ZyXEL Communications MES-2110 - Manual (Page 89)

MES-2110 User’s Guide
89
C
H A P T E R
11
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
SPEED RECOMMENDED
VALUE RECOMMENDED
RANGE ALLOWED
RANGE
Path
Cost 4Mbps 250 100 to 1000 1 to 65535
Path
Cost 10Mbps 100 50 to 600 1 to 65535