CCNA Difficulties 5: How to Approach Sims

What's the best game plan for Sim questions?

You know they're coming, but then it happens - you click for the next question, and it's one of the dreaded Sims. Do you break into a cold sweat? Freeze? Rush? Or do you approach these questions with confidence, ready to find the problem, fix it, and claim all the points, and be rewarded for how well you prepared?  This week, I'll ramble a bit about how to prepare and approach questions

First, a quick review of  few interesting points. More than half of us surveyed on the last post have no time management strategy to speak of going into the CCNA exams. Wow. I figured that a low percentage of us would be as picky as me with time management, but given the fact that time pressure seems to be a common issue, the percentage without a particular plan surprised me. For those of you who've not read the earlier posts in this series, take a few moments to look at our survey of exam-day CCNA issues - the Sim and Simlets were chosen about 15% (each) of the time as the biggest reasons why the exams may be difficult. I'll look at Sims today, and maybe give a few words on Simlets before I'm done.

So, I sat at Panera's today, sipping my coffee, and contemplating this whole topic. (That's my reward for doing the blog - a coffee at Penera's, instead of sitting in dungeon - I mean office - another morning.) Anyway, I think there's probably three approaches that one could take towards a Sim question, whether intentional or by accident. (If you use another, tell me...)

See the problem and react: With this approach, you read the problem, and whatever pops to mind, you go look. A can't ping B? Go to the router nearest A, and do your top 3-4 shows. Ping B from that closest-to-A router. Do a quick show run. Whatever comes to mind, relying on your experience and intuition to find the answer quickly.

Structured troubleshooting: While no one troubleshooting methodology works for all people, you can take a structured approach to troubleshooting. (I've even got some material dedicated to just that in my books, in part because it's inside the scope of CCNA as an end to itself.) Following such a plan can lead to identifying the root cause. Compared to "see problem and react", you probably find the answer in a more consistent amount of time, whereas "see and react" may find the problem quickly.

Show run to the max: The answer to a Sim problem is to change the config. So, doing an inspection of a show run on all the Cisco devices in a Sim may reveal the problem quickly, particularly if you have mastered the configuration steps.

I've pondered this many times, including today at the coffee shop: if your only goal is to get Sim's right on the exam, what's the best approach? I have often concluded that doing show run, particularly for CCNA, will get you to the answer fastest. If it gives you heartburn to rely just on show run, and nothing else, you can always do a few other show commands to confirm what you find in the show run commands. EG, if you find that the RIP config does not have a network command that matches interface F0/0, you can then confirm it with a show ip protocols, confirm it by going to the other router connected to that same LAN and see that it learned no RIP routes, etc.

However, you can't just show up on exam day and decide that since Wendell said that the "show run to the max" strategy would work best that you should do exactly that. You need to do a little bit of preparation. And maybe we would need a some more obvious practice tools as well. To be ready for the "show run" strategy, I think you'd need to do the following:

  • Understand all the config commands
  • Practice them
  • Build your own checklist of CCNA-level config commands, in the order that you'd see them in show run, and practice analyzing sh run in any lab, book, video, etc where you see an example

The first two tasks are somewhat obvious. Read my books, or someone else's, and make sure you get it. Practice on your favorite hardware, Sim, or Emulator. (See many past posts this year for discussions on that front. But this 3rd item I think can be the difference between being a good "see problem and react" person and someone who can look at "show run" and quickly find the problem.

Of course, I want to know what everybody out there uses. Here's a poll. Then flip over to the next page, and I'll look at this config checklist tool in a little more detail.

What I'm suggesting here is that once you've finished studying all the core material, you build a checklist of configuration. You organize it based on what you'd see in show run - ie, interfaces, then routing protocols, then ACLs, then console/VTY lines. And then when you do any of your hands on work, also do a show run, and ask yourself, "what's missing? What's wrong?", relying on your checklist. The simple process of creating such a list of your own, and making yourself think about it, could give you those extra skills to find the answers to Sims very quickly.

For example, here's a sample such list. This list would be useful to apply to any Sim question that boils down to "A should be able to ping B, but can't. Fix it." At least it would work well if the config issue is on a router, and not on a switch. When doing a "show run" on a switch, look for these:

1)      LAN Interfaces:

1.      "shutdown" configured?

2.      " ip address" configured? Does subnet number match the hosts on the LAN?

3.      "ip address secondary" configured? Is it not configured, but needed?

4.      Ip access-group configured? If so, check to see if ACL is correct relative to the question.

5.      If trunking is configured/intended, confirm VLAN (encapsulation dot1q vlan-id) matches

2)      WAN Interfaces:

1.      "shutdown" configured?

2.      "clock rate" configured? (Use show controllers to confirm.)

3.      " ip address" configured? Does subnet match other router?

4.      "encapsulation type" match on both routers? (ppp or hdlc) (ignoring Frame Relay in this list)

5.      If PPP, look for "ppp authentication", and if so on either side, check CHAP configuration

6.      "Ip access-group" configured? If so, check to see if ACL is correct relative to the question.

3)      Routing Protocol

1.      If VLSM is used: RIP: is "version 2" configured on all routers?

2.      If >1 classful network, is "no auto-summary" defaulted/configured? What routes result based on whether auto-summary is on or off?

3.      Do the "network" commands match the required interfaces?

4.      Are any "passive-interface" commands configured, and if so, does that cause the problem?

A list this long would be somewhat useless as a beginning point for study, but late in your study, such a list, particularly a list you build, should start triggering your memory. The idea would be to get to the point where you look at a config and know what's extra, and what's missing, and then solve the problem quickly.

So, let's try it out. Let's say R1 and R2 both have F0/0 and S0/0 interfaces, and they connect with a serial link. R1's config is below. If you can predict the required configuration on R2, you should also be able to be ready for finding missing or extra config on R2 on the exam. So, let's say that the Sim starts with the following config on R1, and the requirement is that R1 be able to ping host B, IP address, which is on the LAN connected to R2. You can work out your config on your own, and I'll do a quick post about this problem next week sometime.


int f0/0

 ip addr

 no shutdown

int s0/0

 ip addr

 clock rate 1536000

 encapsulation ppp

 no shutdown

router rip


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