Table of Contents
Advertisement
Introduction
7.7 Bi-Directional Forward Detection (BFD)
7.7.1 Introduction
The BFD feature used to detect Ethernet link failures
physical link failure has been reported. There are situations, described below, in which packets are not being exchanged
802.3 MACs but the normal physical layer fault detection (such as LOL or LOF) does not report
between two
the failure. Once the failure has been reported by BFD, it is treated as a physical link failure and topology fea-
tures (such as RSTP) are activated to restore network connectivity. Following are some examples where this
could occur
7.7.2 BFD Protocol
The protocol is set up such that included in the transmitted packet is the value of how often the peer should
receive the packets. This CLI parameter is INTERVAL (1 to 65535 seconds), set on the transmit interface for
each end. There is also a discriminator value that is copied from incoming to outgoing packets.
Since each system can set a different transmit INTERVAL, there can be different values of when each system
should transmit to the other; in these cases, the higher value is used.
There is also a detect multiplier value (DETECTMULTIPLIER) that each system sends to each other. This is the
number of consecutive missed packets required to declare a failure.
The two values work together; the local peer will detect a failure if it has not received a packet in the (greater)
INTERVAL times the DETECTMULITPLER received from the remote system.
With this parameter configuration, in which the INTERVAL is the same (greater) value for each system, but the
DETECTMULITPLER does not need to be the same, the detection thresholds on the remote and local system
can be different.
If BFD has been enabled on one interface but disabled on the peer interface, the system that has BFD enabled
will declare a remote failure. However, it is possible to enable/disable the feature without interrupting existing
service.
When there is failure reported by BFD, the system responds in the same way as if there had been a physical fail-
ure, with the appropriate traps/logs, and any network topology feature (such as RSTP) is invoked to restore
Ethernet connectivity.
Finally, if there are both BFD and failing alarms on the interface, the failing alarms will mask the BFD alarms; the
user would not, for example, see both a BFD and failing alarm at the same time.
7.7.3 BFD Alarms
Following are the alarms for the different conditions that can be detected by the protocol.
For mis-wiring (i.e. receiving BFD packets with incorrect "discriminator" as described above). The alarm is
•
as follows:
Software Reference for SwitchBlade x3100 Series Switches (Network Management)
(packets not being properly forwarded or received) when no
Introduction
7-119
Advertisement
Chapters
Table of Contents
Troubleshooting
