CIDR, or Classless Inter-Domain Routing, is a method for allocating IP addresses and for routing Internet Protocol packets. It was introduced to replace the previous classful IP addressing architecture, allowing for more efficient use of IP address space.
In CIDR notation, an IP address is followed by a slash and a number that indicates the size of the block of addresses. For example, 192.168.1.0/24 represents a block of 256 IP addresses, from 192.168.1.0 to 192.168.1.255. The number after the slash (in this case, 24) is the prefix length, which indicates how many bits of the IP address are fixed.
CIDR allows for more flexible allocation of IP addresses, as it can create blocks of any size, not just the fixed classes (A, B, C) of the older system. This helps in reducing the routing table sizes and improving the scalability of the Internet's routing infrastructure.
For instance, if an organization needs a block of 512 IP addresses, they could be allocated 192.168.0.0/23, which includes addresses from 192.168.0.0 to 192.168.1.255.
In the context of cloud services, Tencent Cloud utilizes CIDR for allocating IP addresses to its cloud resources, enabling efficient network management and routing within its infrastructure.