Multiple Instance Spanning-Tree Operation

Overview

Note on Path Cost RSTP and MSTP implements a greater range of path costs and new default path cost values to account for higher network speeds. These values are different than the values defined by 802.1D STP as shown below.

Port Type

802.1D STP Path Cost

RSTP and MSTP Path Cost

10 Mbps

100

2 000 000

100 Mbps

10

200 000

1 Gbps

5

20 000

 

 

 

Because the maximum value for the path cost allowed by 802.1D STP is 65535, devices running that version of spanning tree cannot be configured to match the values defined by MSTP, at least for 10 Mbps and 100 Mbps ports. In LANs where there is a mix of devices running 802.1D STP, RSTP, and/or MSTP, you should reconfigure the devices so the path costs match for ports with the same network speeds.

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