Classful Subnetting and IPv4 Subnet Masks

Question 1

Classful Subnetting

Answer 1

• Very specific subnetting architecture
  
  • Not used since 1993
  • But still referenced in casual conversation
• Used as a starting point when subnetting
  
  • Standard values

Question 2

The construction of a subnet

Answer 2

• Network address
  
  • The first IP address of a subnet - Set all host bits to 0 (0 decimal)
• First usable host address
  
  • One number higher than the network address

• Network broadcast address
• The last IP address of a subnet - Set all host bits to
1 (255 decimal)

• Last usable host address
  
  • One number lower than the broadcast address

Question 3

CIDR chart

Answer 3

Binary Decimal
00000000 0
10000000 128
11000000 192
11100000 224
11110000 240
11111000 248
11111100 252
11111110 254
11111111 255