Configuration Guide MSTP Configuration
Compatibility of RSTP and STP
The RSTP protocol is completely compatible with the STP protocol. It will judge
whether the connected bridge supports the STP protocol or the RSTP protocol
by the version number of the received BPDU message automatically. Only the
forwarding process of the STP protocol is executed in the case of that the
bridge supports the STP protocol. This cannot maximize the performance of the
RSTP protocol.
Furthermore, using the RSTP protocol and the STP protocol will cause a
problem. As shown in Figure 17-12, Switch A supports the RSTP protocol, while
Switch B supports the STP protocol. Both switches are connected with each
other. Switch A will send the STP BPDU message to Switch B for compatibility.
However, if Switch A is connected with the RSTP-enabled Switch C, Switch A
still sends the STP BPDU message, and thus causing that Switch C considers
Switch A a STP-enabled bridge. As a result, two RSTP-supported switches run
the STP protocol, reducing their efficiency greatly.
For this reason, the RSTP protocol provides the protocol-migration function to
send the RSTP BPDU message forcibly in case that the peer bridge must
support RSTP. In this way, Switch C will detect the bridge connected with it
supports the RSTP protocol, so both two devices can run the RSTP protocol as
shown in Figure 13.
Figure-12 Protocol Migration
Figure-13
MSTP Overview
Ruijie series supports the MSTP protocol, a new spanning-tree protocol derived
from the traditional STP and RSTP protocols that includes the rapid forwarding
mechanism of the RSTP protocol itself.
Since traditional spanning tree protocols are not related to a VLAN, the
following problems may occur in a specific network topology.
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