802.1s Multiple Spanning Tree Protocol (MSTP)
incompatibility between devices running the older 802.1D STP and your switch running MSTP or RSTP. Please see the “Note on Path Cost” on page
Tips for Planning an MSTP Application
■Ensure that the VLAN configuration in your network supports all of the forwarding paths necessary for the desired connectivity. All ports con necting one switch to another within a region and one switch to another between regions should be configured as members of all VLANs config ured in the region.
■All ports or trunks connecting one switch to another within a region should be configured as members of all VLANs in the region. Otherwise, some VLANs could be blocked from access to the
■Plan individual regions based on VLAN groupings. That is, plan on all MSTP switches in a given region supporting the same set of VLANs. Within each region, determine the VLAN membership for each
■There is one logical
■
■
•Any
•Any IST or MST instance within a region
•Any legacy (802.1D or 802.1w) switch or group of switches. (Where multiple paths exist between an MST region and a legacy switch, expect the CST to block all but one such path.)
Determine the root bridge and root port for each instance.
Determine the designated bridge and designated port for each LAN seg ment.
■Determine which VLANs to assign to each instance, and use port trunks with 802.1Q VLAN tagging where separate links for separate VLANs would result in a blocked link preventing communication between nodes on the same VLAN. (Refer to “MSTP Operation with 802.1Q VLANs” on page
■Identify the edge ports connected to end nodes and enable the