Connection Tracking

Connection tracking is a method used by security systems to monitor and manage network connections. It keeps a record of active connections between devices in a network, allowing for intelligent decision-making about whether to permit or deny traffic based on the state of these connections. This approach helps maintain security and ensures that legitimate traffic can flow freely while unauthorized access is blocked.

When a device initiates communication, such as when you send a request to a server, connection tracking records the details of this interaction, including the IP addresses, protocol used, and port numbers involved. This information is stored as part of the connection state. For example, if you use a command from your home computer to communicate with an instance in the cloud, connection tracking will log this interaction. Any response from the instance will be recognized as part of the established connection and will be allowed to proceed, even if outbound security rules might otherwise block it.

Connection tracking is particularly important for protocols like TCP (Transmission Control Protocol), UDP (User Datagram Protocol), and ICMP (Internet Control Message Protocol). For these protocols, connection tracking manages both the initiation and response of network communications. For other protocols, it tracks only the IP address and protocol number. If a host sends a specific type of traffic to an instance and the instance responds within 600 seconds, the response is treated as part of the initial communication.

One key feature of connection tracking is its stateful security nature. This means it allows returning traffic to flow regardless of outbound rules, as long as it matches an initiated connection. However, not all traffic is tracked. If security group rules are broadly permissive (e.g., allowing all traffic from any source), the return traffic may not be tracked.

Connection tracking also has limits. Each instance can track a certain number of connections at any time. If this number is exceeded, new connections cannot be established, leading to potential communication failures. Systems can monitor this through network performance metrics, helping manage and optimize the number of tracked connections.

Ultimately, connection tracking enhances network security by ensuring that only legitimate, stateful traffic flows through, while unauthorized or potentially harmful traffic is blocked.