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.

Asked by AP_Jake, Last updated: Apr 13, 2021

#### erijosh

Erijosh

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