Question 1 | One of the advantages of variable-length subnet masking is the capability to structure your network in hierarchical fashion. Which of the following represents the benefits of hierarchical addressing? (Choose two.) -
A. Reducing the amount of information stored in routing tables -
B. Enabling the use of addressing with discontiguous networks -
C. Allocating IP addresses more efficiently -
D. Allowing for classful routing algorithms |
A1: | Answers A and C are correct. Hierarchical addressing schemes make routing tables smaller and allocate addresses more efficiently. Answer B is incorrect because discontiguous networks are problematic and not an advantage of a hierarchical structure. Answer D is incorrect because, although related , classful algorithms are not a direct benefit of hierarchical addressing schemes. |
Question 2 | Which mechanism would you use to reduce the number of routing table updates generated from implementing a large number of Class C addresses? -
A. VLSM -
B. The ip helper command -
C. CIDR -
D. OSPF |
A2: | Answer C is correct. CIDR reduces the number of updates by allocating a contiguous block of addresses. Answer A is incorrect because VLSM enables you to further subnet a subnetwork. Answer B is incorrect because the ip helper command allows you to break the router rule that prevents the forwarding of broadcast packets. Answer D is incorrect because OSPF is a link-state routing protocol and not necessarily a mechanism for classless IP addressing. |
Question 3 | CIDR is predominantly used in which of the following scenarios? -
A. OSPF only -
B. EIGRP only -
C. Route summarization -
D. Classless routing |
A3: | Answer D is correct. CIDR stands for Classless Interdomain Routing and is predominately used in classless routing scenarios. Answers A and B are incorrect because CIDR can be used with OSPF and EIGRP, among others. Answer C is incorrect because classful protocols also summarize at major network boundaries by default. |
Question 4 | You are presented with an IP address with a prefix of /22. How many more subnets can you add to your design if you further subnet with a VLSM mask of /27? |
A4: | Answer C is correct. 27 bits “ 22 bits = 5 bits. 2 5 = 32 subnetworks gained . Answer A is incorrect because there would need to be 8 bits separating the original subnet bit and the VLSM bit to generate 256 subnets. Answer B is incorrect because there would need to be 6 bits separating the original subnet bit and the VLSM bit to generate 64 subnets. Answer D is incorrect because there would need to be 4 bits separating the original subnet bit and the VLSM bit to generate 16 subnets as opposed to the 5 bits that generate 32 subnets. |
Question 5 | Which one of the following is not an address reserved for private networking according to RFC 1918? -
A. 10.10.255.255 -
B. 172.16.100.0 -
C. 192.168.16.100 -
D. 196.128.10.254 |
A5: | Answer D is correct. 196.128.10.254 is not within a reserved private address range. Answer A is incorrect because it is within the private Class A range of 10.0.0.0 “10.255.255.255. Answer B is incorrect because it is within the private Class B range of 172.16.0.0 “172.31.255.255. Answer C is incorrect because it is within the private Class C range of 192.168.0.0 “192.168.255.255. |
Question 6 | Which formula should be used to determine the number of subnets needed on a Cisco router running Cisco IOS release 12.0 or higher? -
A. n “2 -
B. 2 n “2 -
C. 2 n -
D. 2 n /2 |
A6: | Answer C is correct. The standard formula for subnets now is 2 n subnets available. The all-ones subnet has always been legal according to the RFC, and subnet zero is enabled by default on all Cisco routers with a Cisco IOS release of 12.0 and higher. Answer A is incorrect because the math is simply wrong. Answer B is incorrect because that is the formula for calculating the available hosts . Answer D is incorrect because the math is wrong. |
Question 7 | Which of the following are valid terms relating to the general concept of grouping contiguous classless addresses? (Choose all that apply.) -
A. Supernetting -
B. Subnetting -
C. Aggregation -
D. Summarization |
A7: | Answers A, C, and D are correct. These are all terms related to CIDR and the grouping of classless addresses. Answer B is incorrect because subnetting is the specific process of arbitrarily dividing up networks to provide a more hierarchical routing design. |
Question 8 | Which one of the following prefixes is most often implemented on WAN point-to-point serial links with VLSM? -
A. /16 -
B. /24 -
C. /28 -
D. /30 |
A8: | Answer D is correct. This particular VLSM mask provides for only two hosts, which is perfect for WAN connections. Answer A is incorrect because it is a standard Class B mask of 16 bits of CIDR subnetting. Answer B is incorrect because it is a standard Class C mask of 24 bits of CIDR subnetting. Answer C is incorrect because, although it provides a good subnet for breaking up larger subnets, /30 is the most efficient choice for WAN links. |
Question 9 | Which of the following protocols supports VLSM in a Cisco routing environment? (Choose all that apply.) -
A. Static routing -
B. OSPF -
C. IS-IS -
D. EIGRP -
E. RIPv2 |
A9: | Answers A, B, C, D, and E are correct. Static routing, OSPF, IS-IS, EIGRP, and RIP version 2 all support VLSM. BGP4 also supports VLSM. RIPv1 and IGRP do not support VLSM. |
Question 10 | Which of the following statements relating to VLSM and route summarization are true? (Choose all that apply.) -
A. OSPF must have the no auto-summary entry configured because OSPF automatically summarizes IP networks. -
B. You can only further subnet a subnetwork that is currently unused. -
C. The routing protocol being used must transport the prefix length as well as use a 32-bit address. -
D. To properly implement summarization in a network, the multiple addresses must share similar low-order bits. |
A10: | Answers B and C are correct. You cannot further subnet a network using VLSM if the address space is already in use. Also, VLSM and route summarization demand a 32-bit addressing routing protocol that carries the prefix length (subnet mask information). Answer A is incorrect because EIGRP, not OSPF, must have the no auto-summary entry configured. Answer D is incorrect because the multiple addresses must share similar high-order bits. |