Which consideration must be made when using BFD in a network design?

Bidirectional Forwarding Detection (BFD) is a low-overhead, short-duration protocol intended to detect faults in the path between two forwarding engines. For the Cisco implementation of BFD to function correctly, two key prerequisites must be met on all participating routers. First, IP routing must be enabled to allow the routers to establish connectivity and exchange BFD control packets. Second, Cisco Express Forwarding (CEF) must be enabled. CEF is a high-performance forwarding mechanism, and BFD is tightly integrated with it to achieve fast detection times without impacting the main route processor. These are fundamental requirements for deploying BFD in a Cisco environment.

A. BFD does not require a First Hop Redundancy Protocol (FHRP). While BFD can enhance FHRPs like HSRP or VRRP, its primary use is with routing protocols and static routes.

B. While BFD can be used with static routes (which are not dynamic routing protocols), the underlying feature of "IP routing" must be enabled on the device for BFD to function.

C. Non-Stop Forwarding (NSF) and graceful restart are high-availability features that are complementary to BFD but are not prerequisites for its operation.

1. Cisco Systems

"IP Routing: BFD Configuration Guide

Cisco IOS XE Gibraltar 16.12.x". In the "Information About Bidirectional Forwarding Detection" section

under "Prerequisites for Bidirectional Forwarding Detection

" the guide explicitly states:

"Cisco Express Forwarding (CEF) must be enabled on all participating routers. (CEF is enabled by default on most Cisco platforms.)"

"IP routing must be enabled on all participating routers."

2. Cisco Systems

"Bidirectional Forwarding Detection

" IP Routing Configuration Guide

Cisco IOS Release 15M&T. In the "BFD Prerequisites" section

the document lists as a requirement:

"You must enable Cisco Express Forwarding on the router."

3. Cisco Systems

"Configuring BFD

" BGP Configuration Guide

Cisco IOS XR Release 7.3.x. In the "Prerequisites" section

it is noted:

"You must be in a user group associated with a task group that includes the proper task IDs... If you need assistance

contact your system administrator." While this is for XR

it reinforces that BFD has strict platform-level prerequisites

which for IOS/IOS-XE include CEF and IP routing.