Guidelines And Limitations - Cisco 7206 - VXR Router Configuration Manual

Chapter 5 Configuring Bidirectional Forwarding Detection
S e n d d o c u m e n t c o m m e n t s t o n e x u s 7 k - d o c f e e d b a c k @ c i s c o . c o m

Guidelines and Limitations

BFD has the following configuration guidelines and limitations:
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BFD supports BFD version 1.
BFD supports IPv4.
BFD supports single-hop BFD.
BFD for BGP supports single-hop EBGP and iBGP peers.
BFD supports keyed SHA-1 authentication beginning with Cisco NX-OS Release 5.2.
BFD supports the following Layer 3 interfaces—physical interfaces, port channels, subinterfaces,
and VLAN interfaces.
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.
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For Layer 2 port channels used by SVI sessions, you must enable LACP on the port channel.
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SVI limitations:
An ASIC reset will cause traffic disruption for other ports. This event could possibly cause SVI
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sessions on other ports to flap. Some triggers for an ASIC reset are port moves between VDCs,
reloading a VDC, or if the carrier interface is a virtual port channel (vPC), 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
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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.
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.
BFD over VLAN interfaces that have member ports only on a N7K-F132XL-15 module are not
supported. You should disable BFD over any VLAN with member ports only on a N7K-F132XL-15
module.
If you enable BFD at the router level (for example, from OSPF), any BFD sessions over a
N7K-F132XL-15 linecard will not come-up. See the Cisco Nexus 7000 Series NX-OS Unicast
Routing Configuration Guide, Release 5.x for information about OSPF and other routing
protocols.
When you configure the BFD Echo function on the distributed Layer 3 port channels, reloading a
member module flaps the BFD session hosted on that module, which results in a packet loss.
If you connect the BFD peers directly without a Layer 2 switch in between, you can use the BFD
per-link mode as an alternative solution.
Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x
Guidelines and Limitations
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