VSI State Machine Handling Unexpected VDP Packets
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Solution Overview
Problem
Ethernet bridges implementing virtual Ethernet port aggregation (VEPA) mode often send unexpected Virtual Station Interface (VSI) discovery and configuration protocol (VDP) packets, causing VSI state machines to crash or enter indeterminate states due to misinterpretation of keep-alive messages as new sessions.
Innovation Solution
A network equipment test device emulates an edge relay and multiple VSIs to transmit keep-alive messages, receive and intercept unexpected de-associate messages, and log them, thereby preventing the VSI from entering an indeterminate state by modifying the VDP state machine to handle unexpected messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bridge transmits de-associate messages for all sessions, then session cleanup is initiated, but unexpected packets are sent to VSIs causing state machine crashes or indeterminate states
Solution Approach 1:
The test device performs preliminary actions by emulating the VSI state machine behavior before receiving unexpected packets. It pre-configures the expected message sequence and prepares the state machine to anticipate valid messages, allowing it to identify and reject unexpected packets before they can cause crashes or indeterminate states.
Solution Approach 2:
The test device acts as an intermediary between the bridge and the VSI state machine. It intercepts unexpected packets from the bridge and logs them, preventing these harmful packets from reaching the actual VSI state machine while still allowing the bridge to transmit its de-associate messages for session cleanup.
2Productivity
If the bridge delays transmission of de-associate messages due to buffering mechanisms, then resource constraints are managed, but keep-alive messages are misinterpreted as new session messages
Solution Approach 1:
The test device implements feedback by monitoring the bridge's message transmission timing and content. It detects when the bridge sends messages during the delayed transmission period and provides feedback about the actual message content, allowing the system to distinguish between keep-alive messages and new session messages based on their timing and characteristics.
Solution Approach 2:
The test device creates a copy of the VSI state machine behavior for simulation purposes. This copy processes messages in advance and records the expected behavior, allowing the system to compare actual bridge transmissions against the copied expected behavior to identify misinterpretations without affecting the actual VSI state machine.
3Stability of the object's composition
If the VSI enters retry queue to wait for session reestablishment, then session management is maintained, but unexpected messages cause the VSI to enter indeterminate state
Solution Approach 1:
The test device performs preliminary analysis of the VSI state machine's expected behavior during the retry queue period. It pre-determines which messages are valid during this state and which are not, creating a filter that prevents unexpected messages from causing indeterminate states while allowing the VSI to maintain session management stability.
Solution Approach 2:
The test device serves as an intermediary layer between the bridge and the VSI state machine during the retry period. It intercepts and filters messages, allowing only expected messages to reach the VSI while blocking unexpected messages that would cause indeterminate states, thus protecting the VSI's reliability without interfering with session management.
Data Source
AI summary
Methods, systems, and computer readable media for handling unexpected virtual station interface (VSI) discovery and configuration protocol (VDP) packets received by a VSI are disclosed. One method includes, at a network equipment test device, emulating an ER and VSIs behind the ER. The method further includes transmitting a keep-alive message for a session from one of the VSIs to a virtual Ethernet port aggregation (VEPA) bridge under test. The method further includes receiving a de-associate message from the bridge, tearing down the session, and attempting to re-establish the session with the bridge. The method further includes, while waiting to initiate the attempt to re-establish the session with the bridge, receiving an unexpected message from the bridge and intercepting and logging receipt of the at least one unexpected message.