Searching for "subnets"

Q:

You have a Class B network and need 29 subnets. What is your mask?

Answer

A default Class B is 255.255.0.0. A Class B 255.255.255.0 mask is 256 subnets, each with 254 hosts. We need fewer subnets. If we used 255.255.240. 0, this provides 16 subnets. Let's add one more subnet bit. 255.255.248.0. This is 5 bits of subnetting, which provides 32 subnets. This is our best answer A/21

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Subject: CCNA

Q:

Which configuration command must be in effect to allow the use of 8 subnets if the Class C subnet mask is 255.255.25.224?

A) Router(config)#ip classless B) Router(config)#ip version 6
C) Router(config)#ip unnumbered D) Router(config)#ip subnet-zero
 
Answer & Explanation Answer: D) Router(config)#ip subnet-zero

Explanation:

A Class C subnet mask of 255.255.255.224 is 3 bits on and 5 bits off (11100000) and provides 8 subnets, each with 30 hosts. However, if the command ip subnet-zero is not used, then only 6 subnets would be available for use.

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Q:

You need to subnet a network that has 5 subnets, each wit at least 16 hosts. Which classful subnet mask would you use?

A) 255.255.255.192 B) 255.255.255.224
C) 255.255.255.240 D) 255.255.255.248
 
Answer & Explanation Answer: B) 255.255.255.224

Explanation:

You need 5 subnets, each with at least 16 hosts. The mask 255.255.255.240 provides 16 subnets with 14 hosts - this will not work. The mask 255.255.255.224 provides 8 subnets, each with 30 hosts. This is the best answer.

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Q:

The network address of 172.16.0.0/19 provides how many subnets and hosts?

A) 7 subnets, 2046 hosts each B) 7 subnets, 8190 hosts each
C) 8 subnets, 2046 hosts each D) 8 subnets, 8190 hosts each
 
Answer & Explanation Answer: D) 8 subnets, 8190 hosts each

Explanation:

A CIDR address of/19 is 255.255.224.0. This is a Class B address, so that is only 3 subnet bits, but it provides 13 host bits, or 8 subnets, each with 8,190 hosts.

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Q:

The network with ip address 192.168.100.0/27 is to be used on a router. If ip subnet-zero is configured, which statement describe the resulting number of available subnets and hosts?

A) 7 usable subnets, each with 32 host addresses B) 8 usable subnets, each with 30 host addresses
C) 8 usable subnets, each with 27 host addresses D) 7 usable subnets, each with 24 host addresses
 
Answer & Explanation Answer: B) 8 usable subnets, each with 30 host addresses

Explanation:

Because subnet zero is configured and we have a class C address (192.168.100.0) then the network portion will have 3 bits so 8 subnets will be available. The rest of the bits, 5, represent the available hosts, so 2^5=32, but only 30 are available, 0 ad 31 are network and broadcast respectively.

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Q:

Given the following network range 192.168.0.0/24. We want minimum 50 hosts on each of the available subnets. What will be the subnet mask?

A) /24 B) /25
C) /26 D) /27
 
Answer & Explanation Answer: C) /26

Explanation:

Explanation: 50 hosts require 6 bits of the last octet giving us 64 -2 = 62 possible hosts this satisfies our requirement and leaves us 2 bits over for the subnets. The default mask is /24 or 255.255.255.0 adding the 2 bits for the subnets it becomes 255.255.255.192 or /26

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Filed Under: CCENT