HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 223

Information About MST MST Configuration Information that one BPDU that the IST sends. Because the MST BPDU carries information for all instances, the number of BPDUs that need to be processed to support MSTIs is significantly reduced. Figure 27: MST BPDU with M-Records for MSTIs MST Configuration Information The MST configuration that must be identical on all switches within a single MST region is configured by the user. You can configure the following three parameters of the MST configuration: • Name-32-character string, null padded and null terminated, identifying the MST region • Revision number-Unsigned 16-bit number that identifies the revision of the current MST configuration Note You must set the revision number when required as part of the MST configuration. The revision number is not incremented automatically each time that the MST configuration is committed. • MST configuration table-4096-element table that associates each of the potential 4094 VLANs supported to a given instance with the first (0) and last element (4095) set to 0. The value of element number X represents the instance to which VLAN X is mapped. Caution When you change the VLAN-to-MSTI mapping, the system restarts MST. MST BPDUs contain these three configuration parameters. An MST bridge accepts an MST BPDU into its own region only if these three configuration parameters match exactly. If one configuration attribute differs, the MST bridge considers the BPDU to be from another MST region. IST, CIST, and CST IST, CIST, and CST Overview Unlike Rapid PVST+, in which all the STP instances are independent, MST establishes and maintains IST, CIST, and CST spanning trees, as follows: OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 177