4000 Router Series Layer 2 - LAN Switching Configuration Guide

• legacy—Compatible format

When the number of existing MSTIs exceeds 48, the port can send only 802.1s MSTP packets.

By default, the packet format recognition mode of a port is auto. The port automatically distinguishes the

two MSTP packet formats, and determines the format of packets that it will send based on the recognized

format.

You can configure the MSTP packet format on a port. When operating in MSTP mode after the

configuration, the port sends only MSTP packets of the format that you have configured to communicate

with devices that send packets of the same format.

A port in auto mode sends 802.1s MSTP packets by default. When the port receives an MSTP packet of

a legacy format, the port starts to send packets only of the legacy format. This prevents the port from

frequently changing the format of sent packets. To configure the port to send 802.1s MSTP packets, shut

down and then bring up the port.

To configure the MSTP packet format to be supported on a port:

Step Command Remarks

1. Enter system view.

system-view N/A

2. Enter Layer 2 Ethernet

interface view.

interface interface-type interface-number N/A

3. Configure the mode that the

port uses to recognize/send

MSTP packets.

stp compliance { auto | dot1s | legacy } The default setting is auto.

Enabling outputting port state transition information

In a large-scale spanning tree network, you can enable devices to output the port state transition

information of all MSTIs or the specified MSTI in order to monitor the port states in real time.

To enable outputting port state transition information:

Step Command Remarks

1. Enter system view.

system-view N/A

2. Enable outputting port state

transition information.

• In STP/RSTP mode:

stp port-log instance 0

• In MSTP mode:

stp port-log instance { instance-list |

all }

By default, this function is

enabled.

Enabling the spanning tree feature

You must enable the spanning tree feature for the device before any other spanning tree related

configurations can take effect. Make sure the spanning tree feature is enabled globally and on the

desired ports.

You can disable the spanning tree feature for certain ports with the undo stp enable command to exclude

them from spanning tree calculation and save CPU resources of the device.