EnGenius EWS Series User Manual page 109

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 traffic 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.
Enter the information to set up CIST for the Switch:
Root Address Displays the root bridge MAC address. Root in root bridge refers to the base of
the spanning tree, which the Switch could be configured for.
Priority Displays the priority for the bridge. When switches are running STP, each is
assigned a priority. After exchanging BPDUs, the Switch with the lowest priority
value becomes the root bridge.
Forward Delay Displays the Switch Forward Delay Time. This is the time (in seconds) the root
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