Explains the impacts of port hopping on control plane connections and BFD sessions when controller devices experience failures and recovery.
Port hopping effects are network behaviors that
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cause control connections and BFD sessions to shut down and restart when controller devices recover from failures
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occur when devices attempt to re-establish connections by switching to different ports, and
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impact the stability of the overlay network control plane during recovery scenarios.
Port hopping behavior details
Cisco vEdge devices use port hopping to make every attempt to keep the control plane of the overlay network up and operational. If a controller device—Cisco SD-WAN Validator, Cisco SD-WAN Manager, or Cisco SD-WAN Controller—goes down for any reason and the Cisco vEdge devices remain up, when the controller device comes back up, the connection between it and the Cisco vEdge device might shut down and restart, and in some cases the BFD sessions on the Cisco vEdge device might shut down and restart. This behavior occurs because of port hopping: When one device loses its control connection to another device, it port hops to another port in an attempt to re-establish the connection.
Changing the Cisco SD-WAN Controller graceful-restart timers result in an OMP peer flap, independent of whether or not port-hop is enabled. We recommend that you change Cisco SD-WAN Controller graceful-restart timers with redundant Cisco SD-WAN Controller peering (where only a single Cisco SD-WAN Controller configuration is changed at a time) or during a maintenance period when a data plane disruption can be tolerated.
Port hopping scenarios
Two examples illustrate when this might occur:
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When Cisco SD-WAN Validator crashes, Cisco SD-WAN Manager might take down all connections to the Cisco vEdge devices. The sequence of events that occurs is as follows: When Cisco SD-WAN Validator crashes, Cisco SD-WAN Manager might lose or close all its control connections. Cisco SD-WAN Manager then port hops, to try to establish connections to the Cisco SD-WAN Controllers on a different port. This port hopping on Cisco SD-WAN Manager shuts down and then restarts all its control connections, including those to the Cisco vEdge devices.
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All control sessions on all Cisco SD-WAN Controllers go down, and BFD sessions on the Cisco vEdge devices remain up. When any one of the Cisco SD-WAN Controllers comes back up, the BFD sessions on the routers go down and then come back up because the Cisco vEdge devices have already port hopped to a different port in an attempt to reconnect to Cisco SD-WAN Controllers.