Sub second switchcard failover is a redundancy mode available on systems with two switchcards. One switchcard is the

Failover 4.26.2F Switchcard

EOS 4.15.0F added support for a CLI knob to determine whether the L3 forwarding agent (responsible for programming FECs and routes into hardware) would react to BFD status events for an interface to update next-hop programming for FECs programmed in hardware. This required two events, one for the BFD session to transition to an “Up” status and a subsequent transition to a “Down” status. This is identical to how various protocols in EOS (i.e. BGP, IS-IS) leverage BFD for faster down detection, and is useful to allow the L3 forwarding agent to preemptively remove next hops that would later be deprogrammed due to protocol session status state.

TOI BFD Failover EOS 4.33.1F FRR

In certain VXLAN deployments with either NSX/Logical Router or EVPN IRB, active nodes hosting a virtual IP address

4.21.3F Virtual IP Failover