Classless Inter-Domain Routing (CIDR)

What is CIDR?
Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and routing IP packets. CIDR is a replacement for the older system based on classes A, B, and C. A single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number.
Why is CIDR important?
CIDR helps in the efficient allocation of IP addresses. It reduces the load on the internet's routing tables and makes the internet run smoothly by delaying the inevitable exhaustion of IPv4 addresses.
How does CIDR work?
In CIDR, an IP network is represented by a prefix, which is an IP address and some indication of the length of the mask. The mask is often expressed as a slash followed by a two-digit number. This number tells how many of the leftmost contiguous bits of the address comprise the network part.
Exam Tips: Answering Questions on CIDR
Understanding the CIDR notation is crucial for the CompTIA Network+ certification exam. Remember that the number after the slash represents the number of contiguous network bits, which define the network to which the IP address belongs. This number can range from 0 to 32. You can also expect questions that ask you to identify the correct use of CIDR notation or to provide the correct CIDR notation for a given IP address range. Practice interpreting CIDR notation and calculating the number of IP addresses in a given CIDR block to build your proficiency with this concept.