ZyXEL Communications ES3500 Series Spanning Tree Protocol, 13.1 STP/RSTP Overview, Table, VALUE, RANGE, RANGE, ALLOWED, LINK SPEED, RECOMMENDED, RECOMMENDED, STP Path Costs

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Spanning Tree Protocol

The Switch supports Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP) as defined in the following standards.

•IEEE 802.1D Spanning Tree Protocol•IEEE 802.1w Rapid Spanning Tree Protocol•IEEE 802.1s Multiple Spanning Tree Protocol

The Switch also allows you to set up multiple STP configurations (or trees). Ports can then be assigned to the trees.

13.1 STP/RSTP Overview

(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 Switch 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 and then the root bridge 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.

13.1.1 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 31	STP Path Costs
		LINK SPEED	RECOMMENDED	RECOMMENDED	ALLOWED
			VALUE	RANGE	RANGE
Path Cost		4Mbps	250	100 to 1000	1 to 65535
Path Cost		10Mbps	100	50 to 600	1 to 65535
Path Cost		16Mbps	62	40 to 400	1 to 65535
Path Cost		100Mbps	19	10 to 60	1 to 65535

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ES3500 Series User’s Guide