ZyXEL NWA-3163 User Guide - Page 144
Spanning Tree Protocol STP
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Chapter 8 Wireless Screen 8.3.1 Spanning Tree Protocol (STP) Spanning Tree Protocol (STP) detects and breaks network loops and provides backup links between switches, bridges or routers. It allows a bridge to interact with other STP-compliant bridges in your network to ensure that only one route exists between any two stations on the network. 8.3.1.1 Rapid STP The NWA uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allow faster convergence of the spanning tree (while also being backwards compatible with STP-only aware bridges). Using RSTP topology change information does not have to propagate to the root bridge and unwanted learned addresses are flushed from the filtering database. In RSTP, the port states are Discarding, Learning, and Forwarding. 8.3.1.2 STP Terminology The root bridge is the base of the spanning tree; it is the bridge with the lowest identifier value (MAC address). Path cost is the cost of transmitting a frame onto a LAN through that port. It is assigned according to the speed of the link to which a port is attached. The slower the media, the higher the cost - see the following table. Table 27 STP Path Costs LINK SPEED Path Cost Path Cost Path Cost Path Cost Path Cost Path Cost 4Mbps 10Mbps 16Mbps 100Mbps 1Gbps 10Gbps RECOMMENDE RECOMMENDE ALLOWED D VALUE D RANGE RANGE 250 100 to 1000 1 to 65535 100 50 to 600 1 to 65535 62 40 to 400 1 to 65535 19 10 to 60 1 to 65535 4 3 to 10 1 to 65535 2 1 to 5 1 to 65535 On each bridge, the root port is the port through which this bridge communicates with the root. It is the port on this switch with the lowest path cost to the root (the root path cost). If there is no root port, then this bridge has been accepted as the root bridge of the spanning tree network. For each LAN segment, a designated bridge is selected. This bridge has the lowest cost to the root among the bridges connected to the LAN. 144 NWA-3160 Series User's Guide