UDP is a Transport layer protocol used for packet sequencing, which makes answer D incorrect.

Which of the following functions is not performed by TCP?

• A. Flow control

• B. Sequencing

• C. Error checking

• D. Subnetting

The correct answer is D. Subnetting is not a function performed by TCP; it is a process used to create more networks out of classful IP addresses. Answer A is incorrect because TCP does indeed provide flow control in the form of sliding windows and buffer management. Answer B is incorrect because TCP provides sequencing to ensure that datagrams are read in the correct order on the receiving side. Finally, answer C is incorrect because TCP provides error checking by applying a checksum to the TCP header and encapsulated data.