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5-2
Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x
OL-23435-03
Chapter 5 Configuring Bidirectional Forwarding Detection
Information About BFD
• High Availability, page 5-4
• Virtualization Support, page 5-4
Asynchronous Mode
Cisco NX-OS supports the BFD asynchronous mode, which sends BFD control packets between two
adjacent devices to activate and maintain BFD neighbor sessions between the devices. You configure
BFD on both devices (or BFD neighbors). Once BFD has been enabled on the interfaces and on the
appropriate protocols, Cisco NX-OS creates a BFD session, negotiates BFD session parameters, and
begins to send BFD control packets to each BFD neighbor at the negotiated interval. The BFD session
parameters include the following:
• Desired minimum transmit interval—The interval at which this device wants to send BFD hello
messages.
• Required minimum receive interval—The minimum interval at which this device can accept BFD
hello messages from another BFD device.
• Detect multiplier—The number of missing BFD hello messages from another BFD device before
this local device detects a fault in the forwarding path.
Figure 5-1 shows how a BFD session is established. The figure shows a simple network with two routers
running OSPF and BFD. When OSPF discovers a neighbor (1), it sends a request to the local BFD
process to initiate a BFD neighbor session with the OSPF neighbor router (2). The BFD neighbor session
with the OSPF neighbor router is now established (3).
Figure 5-1 Establishing a BFD Neighbor Relationship
BFD Detection of Failures
Once a BFD session has been established and timer negotiations are complete, BFD neighbors send BFD
control packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more
accelerated rate. BFD detects a failure, but the protocol must take action to bypass a failed peer.
BFD sends a failure detection notice to the BFD-enabled protocols when it detects a failure in the
forwarding path. The local device can then initiate the protocol recalculation process and reduce the
overall network convergence time.
172.16.10.2 172.16.10.1
172.17.0.1172.18.0.1
BFD
BFD neighbors
3
OSPF
2
BFD
OSPF
2
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OSPF neighbors
1
Router A
Router B
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