Operation Manual

48
CIST Instance Settings
The Common Instance Spanning Tree (CIST) protocol is
formed by the spanning-tree algorithm running among
bridgesthatsupporttheIEEE802.1w,IEEE802.1s,and
IEEE802.1Dstandard.ACommonandInternalSpanning
Tree (CIST) represents the connectivity of the entire
network and it is equivalent to a spanning tree in an STP/
RSTP.
The CIST inside a Multiple Spanning Tree Instance
(MST) region is the same as the CST outside a region.
All regions are bound together using a CIST, which
is responsible for creating loop-free topology across
regions, whereas the MSTI controls topology inside
regions. CST instances allow different regions to
communicate between themselves. CST is also used for
trafcwithintheregionforanyVLANsnotcoveredbya
MSTI. In an MSTP-enabled network, there is only one CIST
that runs between MST regions and single spanning tree
devices. A network may contain multiple MST regions and
other network segments running RSTP. Multiple regions
and other STP bridges are interconnected using a single
CST.