H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 59)

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MSTP
STP and RSTP limitations
STP does not support rapid state transition of ports. A newly elected port must wait twice the forward
delay time before transiting to the forwarding state, even if it connects to a point-to-point link or is an
edge port.
Although RSTP supports rapid network convergence, it has the same drawback as STP—All bridges
within a LAN share the same spanning tree, so redundant links cannot be blocked based on VLAN, and
the packets of all VLANs are forwarded along the same spanning tree.
MSTP features
Developed based on IEEE 802.1s, MSTP overcomes the limitations of STP and RSTP. In addition to
supporting rapid network convergence, it also provides a better load sharing mechanism for redundant
links by allowing data flows of different VLANs to be forwarded along separate paths.
MSTP includes the following features:
• MSTP supports mapping VLANs to spanning tree instances by means of a VLAN-to-instance
mapping table. MSTP can reduce communication overheads and resource usage by mapping
multiple VLANs to one instance.
• MSTP divides a switched network into multiple regions, each containing multiple spanning trees
that are independent of one another.
• MSTP prunes a loop network into a loop-free tree, avoiding proliferation and endless cycling of
packets in a loop network. In addition, it provides multiple redundant paths for data forwarding,
supporting load balancing of VLAN data.
• MSTP is compatible with STP and RSTP.
MSTP basic concepts
Figure 13 shows a switched network that comprises four MST regions, each MST region comprising four
MSTP devices. Figure 14 shows the networking topology of MST region 3. This section describes some
basic concepts of MSTP.