R3166-R3206-HP High-End Firewalls Network Management Configuration Guide-6PW101

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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.
The Rapid Spanning Tree Protocol (RSTP) is an optimized version of STP. RSTP allows a newly elected root
port or designated port to enter the forwarding state much quicker under certain conditions than in STP.
As a result, it takes a shorter time for the network to converge.
NOTE:
• In RSTP, a newly elected root port can enter the forwarding state rapidly if this condition is met: The old
root port on the device has stopped forwarding data and the upstream designated port has started
forwarding data.
• In RSTP, a newly elected designated port can enter the forwardin
g
state rapidly if this condition is met:
The designated port is an edge port or a port connected with a point-to-point link. If the desi
g
nated por
t
is an edge port, it can enter the forwarding state directly; if the designated port is connected with a
point-to-point link, it can enter the forwardin
g
state immediately after the device under
g
oes handshake
with the downstream device and gets a response.
Although RSTP supports rapid network convergence, it has the same drawback as STP does: 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 shortcomings 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, thus providing a better load sharing mechanism for redundant links.
MSTP features the following:
• 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, 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.
• MSTP is compatible with STP and RSTP.
Basic concepts in MSTP
Assume that all the four devices in Figure 28 are running MSTP. This section explains some basic
concepts of MSTP based on the figure.