Spanning Tree - ZyXEL Communications MGS3600-24F User Manual

F M
RONT ATTER

7.5 Spanning Tree

Use the Spanning Tree sub-menu to configure STP, RSTP and MSTP.
The Spanning Tree Protocol (STP) 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 STP-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.
STP uses a distributed algorithm to select a bridging device (STP-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. Then 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. All ports connected to designated bridging devices are assigned as designated ports. After determining
the lowest cost spanning tree, STP enables all root ports and designated ports, and disables all other ports. Network packets are therefore only for-
warded between root ports and designated ports, eliminating any possible network loops.
Once a stable network topology has been established, all bridges listen for Hello BPDUs (Bridge Protocol Data Units) transmitted from the Root
Bridge. If a bridge does not get a Hello BPDU after a predefined interval (Maximum Age), the bridge assumes that the link to the Root Bridge is
down. This bridge will then initiate negotiations with other bridges to reconfigure the network to reestablish a valid network topology.
MGS3600-24F/XGS3600-26F/XGS3600-28F 7-29 U ' G
SER S UIDE