Information Technology Reference
In-Depth Information
show spanning-tree
show bridge
show processes cpu
debug spantree
logging buffered
Catalyst OS Commands
show port
show mac
show spantree
show spantree statistics
show spantree blockedports
show spantree summary
show top
show inband/show biga
show system
show counters
set spantree root [secondary]
set spantree uplinkfast
set logging level
set logging buffered
Designing STP to Avoid Trouble
We have seen that the spanning tree can fail in some few circumstances and that troubleshooting the
related issues can be quite difficult in a live network. This part introduces some guidelines to reduce the
risks associated with the spanning tree.
Know Where the Root Is
It sounds trivial, but very often the information is not available at troubleshooting time. Don't leave the
STP to decide which bridge will be root. Depending on the design of the network, you should be able to
identify for each VLAN which switch is well suited to be root. Generally, it is good to choose a powerful
bridge in the middle of the network. Putting the root bridge in the center of the network, directly
connected to the servers and routers, generally reduces the average distance from the clients to the
servers and routers.
In Figure 23-13, you can clearly see that if Bridge B is the root, the link from A to C will be blocked on
A or C. In this case, hosts connected to switch B can access the server and the router in two hops, and
hosts connected to Bridge C in three hops. That makes an average of 2.5 hops.
If Bridge A is the root, the router and the server are reachable in two hops for both hosts connected on
B and C. The average distance to them is now two hops.
