CIDR /2 IPv4 & IPv6 Reference

Understanding CIDR notation for IPv4 and IPv6 subnets

CIDR (Classless Inter-Domain Routing) notation is a compact method for specifying IP addresses and their routing suffix. This page provides detailed information about the /2 subnet.

IPv4 /2 Subnet Details

Extremely large network with millions of hosts. Such large address blocks are typically managed by ISPs or very large corporations and are often subdivided extensively.

IPv4 Subnet Information

CIDR Notation/2
Subnet Mask192.0.0.0
Binary Subnet Mask11000000 00000000 00000000 00000000
Total Addresses1,073,741,824
Usable Hosts (Standard)1,073,741,822
AWS Usable IPs1,073,741,817 (5 reserved)
Azure Usable IPs1,073,741,817 (5 reserved)
GCP Usable IPs1,073,741,818 (4 reserved)

IPv6 /2 Subnet Details

Large allocation typically used by regional registries or major ISPs

IPv6 uses a 128-bit address space, a massive increase from IPv4's 32 bits. This allows for approximately 340 undecillion (3.4 x 1038) unique addresses, effectively eliminating the address exhaustion concerns of IPv4.

IPv6 addresses are represented as eight groups of four hexadecimal digits, separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Leading zeros in each group can be omitted, and one sequence of consecutive all-zero groups can be replaced by a double colon (::), for instance 2001:db8::1.

Key Differences from IPv4 Subnetting

  • No Broadcast Addresses: IPv6 uses multicast for one-to-many communication instead of broadcast.
  • No Network/Broadcast Reserved Addresses: Unlike IPv4, the first and last addresses in an IPv6 subnet are typically usable host addresses. There's no concept of reserving addresses for network ID or broadcast.
  • Simplified Addressing: The fixed /64 boundary for host interfaces simplifies network design and enables SLAAC.
  • Header Simplicity: The IPv6 header is simpler than IPv4's, which can improve routing efficiency.

Other CIDR References

IPv4 CIDR

/0/1/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32