Implied netmasks of classful addresses

• A classful network has a “natural” or “implied” prefix length or netmask:

  • Class A: prefix length /8 (netmask 255.0.0.0)
  • Class B: prefix length /16 (netmask 255.255.0.0)
  • Class C: prefix length /24 (netmask 255.255.255.0)

• Old routing systems often used implied netmasks

• Modern routing systems always use explicit prefix lengths or netmasks

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