Hitless VLAN Pruning Upgrade on Single Supervisor Network Devices
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Solution Overview
Problem
During a control plane outage in network devices, especially single supervisor devices, the inability to transmit periodic control plane messages leads to unsubscribing from VLANs, resulting in potential disruption of flood traffic to end devices, as existing protocols rely on timely message exchange for VLAN subscription management.
Innovation Solution
The network device transmits a control plane message before a software upgrade to prevent premature unsubscribing by reclassifying itself as incompatible with VLAN pruning, maintaining subscription until the control plane is available, using techniques like VTP or MVRP to ensure continuous flood traffic delivery by extending timers or changing neighbor states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network device transmits periodic control plane messages to maintain VLAN subscriptions, then the VLAN subscription is maintained, but during control plane outage the device cannot transmit these messages and loses subscription
Solution Approach 1:
The network device performs preliminary actions by sending a first control plane message to neighboring devices before the control plane outage occurs. This message pre-configures the neighboring devices to maintain the VLAN subscription state even when periodic messages stop during outage, effectively preparing the system in advance to handle the upcoming control plane unavailability.
Solution Approach 2:
The patent introduces an intermediary mechanism where a single supervisor network device acts as a mediator between the control plane and data plane. During control plane outage, this supervisor device maintains VLAN subscriptions by managing timer extensions and coordinating with neighboring devices, serving as an intermediary that keeps the data plane operational despite control plane unavailability.
2Use of energy by moving object
If the network device unsubscribes from VLANs during control plane outage to free resources, then resource usage is reduced, but flood traffic delivery to end devices is disrupted
Solution Approach 1:
The patent segments the network device functionality into separate supervisor and non-supervisor roles. The supervisor device maintains VLAN subscriptions and controls resource usage, while non-supervisor devices can have their subscriptions pruned. This segmentation allows resource optimization in non-critical paths while preserving flood traffic delivery through the supervisor device.
Solution Approach 2:
The patent changes the timer parameter that controls VLAN subscription maintenance. During control plane outage, the timer is extended or suspended, allowing the network device to maintain VLAN subscriptions longer than normal. This parameter change enables continuous flood traffic delivery despite the control plane being unavailable for periodic message transmission.
3Ease of manufacture
If the network device performs Software Upgrade (ISSU) with single supervisor, then maintenance is enabled, but control plane outage occurs during upgrade
Solution Approach 1:
The patent applies beforehand cushioning by pre-configuring timer extensions and subscription maintenance mechanisms before the Software Upgrade begins. This cushioning ensures that even when the control plane becomes unavailable during the upgrade process, the VLAN subscriptions remain active and flood traffic continues to flow, protecting against the anticipated control plane outage.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining VLAN subscriptions and flood traffic delivery throughout the Software Upgrade process. The supervisor device continues to manage subscriptions and extend timers during the upgrade, ensuring that the data plane functionality remains continuous even while the control plane is temporarily unavailable for the upgrade operations.
Data Source
AI summary
Upon receiving a first message, from the second network device, indicating that the second network device is incompatible with one or more virtual local area network (VLAN) pruning techniques, a timer on a first network device is configured to expire after a predetermined period of time. The first network device is configured to maintain a subscription for the second network device to one or more VLANs until the timer expires. The second network device is configured to transmit the first message in response to detecting an upcoming control plane outage at the second device. Prior to the timer expiring, embodiments transmit data assigned to the one or more VLANs to the second network device. Embodiments also periodically receive update messages, from the second network device, identifying one or more VLANs to which the second network device wants to subscribe.