MSTP is an enhancement to RSTP and is the preferred spanning tree protocol for the BIG-IP® system. MSTP is specifically designed to understand VLANs and VLAN
tagging (specified in IEEE 802.1q). Unlike STP and RSTP, which allow only one spanning tree
instance per system, MSTP allows multiple spanning tree instances. Each instance corresponds to a
spanning tree, and can control one or more VLANs that you specify when you create the instance.
Thus, for any BIG-IP system interface that you assigned to multiple VLANs, MSTP can block a path
on one VLAN, while still keeping a path in another VLAN open for traffic. Neither STP nor RSTP
has this capability.
A unique feature of MSTP is the concept of spanning tree regions. A
is a logical set of bridges on the network that share the same values for certain
MSTP configuration settings. These configuration settings are: The MSTP configuration name, the
MSTP configuration number, the instance numbers, and the VLAN members of each instance. When the
values of these settings are identical on two or more bridges, the spanning tree algorithm
considers these bridges to constitute an MSTP region. An MSTP region indicates to the spanning
tree algorithm that it can use MSTP for all bridges in that region, and thus take VLANs into
account when blocking and unblocking redundant paths.
You do not explicitly create a region. The spanning tree algorithm automatically groups bridges into regions, based on the values you assign to the MSTP configuration name, revision number, instance numbers, and instance members.
MSTP can only operate on bridges that are within a region. However, if the BIG-IP system connects to a bridge in a different MSTP region or outside of an MSTP region, the system still participates in spanning tree. In this case, the system is part of the spanning tree instance 0, also known as the Common and Internal Spanning Tree (CIST).
BIG-IP systems released prior to version 9.0 do not support MSTP.