SMC Networks SMC8624/48T manual Spanning Tree Algorithm Configuration, 116

CONFIGURING THE SWITCH

Spanning Tree Algorithm Configuration

The Spanning Tree Algorithm (STA) can be used to detect and disable network loops, and to provide backup links between switches, bridges or routers. This allows the switch to interact with other bridging devices (that is, an STA-compliant switch, bridge or router) in your network to ensure that only one route exists between any two stations on the network, and provide backup links which automatically take over when a primary link goes down.

The spanning tree algorithms supported by this switch include these versions:

•STP – Spanning Tree Protocol (IEEE 802.1D)

•RSTP – Rapid Spanning Tree Protocol (IEEE 802.1w)

•MSTP – Multiple Spanning Tree Protocol (IEEE 802.1s)

STA uses a distributed algorithm to select a bridging device (STA-compliant switch, bridge or router) that serves as the root of the spanning tree network. It selects a root port on each bridging device (except for the root device) which incurs the lowest path cost when forwarding a packet from that device to the root device. It selects a designated bridging device from each LAN which incurs the lowest path cost when forwarding a packet from that LAN to the root device.

It then selects a port on the designated bridging device to communicate with each attached LAN or host device as a designated port. After determining the lowest cost spanning tree, it enables all root ports and designated ports, and disables all other ports. Network packets are therefore only forwarded between root ports and designated ports, eliminating any possible network loops.

3-116