Bidirectional Forwarding Detection Overview

BFD, or Bidirectional Forwarding Detection, is a fast failure detection protocol that enables RBFS devices to identify broken links quickly. This quick detection helps to ensure fast rerouting and minimizes downtime.

BFD swiftly identifies network failures between neighboring devices using a simple hello mechanism. BFD enabled RBFS devices establish a session and exchange BFD control packets at regular intervals. If a device stops receiving BFD packets from its neighbor within the predefined detection time, it assumes that the path has failed. This failure information is then communicated to routing protocols such as OSPF, BGP, or IS-IS, allowing these protocols to reroute traffic immediately.

Routing protocols, such as OSPF and BGP, rely on hello and dead timers that can range from 1 to 10 seconds to detect failures. BFD ensures rapid convergence by detecting failures almost instantly and signaling routing protocols to switch paths quickly.

Imagine where Router A is connected to Router B. The routing protocol, such as OSPF, indicates that the neighbor is operational. However, due to a hardware fault, packets cannot actually be transmitted from Router A’s interface to Router B. Without BFD, it could take several seconds for OSPF to recognize this problem. With BFD, the loss of BFD packets can signal a forwarding path failure swiftly.

This BFD implementation offers operational visibility and provides details such as session state (up/down/init), Timers (transmit interval, receive interval, detection time), Detection multiplier (how many missed packets before declaring down), packet statistics (sent/received counts) and last-down reason (for example, timeout, admin shutdown, remote fault).

Routing applications in RBFS can use BFD functionality through the OAMD infrastructure. OAM Daemon provides an interface that allows applications to create and delete BFD sessions.