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Does BGP guarantee convergence?
All Interior Gateway Protocols rely on convergence to function properly. To have converged it is the normal state of an operational autonomous system. The Exterior Gateway Routing Protocol BGP typically never converges because the Internet is too big for changes to be communicated fast enough.
How long does it take for BGP to converge?
This takes up to 60 seconds depending on the when the BGP Scanner process last ran. So even with a super optimized IGP, BGP will be very slow to converge.
Why is BGP slow?
There are several causes of a peer being slow: There is packet loss or high traffic on the link to the peer, and the throughput of the BGP TCP connection is very low. The peer has a heavy CPU load and cannot service the TCP connection at the required frequency.
What is the expected convergence time for BGP?
With these values the expected fault detection time is about 60ms or 300ms respectively. These are the worst cases, as a possible failure of the physical interface is usually immediately reflected with teardown of the BGP session. However, the resulting fast converge time applies only to the devices involved in the link failure.
How does a backup leaf work in BGP?
Backup leaf immediately propagates the new best default route to BGP route-reflectors; BGP update then cascades to all the remaining leafs. As a result, two complete BGP update propagation and convergence processes are required to install the new routing path on all devices.
What should the packet rate be for BGP?
The packet rates are configurable but platform dependent, typical values are 10×3 (10 ms interval and 3 lost packets needed for session-down detection) or 100×3. I personally suggest 10×6 values for critical environments or a more relaxed 50×6 in other environments.
How is BGP used in the control plane?
BGP provides an “in-band” control-plane that checks the status of all links and devices in the forwarding path and selects the primary and backup paths. The total time required for a complete failover depends exclusively on BFD timers plus BGP state propagation delay.