Users Guide

Bidirectional Forwarding Detection 1433
Demand mode is advantageous in cases when the overhead of a periodic
protocol appears burdensome on a device, e.g., a router with a large number
of BFD sessions running.
Dell EMC Networking BFD does not support demand mode.
Echo Function
Echo mode is an auxiliary operation that may be used with either BFD mode.
When the echo function is active, a stream of BFD echo packets is
transmitted in such a way that the other system loops them back through its
forwarding path. If a configured number of consecutive packets of the echoed
data stream are not received, the session is declared to be down. Since the
echo function is handling the task of neighbor detection, the rate of periodic
transmission of BFD control packets may be reduced (in the case of
asynchronous mode) or eliminated completely (in the case of demand mode).
The echo function has the advantage of testing the forwarding path on the
remote system. This may reduce round-trip jitter and, thus, allow more
aggressive detection times, and can potentially catch some classes of failure
that might not otherwise be detected.
Limitations
• Dell EMC Networking BFD does not support demand mode.
• Dell EMC Networking BFD does not support authentication.
• The BFD feature provides notification to BGP or OSPF when an interface
is detected to not be in a forwarding state. No other protocols are
supported for notification.
• BFD is supported in the default VRF only.
• BFD should be configured on routed interfaces only. BFD should not be
configured mirrored ports or on interfaces enabled for IEEE 802.1x.
• BFD is supported across link aggregation groups, but does not detect
individual LAG member link failure.
• BFD does not operate on the out-of-band interface.