Bundle Fast Convergence
The Bundle Fast Convergence (BFC) feature provides the ability to converge bundle members within sub
seconds instead of multiple seconds. This feature provides faster bundle member convergence with deterministic
traffic outage bounded within 50 milliseconds.
On bundle member shut, the packet drop is reduced to less than 50 milliseconds. On multiple members shut,
the loss is less than (n*50ms), where 'n' is the number of members being shut.
BFC Functionality
The BFC feature decouples the tasks FIB is performing for bundle membership updates. This splits the FIB's
bundle membership tasks into two separate threads:
• FAST Update (FRR thread): This option does In-Place-Modify (IPM) only, which guarantees deterministic
outage time. FIB gets the bundle member down directly from Bundle Interface Manager (BIM) using
Fast Protect Infra (similar to TE FRR update model).
• SLOW Update (Adjacency thread): Adjacency update from AIB, which is the current processing logic;
does the following tasks:
• IPM on the current hardware entries
• Create a new set of hardware entries with new membership information
BFC tracks the bundle members that are down from FAST channel by setting a pending flag, then when
SLOW update AIB is received it looks for FAST down member. If the BFC finds the FAST down member,
it clears the pending flag, if it does not, it processes the SLOW update and considers the FAST down member
as down and programs to the hardware.
Condition for BFC
The bundle must contain N members (they may be of different bandwidth, belong to different slices or Line
Cards) and at the most N-1 members could be shut down in a single or multiple commits.
Shutting down bundle member link/s in single or serial commits is the only valid trigger for BFC. Bundle fast
convergence time is calculated based on Frame delta and number of links affected. Convergence time <
Number of links affected * 50ms --> 0 (50ms). Convergence time must be < 50ms per flow in the traffic.
Note
Sample BFC Data
The following example shows convergence time data for sixteen individual flows that traffic was sent onto
on dual router topology.
This data is taken for a bundle which has ten members including one 100Gig and nine 10Gig members where
nine members (including 100Gig) are shut down with individual commits in order to trigger the BFC feature.
DirectionPacket Loss Duration (ms)Frame
Delta
Egress6.667337
Egress1.18761
Interface and Hardware Component Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
70
Configuring Link Bundling
Bundle Fast Convergence
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