Multiple Spanning Tree Protocol (Ieee 802.1S) - Symbol ES3000 Manual

5-5
Spanning Tree Protocols
reconfiguration. Point-to-point link ports are ports that connect to another switch. Point-to-point links
are reconfigured with a proposal-agreement dialog that is much faster than rebuilding the entire
spanning tree.
If an RSTP-enabled switch is connected to a switch that cannot communicate using RSTP BPDUs, the
RSTP-enabled switch will communicate with the legacy switch using STP BPDUs. The spanning tree
will still reconfigure successfully, but it will do so much more slowly than it would if only RSTP-
enabled switches were connected. If possible, make sure that all the switches in a spanning-tree
domain are of one type or another, not a mix.

5.4.1 Multiple Spanning Tree Protocol (IEEE 802.1S)

Multiple Spanning Tree Protocol (MSTP) allows the creation of multiple spanning tree domains. Each
spanning tree instance provides the same advantages as the regular Spanning tree - however now
the network administrator can utilize the links in the network to their fullest. Load balancing spreads
the traffic across the multiple paths, improving performance. MSTP also deals properly with VLANS
that cross switch boundaries. MSTP is compatible with RSTP. MSTP uses a modified RSTP for rapid
convergence of spanning tree data.
MSTP spanning trees are also called MSTP instances. MSTP instances are grouped together into
MSTP configurations, also known as MSTP regions.
Each MSTP configuration consists of one or more MSTP instances. An MSTP configuration has a
number, a name, and a revision level. The MSTP instances within an MSTP configuration must share
protocol timing values - Hello Time, Maximum Age, and Forward Delay. A given switch may only be
part of one MSTP configuration.
Each MSTP instance is a spanning tree, but its members are VLANs rather than switches. The MSTP
instance may have one or more VLANs. A given VLAN may only participate in one MSTP instance.
Each MSTP configuration will have an instance root and the instance root will store the internal
spanning tree (IST) for the MSTP configuration. The MSTP configurations will communicate and
establish a common spanning tree (CST) which maps forwarding path information between the
different MSTP configurations. The combination of the common spanning tree and internal spanning
trees is called the common and internal spanning tree or CIST.