Operation Manual

42
Spanning Tree Loops
Loops occur when alternate routes exist between hosts.
Loops in an extended network can cause the Switch
toforwardtrafcindenitely,resultinginincreased
trafcandreducingnetworkefciency.OncetheSTP
isenabledandcongured,primarylinksareestablished
and duplicated links are blocked automatically. The
reactivation of the blocked links is also accomplished
automatically. STP provides a tree topology and other
Spanning tree versions supported include STP, Multiple
Spanning Tree Protocol (MSTP), and Rapid Spanning Tree
Protocol (RSTP). Please note that only one spanning
tree can be active on the Switch at a time. The default
setting is: RSTP.
STP: Select whether to Enable or Disable the
spanning tree operation on the Switch.
Force Version:
Select the Force Protocol Version parameter
for the Switch.
• STP (Spanning Tree Protocol) - IEEE
802.1D.
• RSTP (Rapid Spanning Tree Protocol) - IEEE
802.1w.
• MSTP (Multiple Spanning Tree Protocol) -
IEEE802.1s.
MultipleSpanningTreeProtocol(MSTP)denedinIEEE
802.1s,enablesmultipleVLANstobemappedtoredu-
cethe number of spanning-tree instances needed to sup-
port a large number of VLANs. If there is only one VLAN
in the network, a single STP works appropriately.
If the network contains more than one VLAN however,
thelogicalnetworkconguredbyasingleSTPwould
work,butitbecomesmoreefcenttousethealternate
paths available by using an alternate spanning tree for
different VLANs or groups of VLANs. MSTP (which is
based on RSTP for fast convergence) is designed to sup-
port independent spanning trees based on VLAN groups.
MSTPprovidesmultipleforwardingpathsfordatatrafc
and enables load balancing.
STP and RSTP prevent loops from forming by ensuring
that only one path exists between the end nodes in your
network. RSTP is designed as a general replacement for
the slower, legacy STP. RSTP is also incorporated into
MSTP. With STP, convergence can take up to a minute to
complete in a larger network. This can result in the loss
of communication between various parts of the network
during the convergence process so STP can subsequent-
ly can lose data packets during transmission.