ZyXEL Communications VES-1616 manual Filtering Database Instability

ZyXEL VES-1616/24FA-5x Series Support Notes

2. Filtering Database Instability:

When multiple copies of a frame arrive at different ports of a switch, the MAC entry instability in Filtering Database will occur.

zHost sends a unicast frame to a router (source MAC address is host's MAC, destination MAC address is Router's MAC). Both Switch A and Switch B will receive this frame and learn the MAC address of the host on Port 2.

zSwitch A has not yet learned the MAC address of Router. So Switch A will flood a copy of the received frame to Segment B.

zWhen the copy of the frame from Switch A arrives at Switch B, Switch B will remove the first entry (Host MAC address on Port 2) in Filtering Database and add a new mapping of Host MAC address on Port 1. Switch B incorrectly learn Host MAC address on Port 1.

zSwitch B can't forward the frames properly because the instability of mapping MAC address to Port.

How STP Works

Spanning Tree provides a loop-free network. When a switch supporting STP recognizes a loop in the network topology, it blocks one or more redundant ports.

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