This means that when an ISP or big enterprise wants to get around 4000 IP addresses (as in our example), it will be allocated a specific subnet range with 20-bits on the network portion and 12-bits on the host portion instead of a whole Class B range. The above example means that you can have 2 12 = 4096 available IP addresses for Hosts. Therefore, instead of having for example 16-bits on the network part (by using the old Class B assignment) you can have for example 20-bits on the network part and thus 12-bits of the remaining length for the host part.
The subnet mask is what defines the length of the network and host portions of the IP address. How CIDR is usedĬIDR uses variable length subnet mask (VLSM) which is not based on the hard boundaries of the 3 Classes described above. Thus, around 61,000 IP addresses were wasted. The ISP was allocated a whole Class B range of 65,535 host IPs although they wanted only 4000. Let’s say an ISP wanted to get 4000 IP addresses to assign to its customers. The above was very inefficient and resulted in a lot of wasted IP addresses.
An IP address is divided into a network part (leftmost bits) and a host part (remaining bits after the network part). What is Classless Inter-Domain Routing (CIDR)Īs you know, an IPv4 address consists of 32 bits and is represented as four octets (1 octet=8 bits).
CIDR was invented to facilitate better and more efficient allocation of IP addressing and especially IPv4 addresses which started running out pretty fast when the whole Internet accelerated its pace during the last 2-3 decades.
0 kommentar(er)
