What is the new Subnet Mask and what is the Increment? - ProProfs Discuss

# What is the new Subnet Mask and what is the Increment? Subnet the Class B IP Address 130.13.0.0 into 500 Subnets.┬а

A. Subnet Mask 255.255.255.0 with an Increment of 2
B. Subnet Mask 255.255.255.192 with an Increment of 128
C. Subnet Mask 255.255.255.128 with an Increment of 128
D. Subnet Mask 255.255.255.128 with an Increment of 64

This question is part of CCNA Subnetting Quiz
Asked by AP_Jake, Last updated: Aug 11, 2020

#### erijosh

Erijosh

C

Subnet Mask 255.255.255.128 with an Increment of 128

Last octet being .10000000 = 128. Block size: 256-128=128. Increment of 128

Borrowing 9 bits in a class B IP results in third octet all being 1, and first bit in fourth octet being 1. Therefore the final subnet mask is: 11111111.11111111.11111111.10000000 or 255.255.255.128 or /25.

#### Michael_

Michael_

Agreed.

Last octet being .10000000 = 128. Block size: 256-128=128. Increment of 128

Borrowing 9 bits in a class B IP results in third octet all being 1, and first bit in fourth octet being 1. Therefore the final subnet mask is: 11111111.11111111.11111111.10000000 or 255.255.255.128 or /25.

#### pinstrypsoldier

Pinstrypsoldier

Agreed. 9 bits needed for 512 subnet (2^9=512). 16 bits available - 9 leaves 7 bits for hosts.2^7=128

Class B has a mask of /16,plus the 9 bits required for networks makes /25 or 255.255.255.128

#### John Smith

John Smith

Subnet Mask 255.255.255.128 with an Increment of 128

130.13.0.0 Need 500 Networks 128 64 32 16 8 4 2 1 . 128 64 32 16 8 4 2 1 0 0 0 0 0 0 0 1 . 1 1 1 1 0 1 0 0 = 500 in binary Need to borrow 9 bits for # of Networks New Subnet Mask = 255.255.11111111.10000000 (255.128) or /25 ^ Increment = 128 2^9 = # of Networks = 512 2^7-2 = # of Hosts per Network = 126 First 5 IP Ranges 130.13.0.0 - 130.13.0.127 13.0.128 13.0.255 13.1.0 13.1.127 13.1.128 13.1.255 13.2.0 13.2.127

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