Understanding IP Address Allocation
¿What is CIDR (Classless Inter-Domain Routing)?
CIDR is the modern method of allocating IP addresses and routing IP packets efficiently across the internet. Learn how CIDR works, why it matters, and how it affects IP trading and subnet pricing.
- Efficient IP Allocation
CIDR allows precise allocation of IP addresses, avoiding the waste of addresses that occurred with the old class-based system.
- Scalability
It supports hierarchical routing, which improves the scalability of internet routing by aggregating routes and reducing the size of global routing tables.
- Flexibility for ISPs and Enterprises
CIDR enables organizations to request and manage IP space based on actual usage, which is especially useful for Internet Service Providers and data centers.
- Cost Optimization
By acquiring only the number of IPs truly needed, companies can reduce costs and plan for future growth more strategically.
¿What Is CIDR?
CIDR (Classless Inter-Domain Routing) is a method introduced in 1993 to replace the older class-based IP addressing system (Class A, B, C). CIDR allows for flexible IP allocation and more efficient routing by using variable-length subnet masking (VLSM).
CIDR Notation Explained
CIDR notation uses a format like 192.168.0.0/24, where the number after the slash indicates how many bits are used for the network prefix. For example:
- /24 = 256 IP addresses
- /25 = 128 IP addresses
- /26 = 64 IP addresses
- ...and so on.
This notation is essential when buying, selling, or managing IP address blocks.
Why CIDR Matters in IP Trading
In the IP address marketplace, understanding CIDR is crucial. Prices vary depending on the size of the subnet (the lower the prefix, the higher the number of IPs). Buyers and sellers negotiate based on CIDR blocks, and registries such as ARIN, RIPE, and APNIC allocate IPs using CIDR notation.
CIDR and IPv4 Scarcity
With the global exhaustion of IPv4 addresses, trading IP blocks has become a lucrative business. CIDR plays a central role in organizing and structuring these transactions, as the value of an IP block directly depends on its CIDR range.
Instead of assigning fixed-size blocks, CIDR enables organizations to receive IP address ranges that more closely match their actual needs. This helps reduce IP address waste and improves routing performance on the global internet.
CIDR Block Size Reference Table
| CIDR Block | Total IPs | Usable IPs* | Typical Use Case |
|---|---|---|---|
| /30 | 4 | 2 | Point-to-Point |
| /29 | 8 | 6 | Small Network |
| /28 | 16 | 14 | Office LAN |
| /27 | 32 | 30 | Medium Office |
| /26 | 64 | 62 | Infrastructure |
| /25 | 128 | 126 | Enterprise |
| /24 | 256 | 254 | Data Center |
| /23 | 512 | 510 | Resellers |
| /22 | 1,024 | 1,022 | ISPs |
| /21 | 2,048 | 2,046 | Cloud / Scale |
| /20 | 4,096 | 4,094 | Large Host |
| /19 | 8,192 | 8,190 | Large ISP |
| /18 | 16,384 | 16,382 | Nationwide ISP |
| /17 | 32,768 | 32,766 | Large Operator |
| /16 | 65,536 | 65,534 | Class B Block |
| /15 | 131,072 | 131,070 | High Demand |
| /14 | 262,144 | 262,142 | Telecom |
| /13 | 524,288 | 524,286 | Global Network |
| /12 | 1,048,576 | 1,048,574 | Government / ISP |
*Usable IPs = Total IPs minus network and broadcast addresses (for IPv4)
FAQs About CIDR and IP Address Blocks
¿Can I choose any CIDR block when buying IPs?
It depends on availability and registry policies. Some ranges are in higher demand and may be more expensive or restricted.
Is CIDR used with IPv6 too
Yes. Although CIDR originated with IPv4, it is also used in IPv6 addressing and routing.
¿How do I know what size CIDR block I need?
That depends on the number of devices or servers you need to assign IPs to. A future calculator on this page will help you estimate that easily.
¿What are the risks of using too large a block?
Wasting IPs, higher costs, and possible issues with registry justification for allocation.
