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Lab Diagrams

CCIE lab exam has been with us for more than 15 years now. In these 15 years, many strategies and many techniques were developed and established themselves as axioms – things you should do when you are taking the lab exam. One of these things is “redraw the diagrams”. In recent months, things in CCIE R&S have changed in such a that may need to force us to rethink that approach. While the main audience of this post are CCIE R&S candidates, other CCIE students may benefit from these words. What happens in R&S, invevitably comes to other tracks, as well!

Challenge of Complex Diagrams

First off, let’s examine a simple network diagram presented below. Let’s work with the assumption that other relevant information, like IP addressing and routing protocols are drawn on the diagram. They are not on this one, but this is just an illustration of the concept anyway.

Diagram

After 15-20 or so minutes, we may end up having diagram that looks something like this.

Hand Diagram (full)

Other than wasting time and introducing few mistakes (let me know when you spot them!), what would be the benefit of redrawing the entire diagram, when the one provided is pretty good to begin with? If we continue working with our own hand-drawn diagram, introduced errors may cost us deerly in the lab.

Does this mean we shouldn’t draw our own diagrams in the lab, you may ask? The answer, as with so many things in our wonderful CCIE world is – it depends.

Section Diagrams

Redrawing the entire diagram may be pointless and a waste of time. However, when faced with apparently difficult task, or a troubleshooting ticket, drawing a section of the diagram may be of great help. Let’s play along and take a look at few possible questions related to the network from our diagram.

    Ticket 5

  • Fix OSPF on routers R12, R19, R20 and R21 so they are able to ping each other’s Loopback0 interfaces.
  • Do not modify any configuration on router R30.

What I may do at this point, is quickly redraw the relevant section of the diagram to make things a little bit more clear. Let’s take a look at that.

Section 1

Since I’m not allowed to touch R30, I’m not even going to draw it. It’s a cloud – a Frame Relay cloud. R12 looks like a hub, with R19, R20 and R21 as spokes. That tells me pretty much what I need to do there…

Let’s look at a little bit more challenging task next.

    Redistribution

  • RIP is running between R10, R11, R13 and R14.
  • EIGRP is running between R13, R14, R15, R16, R17 and R18.
  • Interfaces connecting only R13 and R14 run EIGRP.
  • Mutually redistribute between all protocols running on R13 and R14.

Again, we can quickly draw a redistribution diagram here that can help us understand what needs to be done. Remember, if you can – use colors. Personally, I have color code for all IGPs. I use red for RIP, green for EIGRP and blue for OSPF. You are, of course, free to use whatever you like! Let’s take a look at the diagram I might make.

Section 2

In this section diagram, I have everything I need. I know which routers are running RIP, which are running EIGRP and more importantly, I see the redistribution points clearly. Tags that will be used for filtering are also there. I indicated cyan and magenta redistribution directions. I have added descriptive rules in upper corners, indicating what needs to be disallowed and allowed in each direction. In bottom corners I included route-map names for both redistribution directions. This is something I always do when I have anything but very straight-forward redistribution scenario!

This may look confusing at first glance, but after you sit in one of our Instructor Led Classes, it may make much more sense!

Conclusions

Unless you have a really bad diagram in front of you, don’t waste time redrawing entire topology, especially if it’s particularly large. Use diagrams you have provided and if they are missing some information or you may need to analyze specific case in depth, create a section diagram and use that one instead. You are much less likely to make mistakes and you can more easily add the relevant information for the task at hand. This can become very useful when you start end-of-day verification process!

Being able to draw quick section diagrams is very important and this blog barely scratches the surface. You should practice this technique as it will probably save you a lot of time and help prevent mistakes in the lab.


Marko Milivojevic – CCIE #18427
Senior Technical Instructor – IPexpert
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