Qtech QSW-2900-24T-AC [149/209] In rstp a newly elected designated port can enter the forwarding 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 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

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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 reach the final topology stability.

& Note:

l 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.

l In RSTP, a newly elected designated port can enter the forwarding 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 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.

Although RSTP support 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 VLANs, and the packets of all

VLANs are forwarded along the same spanning tree.

2) 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. For description about VLANs, refer to

VLAN Configuration in the Access Volume.

MSTP features the following:

· MSTP supports mapping VLANs to MST instances by means of a VLAN-to-instance mapping table.

· MSTP divides a switched network into multiple regions, each containing multiple spanning trees that are

independent of one another.

· MSTP prunes loop networks into a loop-free tree, thus avoiding proliferation and endless recycling of

packets in a loop network. In addition, it provides multiple redundant paths for data forwarding, thus

supporting load balancing of VLAN data in the data forwarding process.

· MSTP is compatible with STP and RSTP.

b) VI. Some concepts in MSTP

As shown in Figure 4, there are four multiple spanning tree (MST) regions, each made up of four switches

running MSTP. In light with the diagram, the following paragraphs will present some concepts of MSTP.