Understanding IP Block Allocation

Understanding IP Block Allocation

Most hosting firms allocate ‘blocks’ of static IP addresses to their clients, identified by a CIDR notation (such as /29 or /30). Each block represents a particular subnet on the host’s network, and each subnet has its own subnet mask.

In networking, IP addresses consist of two core components: the network address and the host identifier. CIDR notations describe how many bits of the address (there are 32 in total, and each bit can be either 0 or 1) are used for the routing/networking prefix, and by association how many bits are left for host identification. For example, an ip block of /29 signifies that 29 out of the 32 bits are used for routing.

That means you’ve 8 addresses available. It’s worth noting, however, that two are typically used for broadcast and loopback. In some networks, you may also need an additional address for your router’s interface. That leaves a total of five usable addresses.


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