![background image](http://html1.mh-extra.com/html/cts/fos-3124-series/fos-3124-series_user-manual_2694076071.webp)
71
2.6.19 Spanning Tree Command
The Spanning Tree Protocol (STP), defined in the IEEE Standard 802.1D, creates a
spanning tree within a mesh network of connected layer-2 bridges (typically Ethernet
switches) and disables the links which are not part of that tree, leaving a single active path
between any two network nodes.
Multiple active paths between network nodes cause a bridge loop. Bridge loops create
several problems. First, the MAC address table used by the switch or bridge can fail, since
the same MAC addresses (and hence the same network hosts) are seen on multiple ports.
Second, a broadcast storm occurs. This is caused by broadcast packets being forwarded in
an endless loop between switches. A broadcast storm can consume all available CPU
resources and bandwidth.
Spanning tree allows a network design to include spare (redundant) links to provide
automatic backup paths if an active link fails, without the danger of bridge loops, or the need
for manually enabling/disabling these backup links.
To provide faster spanning tree convergence after a topology change, an evolution of the
Spanning Tree Protocol: Rapid Spanning Tree Protocol (RSTP), introduced by IEEE with
document 802.1w. RSTP is a refinement of STP; therefore, it shares most of its basic
operation characteristics. This essentially creates a cascading effect away from the root
bridge where each designated bridge proposes to its neighbors to determine if it can make a
rapid transition. This is one of the major elements which allow RSTP to achieve faster
convergence times than STP.
Spanning-tree command
Parameter
Description
Switch(config)# spanning-
tree aggregated-port
Enable Spanning Tree Protocl function
on aggregated ports.
Switch(config)# spanning-
tree aggregated-port cost [1-
200000000]
[1-200000000] Specify aggregated ports
‟ path cost.
Switch(config)# spanning-
tree aggregated-port priority
[0-240]
[0-240]
Specify aggregated ports
‟ priority.
Switch(config)# spanning-
tree aggregated-port edge
Enable aggregated ports to shift to
forwarding state when the link is up.
If you know a port is directly connected
to an end device (that doesn't support
RSTP) then set it as an edge port to
ensure maximum performance. This will
tell the switch to immediately start
forwarding traffic on the port and not
bother trying to establish a RSTP
connection. Otherwise, turn it off.
Summary of Contents for FOS-3124 SERIES
Page 202: ...202 Restart DHCP service ...