Chapter

1: Given the following host address and subnet mask combinations, determine the subnet address and broadcast addresses:

A: Performing a logical AND reveals the following:

• Subnet 131.18.1.0 and broadcast address 131.108.1.255

• Subnet 151.108.100.0 and broadcast address 151.108.1.127

• Subnet 171.199.100.0 and broadcast address 171.199.100.31

• Subnet 161.88.40.0 and broadcast address 161.88.40.63

2: Given the network 141.56.80.0 and a subnet mask of 255.255.254.0, how many hosts are available on this subnet?

A: Using the formula 2n-2 = 29-2 = 512 hosts, the subnet mask 255.255.254.0 borrows nine (or n) bits from the subnet mask.

3: What is the broadcast address for the subnet 131.45.1.0/24?

A: The broadcast address is 131.145.1.255 where 255 represents all binary 1s.

4: What is the purpose of the broadcast address in any given subnet?

A: The main purpose of a broadcast address in the case of IP is to send out onto the wire a packet that all hosts common to the particular subnets will see and receive. Cisco routers drop broadcasts unless you configure bridging.

5: Given the subnet in binary notation 1111111.11111111.00000000.00000000, what is the decimal equivalent?

A: The decimal equivalent is 255.255.0.0, or a Class B address.

6: Which routing protocols support VLSM and why?

A: RIPv2, OSPF, IS-IS, EIGRP, and BGP. These routing protocols support VLSM because the routing protocols send the subnet mask as part of any routing update.

7: Which routing protocols do not support VLSM?

A: IGRP and RIP I. The only way to overcome this is to use a combination of static IP routes or a default route.

8: Which subnet mask provides approximately 1022 hosts?

A: 2n-2 = 1022, or 2n = 1024. The number of bits required in the subnet mask is 10 bits, or the subnet mask 255.255.252.0 (1111111.11111111.11111100.00000000)

9: What is the equivalent subnet mask for the notation 131.108.1.0/24?

A: The slash notation is common in today's documentation and on Cisco IOS, the slash bit notation represents the number of bits assigned to the subnet mask: /24 means 24 bits. In binary this is 11111111.11111111.11111111.00000000 or 255.255.255.0.

10: Identify the private address ranges defined in RFC 1918?

A: RFC 1918 defines three major classes for private use, which are address ranges that are not routable in the Internet. The following are the three private ranges:

It is common in large organizations to utilize the private Class A address and use public addresses only on the Internet connection using Network Address Translation (NAT).

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