BFD Over Member Links on Link Bundles
BFD supports BFD sessions on individual physical bundle member links to monitor Layer 3 connectivity on
those links, rather than just at a single bundle member as in prior releases (Figure 37).
Figure 10: BFD Sessions in Original BFD Over Bundles and Enhanced BFD Over Bundle Member Links Architectures
When you run BFD on link bundles, you can run an independent BFD session on each underlying physical
interface that is part of that bundle.
When BFD is running on a link bundle member, these layers of connectivity are effectively tested as part of
the interface state monitoring for BFD:
• Layer 1 physical state
• Layer 2 Link Access Control Protocol (LACP) state
• Layer 3 BFD state
The BFD agent on each bundle member link monitors state changes on the link. BFD agents for sessions
running on bundle member links communicate with a bundle manager. The bundle manager determines the
state of member links and the overall availability of the bundle. The state of the member links contributes to
the overall state of the bundle based on the threshold of minimum active links or minimum active bandwidth
that is configured for that bundle.
Overview of BFD State Change Behavior on Member Links and Bundle Status
This section describes when bundle member link states are characterized as active or down, and their effect
on the overall bundle status:
• You can configure BFD on a bundle member interface that is already active or one that is inactive. For
the BFD session to be up using LACP on the interface, LACP must have reached the distributing state.
A BFD member link is “IIR Active” if the link is in LACP distributing state and the BFD session is up.
• A BFD member link is “IIR Attached” when the BFD session is down, unless a LACP state transition
is received.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
138
Implementing BFD
BFD Over Member Links on Link Bundles
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