DELL S50V User Manual
Bidirectional Forwarding Detection | 169
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Bidirectional Forwarding Detection
c e
BFD is supported on E-Series ExaScale
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with FTOS 8.2.1.0 and later.
Protocol Overview
Bidirectional Forwarding Detection (BFD) is a protocol that is used to rapidly detect communication
failures between two adjacent systems. It is a simple and lightweight replacement for existing routing
protocol link state detection mechanisms. It also provides a failure detection solution for links on which no
routing protocol is used.
failures between two adjacent systems. It is a simple and lightweight replacement for existing routing
protocol link state detection mechanisms. It also provides a failure detection solution for links on which no
routing protocol is used.
BFD is a simple hello mechanism. Two neighboring systems running BFD establish a session using a
three-way handshake. After the session has been established, the systems exchange periodic control
packets at sub-second intervals. If a system does not receive a hello packet within a specified amount of
time, routing protocols are notified that the forwarding path is down.
three-way handshake. After the session has been established, the systems exchange periodic control
packets at sub-second intervals. If a system does not receive a hello packet within a specified amount of
time, 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 as
with conventional routing protocol hellos. It is independent of routing protocols, and as such provides a
consistent method of failure detection when used across a network. Networks converge faster because BFD
triggers link state changes in the routing protocol sooner and more consistently, because BFD can
eliminate the use of multiple protocol-dependent timers and methods.
with conventional routing protocol hellos. It is independent of routing protocols, and as such provides a
consistent method of failure detection when used across a network. Networks converge faster because BFD
triggers link state changes in the routing protocol sooner and more consistently, because BFD can
eliminate the use of multiple protocol-dependent timers and methods.
BFD also carries less overhead than routing protocol hello mechanisms. Control packets can be
encapsulated in any form that is convenient, and, on Dell Force10 routers, sessions are maintained by BFD
Agents that reside on the line card, which frees resources on the RPM. Only session state changes are
reported to the BFD Manager (on the RPM), which in turn notifies the routing protocols that are registered
with it.
encapsulated in any form that is convenient, and, on Dell Force10 routers, sessions are maintained by BFD
Agents that reside on the line card, which frees resources on the RPM. Only session state changes are
reported to the BFD Manager (on the RPM), which in turn notifies the routing protocols that are registered
with it.
BFD is an independent and generic protocol, which all media, topologies, and routing protocols can
support using any encapsulation. Dell Force10 has implemented BFD at Layer 3 and with UDP
encapsulation. BFD functionality will be implemented in phases. OSPF, IS-IS (not on C-Series), VRRP,
VLANs, LAGs, static routes, and physical ports support BFD, based on the IETF internet draft
draft-ietf-bfd-base-03.
support using any encapsulation. Dell Force10 has implemented BFD at Layer 3 and with UDP
encapsulation. BFD functionality will be implemented in phases. OSPF, IS-IS (not on C-Series), VRRP,
VLANs, LAGs, static routes, and physical ports support BFD, based on the IETF internet draft
draft-ietf-bfd-base-03.