16-3
Spanning Tree Protocol (STP)
Overview
Spanning Tree Protocol
(STP)
As recommended in the IEEE 802.1Q VLAN standard, the Switch 4108GL uses
single-instance STP. (As a result, the switch generates untagged Bridge
Protocol Data Units—BPDUs.) This implementation creates a single spanning
tree to make sure there are no network loops associated with any of the
connections to the switch, regardless of whether multiple VLANs are config-
ured on the switch. Thus, these switches do not distinguish between VLANs
when identifying redundant physical links. If VLANs are configured on th e
switch, see “STP Operation with 802.1Q VLANs” on page 16-12.
STP Fast Mode for Overcoming Server Access Failures. If an end node
is configured to automatically access a server, the duration of the STP startup
sequence can result in a “server access failure”. On ports where this is a
problem, configuring STP Fast Mode can eliminate the failure. For more
information, see “STP Fast Mode” on page 16-10. The next sections describe
how to configure STP on the switch. For more information on STP operation,
see “How STP Operates” on page 16-9.
In the factory default configuration, STP is off. If a redundant l ink (loop) exists
between nodes in your network, you should enable Spanning Tree.
Note STP retains its current parameter settings when disabled. Thus, if you
disable STP, then later re-enable it, the parameter settings will be the same
as before STP was disabled.
Caution Because the switch automatically gives faster links a higher priority, the
default STP parameter settings are usually adequate fo r spanning tree
operation. Also because incorrect STP settings c an adversely affect network
performance, you should not make changes unless you have a strong under-
standing of how STP operates. For more on STP, see the IEEE 802.1D standard.