Design Reference

Table Of Contents
Use MSTP to configure MSTIs on the same switch. Each MSTI can include one or more
VLANs.
In MSTP mode you can configure up to 64 instances. Instance 0 or Common and Internal
Spanning Tree (CIST) is the default group, which includes default VLAN 1. Instances 1 to 63
are MSTIs.
RSTP and MSTP provide a global spanning tree parameter, called version, for backward
compatibility with legacy STP. You can configure version to either STP-compatible mode,
RSTP mode, or MSTP mode:
An STP-compatible port transmits and receives only STP Bridge Protocol Data Units
(BPDU). An RSTP or MSTP BPDU that the port receives in this mode is discarded.
An RSTP or MSTP port transmits and receives only RSTP or MSTP BPDUs. If an RSTP
or MSTP port receives an STP BPDU, it becomes an STP port. You must manually
intervene to configure this port for RSTP or MSTP mode again. This process is called
Port Protocol Migration.
You must be aware of the following recommendations before you implement MSTP or RSTP:
The default mode is MSTP. A special boot configuration flag identifies the mode.
You can lose your configuration if you change the spanning tree mode from MSTP to
RSTP and the configuration file contains VLANs configured with MSTI greater than 0.
RSTP only supports VLANs configured with the default instance 0.
For best interoperability results, contact your Avaya representative.
MSTP and RSTP considerations
Network Design Reference for Avaya VSP 4000 February 2014 53