H3C Technologies H3C SecPath F1000-E - Manual (Page 89)

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Introduction to MSTP
Why MSTP
STP and RSTP limitations
STP does not support rapid state transition of ports. A newly elected root port or designated port must
wait twice the forward delay time before transiting to the forwarding state, even if it is a port on a
point-to-point link or an edge port, which directly connects to a user terminal rather than to another
device or a shared LAN segment.
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.
Features of MSTP
Developed based on IEEE 802.1s, MSTP overcomes the limitations of STP and RSTP. In addition to the
support for rapid network convergence, it also allows data flows of different VLANs to be forwarded
along separate paths, providing a better load sharing mechanism for redundant links.
MSTP includes the following features:
• 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.
• 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.