IPv6 CIDR Calculator - Calculate IPv6 Range

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About this tool:

Calculate the IPv6 address range. The tool displays the first and last IPv6 address in the subnet mask range, the number of IPv6 addresses in CIDR notation, IPv6 CIDR, and prefix length.

What is CIDR?

CIDR stands for Classless Inter-Domain Routing, is the IP address protocol improves the allocation of the IP addresses. It replaces the old IP address system based on classes A, B, and C. This protocol also helps significantly slow the growth of the routing table.

Development of CIDR

With the Domain Name System (DNS) development, the classful routing system was used for the IP addresses. But soon, internet developers discovered that it included the severe flaw that it lacked scalability. Therefore, the Internet Engineering Task Force (IETF) created the IP standard in 1993. With that, CIDR was created as a system of routing the new IP addresses. These standards were published under the RFC 1518 and RFC 1519. In 2006, a new version of the standard was published as RFC 4632.

Problems with class-based IP addressing

The old system of the IP address came with some inefficiencies that depleted IP addresses faster than it needed. The class-based routing system includes

  • Class A - 8-bit network address and 24-bit host address with more than 16 million IP addresses.
  • Class B - 16-bit network address and 16-bit host address with 65,535 IP addresses.
  • Class C - 24-bit network address and 8-bit host address with 256 IP addresses.

The real problem would occur when an organization required more than 256 host machines and would no longer fall in class C. Rather than it would fall in class B. That means that the organization would have to use the class B license even though they need far less than 65,535 host machines.

Suppose an organization required 2500 hosts. It would be wasting approximately 65000 hosts by having the class B license, which would significantly decrease the availability of IPv4 addresses.

How does CIDR work?

CIDR uses variable-length subnet masking (VLSM) to mask any number of bits instead of 8-bit chunks in a classful system.

The CIDR IP address contains two groups of numbers.

  • The network address is written as a prefix: like a regular IP address (e.g., 2001:0db8:0000:0000:34f4:0000:0000:f3dd). It is used to identify the network or sub-network.
  • The second part is the suffix, indicating how many bits are in the complete address (e.g.,/64).

Collectively, a CIDR IP address would look like the following: 2001:0db8:0000:0000:34f4:0000:0000:f3dd/64

The network prefix is also mentioned as part of the IP address. That varies depending upon the number of bits required. For example, in the above-mentioned CIDR IP address, the first 48 bits are for the network address, 16 for the subnet, while the remaining 64 bits are for client id.

IPv6 CIDR Calculator

CIDR notation is also used for the IPv6 standard, and the syntax is the same. The only difference between the IPv6 and IPv4, that IPv6 addresses contain up to 128 bits, whereas IPv4 includes 32 bits.

To use the IPv6 CIDR calculator. Perform the following steps.

  • Open the tool: IPv6 CIDR To Range Calculator.
  • Enter the IPv6 CIDR. Enter the following CIDR IP address 2001:4860:4860::8888/32
  • The tool will calculate the IP address range based on the IPv6 address and displays the first and last IPv6 address in the subnet mask range, the number of IPv6 addresses in CIDR notation, IPv6 CIDR, and prefix length.