Operation Manual
95
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
fortrafcwithintheregionforanyVLANsnotcovered
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.