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- Completeness: Even though each controller only has direct visibility and influence over a subset of the network, they should all work together to ensure each controller’s network topology view reflects the state of the entire network.
- Accuracy: Switches, ports and links go up and down. Each controller’s network view should always expose the correct state for various network elements. This also means that each controller’s network view should quickly change to reflect any changes in the underlying network.
- Low latency access: Network topology view is a heavily consumed piece of state and therefore it is very important that the chosen mechanism provide low latency access to the network view.
Approach
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In a given mastership term, the elected mater master receives various topology events from the device. These could be events such as switch connected, port online, port offline, link down, etc. The current master maintains a per-switch counter to tag the various topology events it has received from the device during its term. So the sequence number is a monotonically increasing counter that is initialized to 0 at the start of the term and is incremented when a new topology event is detected by the master.
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