Specifications

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7-4
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 7 Configuring Bidirectional Forwarding Detection for BGP
Default Settings
• BFD depends on a Layer 3 adjacency information to discover topology changes, including Layer 2
topology changes. A BFD session on a VLAN interface (SVI) may not be up after the convergence
of the Layer 2 topology if there is no Layer 3 adjacency information available.
• Port channel configuration limitations:
– For Layer 3 port channels used by BFD, you must enable LACP on the port channel.
– For Layer 2 port channels used by SVI sessions, you must enable LACP on the port channel.
• SVI limitations:
– An ASIC reset will cause traffic disruption for other ports. This event could possibly cause SVI
sessions on other ports to flap. Some triggers for an ASIC reset are port moves between VDCs
or reloading a VDC. In these cases, BFD is not supported over the SVI interface.
– When you change the topology (for example, add or delete a link into a VLAN, delete a member
from a Layer 2 port channel, and so on), the SVI session could be affected. It may go down first
and then come up after the topology discovery is finished.
Tip If you do not want the SVI sessions to flap and you need to change the topology, you can disable
the BFD feature before making the changes and reenable BFD after the changes have been made.
You can also configure the BFD timer to be a large value (for example, 5 seconds), and change
it back to a fast timer after the above events complete.
• Cisco NX-OS does not distribute the BFD operation to compatible modules to offload the CPU for
BFD packet processing.
• BFD does not support stateless restarts and in-service software upgrades (ISSUs).
• If you want to enable BFD for a peer reachable through a port channel, you must configure LACP
on the port channel.
• BFD echo mode and Unicast Reverse Path Forwarding (URPF) are mutually exclusive and cannot
both be enabled on a BFD interface. If you want to configure an interface for BFD, you must disable
either BFD echo mode or URPF.
Default Settings
Table 7-1 lists the default settings for BFD parameters.
Table 7-1 Default BFD Parameters
Parameters Default
BFD feature Disabled
Required minimum receive interval 250 milliseconds
Desired minimum transmit interval 250 milliseconds
Detect multiplier 3
Echo function Enabled
Mode Asynchronous
Port channel Logical mode (one session per source-destination
pair address).