How to prevent spantree loops in Cisco Switches?

Question

I want to make sure that I don't get a spann-tree loop on two ports between two switches. Will one automatically block while the other forwards. How can I make sure?

Answer 1

http://www.cisco.com/warp/public/473/5.html

You can also issue the set spantree portfast command, on a per-port basis. When you enable the portfast variable on a port, the port immediately switches from blocking mode to forwarding mode. Enablement of portfast helps to prevent timeouts on clients who use Novell Netware or use DHCP in order to obtain an IP address. However, do not use this command when you have switch-to-switch connection. In this case, the command can result in a loop. The 30- to 60-second delay that occurs during the transition from blocking to forwarding mode prevents a temporal loop condition in the network when you connect two switches.

Leave most other STP variables at their default values.