Operation Manual – MSTP
H3C S3100 Series Ethernet Switches Chapter 1 MSTP Configuration
1-11
Note:
z In RSTP, the state of a root port can transit fast under the following conditions: the
old root port on the device has stopped forwarding data and the upstream
designated port has started forwarding data.
z In RSTP, the state of a designated port can transit fast under the following
conditions: the designated port is an edge port or a port connected with a
point-to-point link. If the designated port 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 forwarding state immediately after the device undergoes handshake with
the downstream device and gets a response.
RSTP supports rapid convergence. Like STP, it is of the following disadvantages: all
bridges in a LAN are on the same spanning tree; redundant links cannot be blocked by
VLAN; the packets of all VLANs are forwarded along the same spanning tree.
II. Features of MSTP
The multiple spanning tree protocol (MSTP) overcomes the shortcomings of STP and
RSTP. In addition to support for rapid network convergence, it also allows data flows of
different VLANs to be forwarded along their own paths, thus providing a better load
sharing mechanism for redundant links.
MSTP features the following:
z MSTP supports mapping VLANs to MST instances by means of a
VLAN-to-instance mapping table. MSTP introduces “instance” (integrates multiple
VLANs into a set) and can bind multiple VLANs to an instance, thus saving
communication overhead and improving resource utilization.
z MSTP divides a switched network into multiple regions, each containing multiple
spanning trees that are independent of one another.
z MSTP prunes a ring network into a network with tree topology, preventing packets
from being duplicated and forwarded in a network endlessly. Furthermore, it offers
multiple redundant paths for forwarding data, and thus achieves load balancing for
forwarding VLAN data.
z MSTP is compatible with STP and RSTP.
1.2.2 Basic MSTP Terminologies
Figure 1-4 illustrates basic MSTP terms (assuming that MSTP is enabled on each
switch in this figure).
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