Avaya 8600 Configuration Manual page 32

Link aggregation fundamentals
network failure, do not break or remove an MSTP device chain before you disable SMLT
interoperability.
Assumptions:
• All bridges in the network have a bridge identifier greater than 00:00:00:00:00:00:00:02.
General limitations:
• The SMLT cluster always acts as the Root Bridge within the MSTP domain. For MSTP,
the SMLT Cluster is the CIST Regional Root, CIST Root, and MSTI Root for all MSTI
instances.
• Only 1 SMLT cluster can participate in the MSTP domain: if more than one cluster tries
to participate each advertises the same Root Bridge ID and a conflict occurs.
• No link or MLT connected in parallel to the IST MLT is supported.
• SMLT and SLT links cannot run MSTP.
• Only MSTP modes are supported for SMLT Interoperability.
• You must enable SMLT Interoperability on both switches forming the SMLT cluster. Layer
2 loops form if you enable SMLT Interoperability on only 1 member of the SMLT cluster.
To ensure that one of the switches forming the SMLT Cluster is always the Root bridge, when
you enable SMLT Interoperability the system automatically assigns MSTP Bridge IDs
00:00:00:00:00:00:00:01 and 00:00:00:00:00:00:00:02.
With MSTP, and based on VLAN membership, physical ports can belong to multiple MSTP
instances (CIST + 0 or more MSTIs). When you enable SMLT Interoperability with MSTP,
because all VLANs are q-tagged over the IST link, the system enables STP on the IST and
sets the PathCost to 1 across all MSTP instances.
MSTP does not allocate a Bridge MAC for MSTI instances; a MAC is allocated only for the
Base CIST. But the system can set Bridge Priority values for MSTI instances. So, for MSTP
operation with SMLT Interoperability, the system changes the CIST Base MAC to
00:00:00:00:00:01 and 00:00:00:00:00:02, like the RSTP implementation, while the system
sets the Bridge Priority to 00:00 across all instances (CIST & any MSTIs).
When you activate SMLT Interoperability with MSTP, the following list summarizes what
happens automatically for all MSTP instances (CIST/MSTIs):
• STP is enabled on the IST ports for all instances.
• STP PathCost is set to 1 on IST ports for all instances.
• The STP Bridge Priority is set to 00:00 for all instances.
• The MSTP Base MAC is set to 00:00:00:00:00:01 on the switch with the highest IST IP
(SMLT master).
• The SMLT master is always the CIST Root + Regional Root + MSTI Root.
• The RSTP Base MAC is set to 00:00:00:00:00:02 on the switch with the lowest IST IP
(SMLT slave).
• The SMLT slave is always the CIST/Regional/MSTI Root if the SMLT master IST peer
fails.
32 Configuration — Link Aggregation, MLT, and SMLT
Comments? infodev@avaya.com
January 2012