7-10
z
MSTP supports mapping VLANs to MST instances (MSTIs) by means of a VLAN-to-MSTI mapping
table. MSTP can reduce communication overheads and resource usage by mapping multiple
VLANs to one MSTI.
z
MSTP divides a switched network into multiple regions, each containing multiple spanning trees
that are independent of one another.
z
MSTP prunes a loop network into a loop-free tree, thus avoiding proliferation and endless cycling of
packets in a loop network. In addition, it provides multiple redundant paths for data forwarding, thus
supporting load balancing of VLAN data.
z
MSTP is compatible with STP and RSTP.
Basic concepts in MSTP
Figure 7-4
Basic concepts in MSTP
CST
Region A0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST
Region B0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST
Region C0
VLAN 1 mapped to instance 1
VLAN 2 and 3 mapped to
instance 2
Other VLANs mapped to CIST
Region D0
VLAN1 mapped to instance 1
B as regional root bridge
VLAN 2 mapped to instance 2
C as regional root bridge
Other VLANs mapped to CIST
BPDU
BPDU
BPDU
C
D
B
A
Assume that all bridges in
are running MSTP. This section explains some basic concepts of
MSTP.
1) MST
region
A multiple spanning tree region (MST region) consists of multiple bridges in a switched network and the
network segments among them. These bridges have the following characteristics:
z
All are MSTP-enabled,
z
They have the same region name,
z
They have the same VLAN-to-MSTI mapping configuration,
z
They have the same MSTP revision level configuration, and
