Interview Questions and CCNA Self-Assessment

You’ve studied hard, and you’re ready to take the CCNA exam. But before you can take it, you get a surprise shot at a job interview. In the technical part of the interview, they see your resume’, experience, and you tell them that you’re ready to pass CCNA. As a result, you may spend the next hour performing what’s essentially a verbal version of the CCNA exam. You pass the technical interview, but as you leave, you also realize that you just confirmed that you’re ready to pass CCNA.

Way back in my Cisco days, I got to be one of SEs that conducted technical interviews for potential new SEs. I found the process very interesting. SEs need technical skills, and the ability to converse and present about those skills. In part of the interview, I’d draw a small network on the board, and toss out some questions, like this:

• If I were your new customer, and you saw this diagram on the board, what would you ask me about this network?
• Design an IP subnetting scheme for this network, and describe tradeoffs.
• PC A pings PC B. What’s got to happen before that ping can succeed?

This was back in the 1999-2001 days, and we’d get folks with CCNA on their resume’, and not CCNP, and they’d be legitimate candidates for the job, at least on paper. Amazingly, some folks could barely answer these questions, and couldn’t get past a cursory description of what happens. Some had clearly mastered the whole question of how does a simple network really work, and why. And oddly enough, there were very few tweeners.

(As a side question – what’s your favorite type or slant on a technical interview question?)

This whole interview thing came up in conversation last week, and later that same day, the topic of CCNA self-assessment came up. What I mean by that is: how do you know that you’re ready to take the CCNA exam? It seems that a lot of people gauge that by their scores on various practice exams. Ick. I’ve written a lot of practice questions that end up in the backs of books, and I have to tell you, it’s practically impossible to write a test that mimics any Cisco exam in terms of scoring. Cisco doesn’t publish how they even calculate the scores on the real exam, and that’s just one of many considerations. (I could spend post just on this, but trying to stay focused here…) But it is a challenge: how do you know you’re ready for CCNA, or any other test?

So, let me pull this together. I’m working on a hypothesis (not even theory yet) that I’ll call the interview self-assessment hypothesis. The idea is this: if you could pass the technical interview of the imaginary network engineer in the opening paragraph – assuming that the interviewer is keeping within the bounds of CCNA – then you’re ready for the CCNA exam.

That’s pretty broad; so let me dive in a little deeper. In one slant, the interviewer supplies:

1. A network diagram
2. Some config

Then, the interviewer asks:

1. Tell me every overhead protocol that occurs that matters to PC1’s pinging PC2.
2. Tell me every overhead protocol that doesn’t matter to the ping.
3. Describe the table entries collected on all devices by the end of this process (e.g., routing table on each router)
4. Describe the sequence of events that occur before the ping works (e.g., switch A places port fa0/1 in forwarding state because…)

As you can imagine, the interview could start more generally, and dive into detail. I used to do that all the time when interviewing folks – they give a solid answer, you dive deeper; they give a weak answer, you figure they might not know the next deeper level on that topic.  

As a self-assessment tool, I’m wondering if the same questions could be posed to a candidate, with some questions. You could write the answers, or even present them to a fake audience in front of a marker board. But just like you might experience in a real interview, you know mid-sentence when you’re really kinda fuzzy on some concept, some interaction, some config, some something. The interview context just brings that self-realization to the forefront, which lets you then go review, read more, practice that topic, etc etc etc.

So, what do you think? Useful? Bunch of hooey? Impractical? Well, if you think there’s any benefit to it, you can try the sample that’s linked here.

Here’s the background on the exercise. Initially, the network works so that PC1 can browse to PC2 at PC2.certskills.com. Then, someone shutdown all the switch and router interfaces. Later, the network is slowly brought back up in stages, and you must describe what happens at each stage. The links are brought up in this order: 

1. Links 3 & 4 (router-to-router)
2. 10 minutes later, links 2, 5, and 7
3. 10 minutes later, links 1 and 6
4. 10 minutes later, PC1 browses to PC2.certskills.com

Your interview tasks are as follows:

Give a general description of what happens after each step. List the functions that occur, and why, but do not detail each packet or detail. For example, if host A needs to find host B’s MAC address with ARP, state something like “host A ARPs to learn host B’s MAC address, so that A can send an Ethernet frame to B.”

List the specific events in correct sequence (e.g., if ARP must occur before STP in a particular case, list the correct order).

Describe all tables built dynamically by any device as a result of either overhead traffic or by the user browsing to PC2.

Here’s the link to the doc with the topo and the configs. Enjoy, question, comment at will.

* Wendell’s products for the CCNA, CCNP and CCIE * Choosing between Sim, Dynamips, Real Gear * How to build a home lab * Index of series covered in my blog