OS10 Enterprise Edition User Guide Release 10.4.1.0

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Bidirectional Forwarding Detection

The Bidirectional Forwarding Detection (BFD) protocol rapidly detects communication failures between two adjacent routers. BFD is a simple and lightweight replacement for link-state detection mechanisms in existing routing protocols. It also provides a failure detection solution for links with no routing protocol.

BFD provides forwarding-path failure detection that is performed in milliseconds, instead of seconds, as with routing protocol hello packets. Because BFD is independent of routing protocols, it provides consistent failure detection in a network. BFD eliminates multiple protocol-dependent timers and methods. Networks converge faster because BFD triggers link-state changes in the routing protocol sooner and more consistently.

BFD operates as a simple hello mechanism. Two neighboring routers running BFD establish a session using a three-way handshake. After the session is established, the routers exchange periodic control packets at sub-second intervals. If a router does not receive a hello packet within a specified time, routing protocols are notified that the forwarding path is down.

In addition, BFD sends a control packet when there is a state change or change in a session parameter. These control packets are sent without regard to transmit and receive intervals in a routing protocol.

BFD is an independent and generic protocol, which all media, topologies, and routing protocols can support using any encapsulation. OS10 implements BFD at Layer 3 (L3) and with User Datagram Protocol (UDP) encapsulation. BFD is supported for static and dynamic routing protocols, such as VRRP, OSPF, OSPFv3, IS-IS, and BGP.

  • NOTE: In this release, BFD is only supported for BGP.

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