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DES-7200 Configuration Guide Chapter 10 MSTP Configuration
10-7
Figure-7
10.1.1.7 Rapid Convergence of RSTP
The following introduces the special function of RSTP: enabling rapid
forwarding on a port.
The STP protocol will forward packets after 30s since the port roles are selected,
which is twice as the Forward-Delay Time (you can set the Forward-Delay Time,
which is 15s by default). Furthermore, the root port and designated port of each
bridge will carry out the forwarding again after 30s, so it will take about 50s to
stabilize the tree-type structure of the whole network topology.
The forwarding procedure of the RSTP protocol is different from that of the STP
protocol. As shown in Figure 8, Switch A sends the specific proposal message
of the RSTP protocol. Switch B detects that the priority of Switch A is higher
than itself, takes the Switch A as the root bridge and the port that receives the
message as the root port and forwards the proposal message. Then it sends
the Agree message to Switch A through the root port. Upon the receipt of the
proposal message, Switch A will forward the message through its designated
port. After that, Switch sends the proposal message through the designated port
to extend the spanning tree in turn. In theory, the RSTP protocol can
immediately restore the tree-type network structure to implement rapid
convergence when the network topology changes.