CIDR (Classless Inter-Domain Routing)
Understanding CIDR: How It Works and Why It Matters
What is CIDR?
The CIDR was introduced in 1993.CIDR (Classless Inter-Domain Routing) is a method of assigning IP addresses that improves the efficiency of address distribution and replaces the previous system based on Class A, Class B, and Class C networks. The initial goal of CIDR was to decrease the rapid exhaustion of IPv4 addresses by slowing the increase of routing tables on routers across the internet. As a result, the number of available internet addresses has greatly increased.
The original classful network design of the internet included inefficiencies that drained the pool of unassigned IPv4 addresses faster than necessary. The classful design included the following:
Class A, with over 16 million identifiers.
Class B, with 65,535 identifiers.
Class C, with 254 host identifiers.
For Example:
If an organization needed more than 254 host machines, it was switched to Class B. However, this potentially wasted over 60,000 hosts if the business didn't need to use them, thus unnecessarily decreasing the availability of IPv4 addresses than CIDR has come to fix this problem.
CIDR addresses are made up of two sets of numbers:
Prefix. The prefix is the binary representation of the network address, which is similar to what is seen in a normal IP address.
- Suffix. The suffix declares the total number of bits in the entire address.
For example, CIDR notation might look like: 192.168.129.23/24 -- with 24 being the number of bits in the address. so it will represent the Class C category. IPv4 addresses support a maximum of 32 bits.
The binary representation IPv4 network addresses, the 32-bit address is broken into four groups of 8 bits each -- called a dotted quad of numbers. A dotted quad looks like
In decimal form: 192.168.0.0.
In Binary form: 11000000.10101000.00000000.00000000.
The same CIDR notation can be applied to IPv6 addresses. The only difference is IPv6 addresses can contain up to 128 bits.
Advantages of CIDR
CIDR reduced the problem of wasted IPv4 address space without causing an explosion in the number of entries in a routing table.
CIDR also enables one routing table entry for a supernet to represent an aggregation of networks -- about which only a router closer to the destination needs to know the details.
CIDR transmits data quickly by enabling routers to organize IP addresses into multiple subnets.