Classful Subnetting and IPv4 Subnet Masks

Classful Subnetting
  • Very specific subnetting architecture
    • Not used since 1993
    • But still referenced in casual conversation
  • Used as a starting point when subnetting
    • Standard values
The construction of a subnet
  • 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

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