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QSW-3900-24-SFP-AC
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Qtech QSW-3900-24-SFP-AC [197/245] Stp configuration

Qtech QSW-3900-48-SFP-DC [197/245] Stp configuration

QTECH Software Configuration Manual

15-196

15.1.2.3 How MSTP works

MSTP divides an entire Layer 2 network into multiple MST regions, which are interconnected by a

computed CST. Inside an MST region, multiple spanning trees are generated through computing, each spanning tree

called an MST instance. Among these MST instances, instance 0 is the IST, while all the others are MSTIs. Similar to

STP, MSTP uses configuration BPDUs to compute spanning trees. The only difference between the two protocols

being in that what is carried in an MSTP BPDU is the MSTP configuration on the device from which this BPDU is

sent.

1) CIST computing

By comparison of “configuration BPDUs”, the device with the highest priority is elected as the root bridge

of the CIST. MSTP generates an IST within each MST region through computing, and, at the same time, MSTP

regards each MST region as a single device and generates a CST among these MST regions through computing. The

CST and ISTs constitute the CIST of the entire network.

2) MSTI computing

Within an MST region, MSTP generates different MSTIs for different VLANs based on the

VLAN-to-instance mappings.

MSTP performs a separate computing process, which is similar to spanning tree computing in STP, for each

spanning tree.

In MSTP, a VLAN packet is forwarded along the following paths :

· Within an MST region, the packet is forwarded along the corresponding MSTI.

· Between two MST regions, the packet is forwarded along the CST.

15.1.2.4 Implementation of MSTP on devices

MSTP is compatible with STP and RSTP. STP and RSTP protocol packets can be recognized by devices

running MSTP and used for spanning tree computing.

In addition to basic MSTP functions, many management-facilitating special functions are provided, as

follows :

· Root bridge hold

· Root bridge backup

· Root guard

· BPDU guard

· Loop guard

· Support for hot swapping of interface cards and active/standby changeover.

15.1.3 Protocols and Standards

MSTP is documented in :

· IEEE 802.1D : Spanning Tree Protocol

· IEEE 802.1w : Rapid Spanning Tree Protocol

· IEEE 802.1s : Multiple Spanning Tree Protocol

15.2 STP Configuration

15.2.1 STP Configuration list

The configuration can be effective only after STP enables. Configure related parameter of devices or

Ethernet interface before enabling STP and these configurations will be saved after disabling STP. And the parameter

will be effective after re-enabling STP. STP configuration list is as following :

· Enable/disable interface STP

· Configure STP mode

Qtech QSW-3900-24-SFP-AC [197/245] Stp configuration

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