CIDR (Classless Inter-Domain Routing) is a method of IP addressing and routing that allows for more efficient use of IP address space compared to the older classful IP addressing scheme. CIDR enables flexible subnetting and summarization of IP address blocks, which is essential for the efficient allocation of IP addresses on the internet.
Key points about CIDR include:
- Classless Addressing: CIDR eliminates the rigid class-based system (Class A, B, C) and allows IP addresses to be allocated in a more granular and flexible manner.
- Prefix Length: CIDR notation includes a prefix length in the form of “/X” after the IP address, where X represents the number of bits in the network portion of the address. For example, “/24” indicates that the first 24 bits are used for the network, leaving 8 bits for host addresses in IPv4.
- Subnetting: CIDR makes it easy to create subnets of varying sizes within a larger IP address block. Subnet masks can be represented in CIDR notation as well.
- Routing: CIDR is crucial for efficient routing on the internet. It allows routers to summarize multiple IP address blocks into a single route advertisement, reducing the size of routing tables.
- IP Address Conservation: By allowing for variable-length subnet masks, CIDR helps conserve IP addresses by assigning only the necessary number of addresses to a subnet.
- IPv6: CIDR principles are also applied in IPv6, where address space is vast, and efficient allocation is essential.
CIDR has become the standard for IP addressing and routing on the modern internet. It allows for efficient utilization of IP addresses, which is crucial as the number of devices connected to the internet continues to grow.
Key terms in plain language
Open a term for a concise explanation of language used on this page.
Fiber Internet
Internet delivered through strands of glass using light. Fiber commonly supports high capacity, low latency, and strong upload performance, but availability must be confirmed for the exact address.
Broadband
A general term for always-on, high-speed Internet access. Broadband can be delivered over fiber, cable, DSL, fixed wireless, cellular, or satellite networks.
Bandwidth
The amount of data a connection can carry in a given time, usually measured in Mbps or Gbps. More bandwidth supports more users, devices, and simultaneous applications.
Latency
The time it takes data to travel between two points. Lower latency improves voice, video meetings, cloud applications, gaming, and other real-time services.
Dedicated Internet Access (DIA)
A business-grade Internet connection with capacity dedicated to the customer rather than shared in the same way as typical consumer broadband. It often includes symmetrical speeds and an SLA.
SD-WAN
Software-defined wide area networking. It manages multiple connections and chooses paths based on application needs, performance, and policy to improve resilience and control.