Port Path Cost; Simple Stp Configuration - Lenovo ThinkSystem NE2552E Application Manual

Port Path Cost

Simple STP Configuration

178
NE2552E Application Guide for ENOS 8.4
The port path cost assigns lower values to high‐bandwidth ports, such as 10
Gigabit Ethernet, to encourage their use. The cost of a port also depends on
whether the port operates at full‐duplex (lower cost) or half‐duplex (higher cost).
For example, if a 100‐Mbps (Fast Ethernet) link has a "cost" of 10 in half‐duplex
mode, it will have a cost of 5 in full‐duplex mode. The objective is to use the fastest
links so that the route with the lowest cost is chosen. A value of 0 (the default)
indicates that the default cost will be computed for an auto‐negotiated link or LAG
speed.
Use the following command to modify the port path cost:
NE2552E(config)# interface port <port>
NE2552E(config-if)# spanning-tree stp <STP instance or range> path-cost <path cost
value>
NE2552E(config-if)# exit
The port path cost can be a value from 1 to 200000000. Specify 0 for automatic path
cost.
Figure 11 depicts a simple topology using a switch‐to‐switch link between two
switches (via either external ports or internal Inter‐Switch Links).
Figure 11. Spanning Tree Blocking a Switch‐to‐Switch Link
Enterprise
Routing
Switches
Switch 1
Server
x
STP
Blocks Link
Server Server
Switch 2
Server