Usable Subnets Usable Hosts Usable Hosts

Number of usable subnets = two to the power of the assigned subnet bits,or borrowed bits, minus two.
– 2power of borrowed bits - 2 = usable subnets
• Borrow 3 bits: 23 -2 = 6 usable subnets
• Borrow 4 bits: 24 -2 = 14 usable subnets
• Borrow 5 bits: 25 -2 = 30 usable subnets
• Borrow 6 bits: 26 -2 = 62 usable subnetsNumber of usable hosts = two to the power of the bits remaining,
minus two (reserved addresses for subnet id and subnet broadcast).
2 x power of remaining host bits - 2 =
usable hosts
– 3 bits borrowed, leaves 25 - 2 = 30 hosts
– 4 bits borrowed, leaves 24 - 2 = 14 hosts
– 5 bits borrowed, leaves 23 -2 = 6 hosts

– 6 bits borrowed, leaves 22 -2 = 2 hostsSubnet Practice: Borrow 3 bitsSubnet # Subnet ID Host Range