TCP/IP Subnets - CompTIA A+ 220-801: 2.3

Why subnet the network?

The secret behind the IP address

• The IP adress isn't really a single address
• An IP address is a combination of a network ID and a host ID
• The subnet mask determines what part of the IP address is the network and which part is the host
• The subnet mask is just as important as your IP address!

Classful subnetting

• Very specific subnetting architecture
• Not used since 1993
• But still referenced in casual conversation

Subnet classes

Classless subnetting

• CIDR (Classless Inter-Domain Routing)
• Created around 1993
• Removed the restrictions created by classful subnet masks
• "Cider" block notation

 CIDR notation

• 192.168.1.1/24
• Subnet mask of 255.255.255.0
• 192.168.1.0 through 192.168.1.255 (254 hosts per subnet)
• 10.1.0.1/16
• Subnet mask of 255.255.0.0
• 10.1.0.0 through 10.1.255.255 (65,534 addresses per subnet)

• 10.1.0.1/26
• Subnet mask of 255.255.255.192
• 10.1.0.0 through 10.1.0.63 (62 addresses per subnet)

CIDR in action