ZyXEL Communications MES-2110 manual Bridge, STP Terminology, STP Path Costs

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Bridge

11.1 Overview

The MES-2110 supports Rapid Spanning Tree Protocol (RSTP) as defined in the IEEE 802.1w Rapid Spanning Tree Protocol standard.

(R)STP detects and breaks network loops and provides backup links between switches, bridges or routers. It allows a switch to interact with other (R)STP - compliant switches in your network to ensure that only one path exists between any two stations on the network.

The MES-2110 uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allows faster convergence of the spanning tree than STP (while also being backwards compatible with STP-only aware bridges). In RSTP, topology change information is directly propagated throughout the network from the device that generates the topology change. In STP, a longer delay is required as the device that causes a topology change first notifies the root bridge that then notifies the network. Both RSTP and STP flush unwanted learned addresses from the filtering database. In RSTP, the port states are Discarding, Learning, and Forwarding.

Note: In this user’s guide, “STP” refers to both STP and RSTP.

11.1.1 STP Terminology

The root bridge is the base of the spanning tree.

Path cost is the cost of transmitting a frame onto a LAN through that port. The recommended cost is assigned according to the speed of the link to which a port is attached. The slower the media, the higher the cost.

Table 23 STP Path Costs

	LINK	RECOMMENDED	RECOMMENDED	ALLOWED
	SPEED	VALUE	RANGE	RANGE
Path	4Mbps	250	100 to 1000	1 to 65535
Cost
Path	10Mbps	100	50 to 600	1 to 65535
Cost

MES-2110 User’s Guide

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