MNS-BB
Software User Guide
-69-
13.0
Spanning Tree Protocol (STP)
13.1 STP
Features
The switch uses the IEEE 802.1D Spanning Tree Protocol (STP). When this STP is enabled, it
ensures that only one path at a time is active between any two nodes on the network. In networks
where more than one physical path exists between two nodes, STP ensures only a single path is active
by blocking all redundant paths. Enabling STP is necessary in such networks because having more
than one path between a pair of nodes causes loops in the network which can result in duplication of
messages. This duplication leads to a “broad-cast storm” that can bring down the network.
Note:
You should enable STP in any switch that is part of a redundant physical link (loop topology).
(It is recommended that you enable STP on all switches belonging to a loop topology.)
As recommended in the IEEE 802.1Q VLAN standard, the LE2425A and LEV2525A Switches use
single-instance STP
. This means a single spanning tree is created to make sure there are no network
loops associated with any of the connections to the switch. This works regardless of whether VLANs
are configured on the switch. Thus, these switches do not distinguish between VLANs when
identifying redundant physical links.
13.2
Feature Default
enable/disable STP disabled
reconfiguring general operation priority: 32768
max age: 20 s
hello time: 2 s
fwd. delay: 15 s
reconfiguring per-port STP path cost: var
priority: 128
mode: norm
monitoring STP n/a
In the factory default configuration, STP is off. If a redundant link (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 for spanning tree operation. Also because incorrect STP
settings can adversely affect network performance, you should not make changes unless you have a
strong understanding of how STP operates. For more on STP, see the IEEE 802.1D standard.
13.3
Viewing the Current STP Configuration.
Regardless of whether STP is disabled (the default), this command lists the switch’s full STP
configuration, including general settings and port settings.
Syntax: show stp <config | port | age>
LE2425A#
show stp config
STP Bridge Configuration:
In the default configuration, STP appears as shown here:
Spanning Tree Enabled(Global)
:NO
Spanning Tree Enabled(Ports)
:YES, 9,10,11,12,13,14,15,16,17,18,19,20,21,22
Bridge Priority
:32768
Bridge Forward Delay
:15
Bridge Hello Time
:2
Bridge Max Age
:20
Root Port
:0
Root Path Cost
:0
Designated Root
:80:00:00:20:06:25:00:11
Designated Root Priority
:32768
Root Bridge Forward Delay
:15
Root Bridge Hello Time
:2
Root Bridge Max Age
:20
