System information

Publication date: Feb., 2012
Revision A1
- 187 -
CLIReferenceGuide
Copyright @ 2012 by Amer Networks
Chapter 43 STPCommandsofCLI
STP
The Spanning Tree Protocol (STP) can be used to detect and disabl e
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‐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, it enables all root ports and
designated ports, and disables all other ports. Network packets are
therefore only forwarded 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.

Table 42: STP Commands
Command Function
CName
Set MSTP Configuration name
FwdDelay
Set FwdDelay
MaxAge
Set Maxage
MaxHops
Set MaxHops
Statistics
Clear STP port statistics
Txhold
Set TxHold
Version
Set force-version
bpduFilter
Set edge port BPDU Filtering
bpduGuard
Set edge port BPDU Guard
migrate-check
Set the STP mCheck (Migration Check) variable for ports