When you are preparing for the CCNP Switch (642-813) or BCMSN exam (642-812) there are quite a few topics which are important not only from the perspective of passing  the  “Implementing Cisco IP Switched Network” exam or BCMSN exam but also for the day to day network troubleshooting tasks.

One among the key topic is “spanning tree loop guard”. As the name itself suggests Loop Guard is a method used for ensuring no spanning tree protocol loops (STP) occurs in any network topology. Though STP loop guard feature can prevents STP loops as best it can, still chances of loops are there due to unidirectional link failure or congestions issues in the Cisco Switch. It’s always recommended, the loop guard feature to be used in conjunction with UDLD feature. I will cover about UDLD feature in one more article.

The basic function of loop guard feature is to prevent loops conservatively by preventing alternate or root ports from becoming DPs in the topology. If BPDUs are not received on a non-Designated Port, and Loop Guard is enabled, that port is moved into the STP loop-inconsistent Blocking state, instead of the Listening /Learning / Forwarding state.

Loop Guard operates only on ports that are considered point-to-point by the spanning tree, and it cannot be run in conjunction with Root Guard on an interface.

To enable Loop Guard on a Cisco Catalyst Switch, you can use the following IOS command in the global configuration mode

ITKE-3750-AS01(config)# spanning-tree loopguard default

I passed the “Implementing Cisco IP Switched Network”exam successfully couple of days back.  Now I am one step closer to achieving mp CCNP. My approach was simple and straight forward, I read the Cisco Press title CCNP SWITCH 642-813 Official Certification Guide. Thanks to Cisco Press and Jamie Adams for providing me a copy of CCNP Study guides. The exam was pretty easy but be careful there are few ambiguous questions which really needs your experience and expert knowledge on the topic.

I have following piece of advice for the CCNP aspirers

• 1) Set the date for exam before starting your preparations (Goal Setting).
• 2) Read Cisco Press title CCNP SWITCH 642-813 Official Certification Guide.
• 3) Practice the Boson questions came with the title CCNP SWITCH 642-813 Official Certification Guide.
• 4) Watch CBT nuggets if needed as they are really cool videos to watch.
• 5) Practice labs, (create your own scenarios on STP, HRSP, VTP, VRRP, GLBP etc.) If you can afford get three Cisco 3550 Series Switches from eBay.
• 6) A week before exam review all the topics and practice few labs and boson practice test.

(My CCNP Switch Lab)

If you follow the above with dedication and determination nothing can stop you from achieving CCNP.