Persistent IP and Classful Networking

With an understanding of networks and network topology, we can look towards building larger camera networks and applications. In this article, we'll explain classful networks, persistent IP and how those work together.

As camera systems grow larger, understanding how IP addressing works becomes increasingly important. This article explains how Persistent IP behaves on JAI cameras that use classful networking assumptions, and how this differs from modern IP networking.

Some JAI camera series validate Persistent IP settings using classful networking rules. Although classful networking has been obsolete for many years, understanding its behaviour explains why certain Persistent IP configurations are accepted while others fall back to a Link-Local Address (LLA).

Newer JAI camera series are moving towards Classless Inter-Domain Routing (CIDR), the networking model used by modern operating systems and networking equipment.

Classful Networking

Historically, IPv4 addresses were divided into address classes, each with an associated default subnet mask.

The notation /24, /16, and /8 is called CIDR notation and indicates how many bits of the IP address belong to the network portion. For example:

• /24 = 255.255.255.0
• /16 = 255.255.0.0
• /8 = 255.0.0.0

Although this notation originated with CIDR, it is commonly used today to describe subnet masks.

Under the classful model:

• An address such as 192.168.1.13 is considered a Class C address and is expected to use the subnet mask 255.255.255.0 (/24).
• An address such as 132.16.11.13 is considered a Class B address and is expected to use the subnet mask 255.255.0.0 (/16).

For example:

Camera Behavior

When an unsupported subnet mask is assigned to the camera, the camera continues operating normally until it is rebooted.

During startup, the camera validates the Persistent IP configuration. If the configured subnet mask does not match the expected classful subnet for the configured IP address, the Persistent IP configuration is rejected.

The camera then attempts to obtain an address using DHCP. If no DHCP server is available, it falls back to a Link-Local Address (LLA) in the 169.254.x.x range.

Modern Networking (CIDR)

Modern IP networking uses Classless Inter-Domain Routing (CIDR), introduced in the early 1990s.

Unlike classful networking, CIDR allows the subnet mask to be chosen independently of the IP address. As a result, all of the following are valid configurations:

• 192.168.99.213/24
• 192.168.99.213/21
• 192.168.99.213/20
• 10.10.8.213/21
• 172.16.8.213/21

Modern operating systems, routers, and switches determine whether devices are on the same network using only the configured subnet mask. The IP address itself no longer determines the expected subnet size.

Future Direction

CIDR has replaced classful networking and is the standard used by modern networking equipment.

JAI is transitioning camera firmware to use CIDR-based validation of Persistent IP settings. This allows subnet masks such as /21 to be used consistently across all private IPv4 address ranges, including 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

To learn if your camera supports CIDR, contact our support or leave a comment!