Allied Telesis AT-S24 - Manual (Page 45)

AT-S24 Version 2.01 User’s Guide
45
Configuring the Spanning Tree Protocol
The Spanning Tree Protocol (STP) prevents data loops when end stations
in extended networks send and receive packets through multiple or
redundant paths.
Each switch is a learning bridge with the following functions:
❑ Learns source MAC addresses of incoming packets by storing the
information in a forwarding table (see also Chapter 4,
Configuring the MAC Address Table).
❑ Forwards the packet to the port or ports specified in the MAC
forwarding table. The switch does not resend the packet out the
port on which it was initially received.
❑ Automatically ages out the addresses (deletes the information
from the forwarding table) if a MAC address is undetected by any
port within a user-defined or a default elapsed time (300 seconds).
❑ Updates the MAC address table automatically as you add, remove,
or relocate devices on the network.
❑ Determines the best single route to a destination device when
you enable STP via automatic selection of a root bridge and root
ports.
❑ Updates other bridges with topology information by periodically
sending Bridge Protocol Data Units (BPDUs).
The root port is chosen by a bridge as that bridge’s preferred path to the
root bridge. Only one bridge is elected as the root bridge.
Once the STP parameters have been configured, bridges can make a
determination on the best single path to a destination within a given
VLAN. A formula determines the amount of time it takes for the topology
to reconfigure, depending upon the spanning tree values you use. Refer
to the IEEE specification for details.
Most users generally keep the default STP parameters to allow bridges to
reconfigure themselves automatically if the topology changes or if
bridges become disabled.
For a brief overview of STP, go to Appendix B, Spanning Tree
Concepts.