Computer Software

Whether you’re working on your CCNA or CCNP, Cisco certification exams are the most demanding computer certification exams in the IT field. Cisco exams are not a test of memorization, they’re a test of your analytical skills. You’ll need to look at configurations and console output and analyze them to identify problems and answer detailed questions. To pass these demanding exams, you’ve got to truly understand how Cisco routers and switches operate – and the key to doing so is right in front of you.

The debug command.

Of course, there is no single “debug” command. Using IOS Help, you can quickly see that there are hundreds of these debugs, and I want to mention immediately that you should never practice these commands on a production router. This is one major reason you need to get some hands-on experience with Cisco products in a home lab or rack rental. No software program or “simulator” is going to give you the debug practice you need.

Now, why am I so insistent that you use debugs? Because that’s how you actually see what’s going on. It’s not enough to type a frame relay LMI command, you have to be able to see the LMIs being exchanged with “debug frame lmi”. You don’t want to just type a few network numbers in after enabling RIP, you want to see the routes being advertised along with their metrics with “debug ip rip”. The list goes on and on.

By using debugs as part of your CCNA and CCNP studies, you’re going beyond just memorizing commands and thinking you understand everything that’s happening when you enter a command or two. You move to a higher level of understanding how routers, switches, and protocols work — and that is the true goal of earning your CCNA and CCNP.

When you’re studying for the CCNP certification, especially the BSCI exam, you must gain a solid understanding of BGP. BGP isn’t just one of the biggest topics on the BSCI exam, it’s one of the largest. BGP has a great many details that must be mastered for BSCI success, and those of you with one eye on the CCIE must learn the fundamentals of BGP now in order to build on those fundamentals at a later time.

Path attributes are a unique feature of BGP. With interior gateway protocols such as OSPF and EIGRP, administrative distance is used as a tiebreaker when two routes to the same destination had different next-hop IP addresses but the same prefix length. BGP uses path attributes to make this choice.

The first attribute considered by BGP is weight. Weight is a Cisco-proprietary BGP attribute, so if you’re working in a multivendor environment you should work with another attribute to influence path selection.

The weight attribute is significant only to the router on which it is changed. If you set a higher weight for a particular route in order to give it preference (a higher weight is preferred over a lower one), that weight is not advertised to other routers.

BGP uses categories such as “transitive”, “non-transitive”, “mandatory”, and “optional” to classify attributes. Since weight is a locally significant Cisco-proprietary attribute, it does not all into any of these categories.

The weight can be changed on a single route via a route-map, or it can be set for a different weight for all routes received from a given neighbor. To change the weight for all incoming routes, use the “weight” option with the neighbor command after forming the BGP peer relationships.

R2(config)#router bgp 100

R2(config-router)#neighbor 100.1.1.1 remote-as 10

R2(config-router)#neighbor 100.1.1.1 weight 200

Learning all of the BGP attributes, as well as when to use them, can seem an overwhelming task when you first start studying for your BSCI and CCNP exams. Break this task down into small parts, learn one attribute at a time, and soon you’ll have the BGP attributes mastered.