Bidirectional Forwarding Detection (BFD) | 1237Bidirectional Forwarding Detection (BFD)Bidirectional Forwarding Detection (BFD) is supported only on platforms: e czProtocol OverviewBidirectional Forwarding Detection (BFD) is a protocol that is used to rapidly detect communicationfailures between two adjacent systems. It is a simple and lightweight replacement for existing routingprotocol link state detection mechanisms. It also provides a failure detection solution for links on which norouting protocol is used.BFD is a simple hello mechanism. Two neighboring systems running BFD establish a session using athree-way handshake. After the session has been established, the systems exchange periodic controlpackets at sub-second intervals. If a system does not receive a hello packet within a specified amount oftime, routing protocols are notified that the forwarding path is down.BFD provides forwarding path failure detection times on the order of milliseconds rather than seconds aswith conventional routing protocol hellos. It is independent of routing protocols, and as such provides aconsistent method of failure detection when used across a network. Networks converge faster because BFDtriggers link state changes in the routing protocol sooner and more consistently, because BFD caneliminate the use of multiple protocol-dependent timers and methods.BFD also carries less overhead than routing protocol hello mechanisms. Control packets can beencapsulated in any form that is convenient, and, on Dell Force10 routers, sessions are maintained by BFDAgents that reside on the line card, which frees resources on the RPM. Only session state changes arereported to the BFD Manager (on the RPM), which in turn notifies the routing protocols that are registeredwith it.BFD is an independent and generic protocol, which all media, topologies, and routing protocols cansupport using any encapsulation. Dell Force10 has implemented BFD at Layer 3 and with UDPencapsulation. BFD functionality will be implemented in phases. The C-Series and E-Series support BFDon OSPF, IS-IS, VLANs, VRRP, LAGs, and physical ports based on the IETF internet draft documentdraft-ietf-bfd-base-03. On the S4810 and Z9000, BFD is supported on dynamic routing protocols such asBGP, IS-IS, and OSPF.
