Studying for CCDA

I’ve decided to start studying for the CCDA. I haven’t taken any tests for awhile and I’d like to start down the road to renewing my CCNP R&S (which admittedly won’t expire for another 26 months). I plan to knock out the CCDA before November is over and then the CCDP by the end of February 2019.

My normal study patterns are typically loose and I don’t set any deadlines. I am still usually able to achieve goals in this fashion. This time however, I’m setting weekly goals of material to cover and will work every hard to ensure I stay on path. Part of the reason I am doing this is to determine how well I can stick to a schedule, as I might entertain studying for the CCIE R&S after this. I’m not 100% committed to that path though as I learn more about network automation and spend a good chunk of my free time on other skills that I think are useful and valuable.

I may be posting some of my notes on the CCDA going forward. I haven’t seen too many online resources for CCDA, and I hope it helps someone else studying.

This Guy Logged Putty to a Network Share and You Won’t Believe What Happened Next

It turns out that logging putty sessions to a network share is, or can be a bad idea. I learned this after getting a new laptop at a new job. I had several workstations and wanted to log all of my putty sessions to the same folder – I figured this would help with troubleshooting at some point down the line. What I didn’t realize was that this would cripple me for a few days as I worked and tried to figure out why my sessions were so slow.

It didn’t help that I had just bought a sketchy USB-to-serial cable and was questioning the drivers I had installed. Putty sessions would often hang before I could even login to a device. How frustrating! I realized that when I was connected to a wireless network I had the most issues – using a wired connection was typically no trouble at all. At some point in troubleshooting almost any strange issue, I turn to Wireshark. Wireshark can be a great tool when you have a defined problem scope, which I didn’t quite have here – but I was on the verge of something.

I saw a lot of chatty SMB traffic going back and forth between my laptop and a file server. The destination folder matched my putty log folder. Suddenly it hit me – the added latency of a wireless connection combined with the chatty nature of the SMB traffic caused all of the ssh sessions from my laptop to be mostly unusable. So obvious and clear, why hadn’t I thought of it sooner? As soon as I changed the logging path to a local drive, my sessions sped up dramatically.

This is a strange problem that I suspect won’t help anyone specifically – but I do hope it’s at least mildly interesting.

No Safe Changes

Settling into a new job – I was working on what I thought was a routine change. Setup a spare switch in a temporary location with a basic config. Easy enough, right? The time came for me to configure a port on the upstream device. The device in question was a legacy Catalyst 65xx – a big chassis switch that I had read about but never had any experience with. The port I was going to use had a dozen lines of configuration already applied – mostly related to queuing. My first instinct was to issue a ‘default interface <slot/port>’ command and start from scratch. This is almost always the right thing to do, as it ensures no confusing stale configuration remains (I’m looking at you ‘switchport access vlan # / switchport mode trunk’).

Leaning over, I asked my co-worker if the ‘default interface’ command worked on these things. After being assured that it would be fine, I held my breathe and pressed ‘enter’.

I was greeted with several lines of output related to quality of service (QoS) being set to default values on a range of interfaces. Crap! Had I just wiped out the configuration for an entire line card?

No – it turns out the architecture of these switches is such that the queuing must be configured identically on specific groups of ports. I forget if it was all 48 ports on the card, or  16, or whatever, but the point is that I made a simple change and there were unintended consequences. At least Cisco was kind enough to leave me a message about it. And it didn’t bring the network down.

This was a reminder that even the most mundane, routine, everyday changes can go sideways when you least suspect it.

New Opportunities

I have recently gone through some life changes which means I have less time to blog than I’d like. I wanted to publish a new post every week or two, however with the transition I have been busier than usual. The good news is that when I can regularly post again, I should have a lot of new content to share! Sorry for the extended absence – I hope to be back in the swing of things shortly.

When Should You Automate Something?

Automation has been hot in the networking world for quite some time now – however I still see many people asking for advice on how to get started. If you don’t know of a project or something you can do for fun, think some more.

Others ask at what point they should start automating tasks. Some like to break the answer down to a simple equation where if (time to automate task) < (time to complete task manually),  you should clearly automate.

def should_i_automate(time_to_do_manually, time_to_automate):
    if time_to_do_manually > time_to_automate:
        return “You should automate this task!”
        return “You should do this manually!”

This leaves out the intangible benefits of skills learned while automating tasks that can be leveraged in the future. It leaves out the hard-to-quantify human errors that are avoided when humans are removed from repetitive tasks. I don’t know about you, but I find coding to be challenging and rewarding as well. These are just a few reasons why you may automate something even when the time payout isn’t immediate. What are your thoughts?