Port Path Cost; Simple Stp Configuration - Lenovo Flex System Fabric CN4093 Application Manual

Port Path Cost

Simple STP Configuration

176
CN4093 Application Guide for N/OS 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:
CN 4093(config)# interface port <port alias or number>
CN 4093(config-if)# spanning-tree stp <1‐128> path-cost <path cost value>
CN 4093(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