What is CIDR notation?

CIDR (Classless Inter-Domain Routing) represents a subnet mask as a slash followed by the count of network bits (e.g. /24 equals 255.255.255.0, where 24 bits are 1s and 8 bits are 0s).

Why are two IP addresses subtracted from the usable host count on standard subnets?

In standard IPv4 subnets (/0 to /30), the first address is reserved as the Network Identifier and the last address is reserved as the Broadcast Address.

What is a Cisco Wildcard Mask?

A wildcard mask is the bitwise inverse of a subnet mask (e.g. subnet 255.255.255.0 has wildcard 0.0.0.255). It is used in Cisco router Access Control Lists (ACLs) and OSPF configurations.

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