Figure 2-12 Loop Networking With Stp - Raisecom ISCOM2600G-HI (A) Series Configuration Manual

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ISCOM2600G-HI (A) Series Configuration Guide

Figure 2-12 Loop networking with STP

Although STP can eliminate loop network and prevent broadcast storm well, its shortcomings
are still gradually exposed with thorough application and development of network technology.
The major disadvantage of STP is the slow convergence speed.
RSTP
For improving the slow convergent speed of STP, IEEE 802.1w establishes Rapid Spanning
Tree Protocol (RSTP), which increases the mechanism to change interface blocking state to
forwarding state, speed up the topology convergence rate.
The purpose of STP/RSTP is to simplify a bridged LAN to a unitary spanning tree in logical
topology and to avoid broadcast storm.
The disadvantages of STP/RSTP are exposed with the rapid development of VLAN
technology. The unitary spanning tree simplified from STP/RSTP leads to the following
problems:
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The whole switching network has only one spanning tree, which will lead to longer
convergence time on a larger network.
After a link is blocked, it does not carry traffic any more, causing waste of bandwidth.
Packet of partial VLAN cannot be forwarded when network structure is unsymmetrical.
As shown in Figure 2-13, Switch B is the root switch; RSTP blocks the link between
Switch A and Switch C logically and makes that the VLAN 100 packet cannot be
transmitted and Switch A and Switch C cannot communicate.
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