cidr

A chart describing CIDR subnets

Admins need to understand some basic networking concepts like CIDR. These are needed when working with AntiSpam & Archiving providers. Here is a simple chart describing the CIDR subnets.

In networks larger than a /31, one address is used for the network number, another for the broadcast address, and generally another as the default gateway for routing to other networks. A /29 may cover a range of 8 addresses, but only 5 of them can be used as host endpoints. A /30 has only 1 usable address.