An IPv4 public /30 static subnet is a block of IPv4 addresses that includes four individual IP addresses. It is often used in networking scenarios that require a small number of publicly routable IP addresses.

Here’s an explanation of the key components of an IPv4 /30 subnet:

  1. IPv4 Address Format: IPv4 addresses are typically written in decimal format, consisting of four sets of numbers separated by periods (e.g., 192.168.1.1). Each set can range from 0 to 255, making a total of 2^32 (approximately 4.3 billion) unique IPv4 addresses.
  2. Subnet Mask: A subnet mask is used to divide an IPv4 address into network and host portions. It consists of 32 bits, with a series of contiguous “1s” followed by “0s.” In CIDR notation, a subnet mask is represented as “/x,” where “x” is the number of bits set to “1.” For example, a /30 subnet mask has 30 bits set to “1” and 2 bits set to “0,” allowing for a total of four possible IP addresses.
  3. /30 Subnet: A /30 subnet has a subnet mask of 255.255.255.252 in decimal notation or /30 in CIDR notation. This means that the first 30 bits of the IPv4 address are used for network identification, and the remaining 2 bits are available for host addresses.
  4. Number of Usable IP Addresses: In a /30 subnet, there are two host addresses available for assignment because the first and last addresses in the subnet are reserved. The usable IP addresses are typically used for network equipment, such as routers or point-to-point links, where two IP addresses are needed—one for each end of the connection.
  5. Reserved Addresses: In a /30 subnet, the first address (lowest numerical value) is reserved as the network address, and the last address (highest numerical value) is reserved as the broadcast address. These addresses cannot be assigned to individual devices on the network.

Here’s a breakdown of the four IP addresses in a /30 subnet:

  • Network Address: The first IP address (e.g., 192.168.1.0) is the network address and represents the network itself.
  • Usable Host Address 1: The second IP address (e.g., 192.168.1.1) can be assigned to one end of a point-to-point link or a network device.
  • Usable Host Address 2: The third IP address (e.g., 192.168.1.2) can be assigned to the other end of the same point-to-point link or another network device.
  • Broadcast Address: The fourth IP address (e.g., 192.168.1.3) is the broadcast address and is used to send a broadcast message to all devices within the subnet. It is not assigned to a specific device.

/30 subnets are commonly used in scenarios where conserving IP addresses is important, such as in small-scale point-to-point connections or for secure isolated network segments. They provide just enough addresses for the required connections while minimizing IP address consumption.