Configuring Bfd Parameters - Dell PowerConnect B-RX Configuration Manual

BiDirectional Forwarding Detection (BFD)
The BigIron RX provides support for Bidirectional Forwarding Detection (BFD), which defines a
method of rapid detection of the failure of a forwarding path by checking that the next hop router is
alive. Without BFD enabled, it can take from 3 to 30 seconds to detect that a neighboring router is
not operational causing packet loss due to incorrect routing information at a level unacceptable for
real-time applications such as VOIP and video over IP. Using BFD, you can detect a forwarding path
failure in 300 milliseconds or less depending on your configuration.
A BFD session is automatically established when a neighbor is discovered for a protocol provided
that BFD is enabled on the interface on which the neighbor is discovered and BFD is also enabled
for the protocol (by interface or globally). Once a session is set-up, each router transmits control
messages at a high rate of speed that is negotiated by the routers during the session setup. To
provide a detection time of 150 milliseconds, it is necessary to process 20 messages per second of
about 70 to 100 bytes each per each session. A similar number of messages also needs to be
transmitted out per each session. Once a session is set-up, that same message is continuously
transmitted at the negotiated rate and a check is made that the expected control message is
received at the agreed frequency from the neighbor. If the agreed upon messages are not received
from the neighbor within a short period of time, the neighbor is considered to be down. The
maximum number of sessions supported on an interface module (LP) is 20 while the maximum per
system is 100.
NOTE
BFD session establishment on an interface does not start until 90 seconds after the interface
comes up. The reason for this delay is to ensure that the link is not effected by unstable link
conditions which could cause BFD to flap. This delay time is not user configurable.
The BFD Control Message is an UDP message with destination port 3784.
NOTE
BFD version 0 is not supported in this implementation and BFD version 1 is not compatible with BFD
version 0.
NOTE
BFD supports multi-slot trunks in cases where all BFD packet are transmitted only on a single path
which does not change unless the trunk active membership changes. BFD is not be supported on
multi-slot trunks where per-packet switching is used such that the path taken by the BFD packets
will vary per packet.

Configuring BFD parameters

When you configure BFD you must set timing and interval parameters. These are configured on
each interface. When two adjacent interfaces with BFD are configured, they negotiate the
conditions for determining if the connection between them is still active. The following command is
used to set the BFD parameters.
BigIron RX Series Configuration Guide
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