Eric Stewart: Running Off At The Mouth

Work finally got me a licensed version of CML. There’s a free version out there that limits you to five Cisco devices, but a basic licensed version will get you 20 devices (last I checked, $199 or 2 CLCs). Per the benefits of having an admin of a vSphere environment that likes/fears me, I didn’t have to worry too much about finding hardware or deciding on exactly what method I was going to use to run the thing.  I will say that we did have to go through the process three times, as first there were disk limitations we needed expanded, then some customization (that we got wrong so we had to do it again).  The only other note is that we ended up having to expand the RAM and CPU so that it could handle a decently sized lab (one of the many I am or have put together is one for my juniors working on CCNA, and it’s running CSR1000v routers along with a few switches and a lot of Etherchannel).

I’ve been looking for something like this for a long time.  Way back when I had larger inspirations, I had a cobbled together ESXi based lab running 20 CSR1000v routers (which would have issues starting all 20 at the same time).  That kind of fell by the wayside as I gave up on the CCIE and was designed after a recommended layout from a training company.  But now that I’m working on getting the CCNP back fully certified, I’m really having way too much fun doing reading on ENARSI exam topics and throwing together labs that might be lacking from the Boson NetSim that I’ve been supplementing my studies with.  NetSim is great, don’t get me wrong – it provides a guided environment for learning key concepts – but sometimes it lacks something I want to cover, or sometimes I just want to build a basic lab from the ground up and look at a concept myself.

For example, here’s a YAML file you should be import into your own CML. It contains five routers connected together, each with a Loopback and a /24 network (and also some v6 addressing) that you can throw EIGRP on (not configured – up to you to do it via either named mode or classic).  Also, every inter-router link has a custom delay of 10 set.  Set variance to 2, then change a delay or 2 from 10 to 9, and see what happens in your route tables.

The other feature I dearly love in CML that is rare to get somewhere else is the built in terminal server.  You don’t have to plod through using the web based consoles – you can just ssh into your CML install with the lab running, run a command, and there you are on the console.  It’s incredibly useful if, like me, you’re used to running multiple terminal windows (Terminator for me on Linux and even Windows Subsystem for Linux, or iTerm2 for Mac) and like to be able to see what’s going on on multiple routers or switches (super handy for debugging across multiple devices).  I can even set up aliases to run an ssh command to pop me directly into a device:

ssh -t <my.cml.ip.address> "open /LAB/DEVICE/0"

and there I am.  The disconnect function (CTRL-] for those who forgot how to get out of a telnet session – and yes, I know it’s not telnet, but it was the one thing I tried that prevented me from having to go to the Internet to ask it how I drop a terminal session) will cause the connection to drop all the way out rather than just back to the terminal server.

There are benefits to laying out the IP addressing yourself using your preferred schema, putting the connections together yourself, building your basic config, and firing the lab up.  You have to go through the process of fixing your mistakes and maybe redoing your base configs.  You’re more familiar with the lab and can focus on learning concepts rather than learning the layout.  In the end, that time spent might just equal out and I’m finding it useful to go through both the Boson NetSim labs as well as making my own … but I will say, I find it just a bit more rewarding when I learn something on a lab I built myself in CML.

Of course it is also an additional expense (if you want more than five Cisco devices, or need to find a machine powerful enough to run what you want to run), and getting the materials together to seriously take on the CCNA or CCNP exams can be more costly than someone might want to invest.  But if you can get work to pay for it, a training company like Boson can provide learning materials (labs, exam sims, and a structured course) or instruction.  But if you need something more, CML might just be the thing that scratches that itch.

One more recommendation: Wendell Odom is producing a lot of valuable materials for the CCNA student over on his YouTube channel, and even has a series about CML.  If you’re working on your CCNA or thinking about it, check his stuff out; dude literally wrote the book on the CCNA.