STP instability

[rehansami]

How can we detect unexpected states of STP on a particular network consisting of 4 swtiches keeping in view that the topolgy of the netwrok is unchanged.

The problem actually has occured in the 196.1.65.xxx network of our college. Four switches , each with redundant links (one 100 Mbps and one 1Gbps link) are connected. Three of the switches are connected to the main switch via 1Gbps link and there 100 Mbps links are connected to the fourth switch. On all switches the STP is enabled asusual but the state of the protocol is unstable.

Please let me know how to detect the fault and reach to a possible solution.

[Prashanth Krishnappa]

Your posting does not describe the exact issue you had. The following page should help you in troubleshooting STP issues

http://www.cisco.com/warp/public/473/16.html

http://www.cisco.com/warp/public/473/#SpanningTree

http://www.cisco.com/warp/public/473/103.html#stp

[jhalldn]

Perhaps you should consider to use SNMP TRAPS and LOGGING from your switches. Enable this features and check the logs for information. Every time a change is made with in your STP domain, a trap will be send.

Otherwise start debug in a switch..debug spanning-tree

If you dont have SPANNING-TREE PORTFAST enabled on user ports, the STP will its algotrim because the topology is changed every time a computer reboots/shutdown/starts.

[lakn]

you could see if the command

spanning-tree vlan 1,10,20,30,40,50,60,70,201 priority 8192

or

spanning-tree root guard

should do on your main-switch

That should keep the STP from converging to much. Beware that it makes the switch "master" in the vlans given.