For the last several years a lot of the talk within network engineering has centered around layer 3 technologies. The subjects of WAN optimization, Quality of Service (QoS), WAN acceleration, and routing have consumed our thoughts and dreams, blog posts and podcasts. However, now more than ever, having a strong understanding of layer 2 networking technologies is critical to being successful in this industry.

To the uninitiated, layer 2 networking probably seems simple and straight forward. Take your PCs and servers, plug them into a switch, and it all just works - right? Well, yeah hoss, that's right, so long as you don't run into spanning tree issues, as long as all of your trunks are configured correctly, and unless after consolidating your data centers and virtualizing your servers you've saturated those 1 Gbps and 10 Gbps connections that you thought were overkill when you put them in.

Unfortunately, the best way to learn these technologies is by living through a serious outage or performance issue that was caused by them. Hopefully, you'll never have to learn about Spanning Tree Protocol (STP), VLAN Trunking Protocol (VTP), or dealing with ethernet congestion this way but chances are that if you stay in this industry long enough you will. Between now and then, do what you can start coming up to speed but most importantly, be sure that your management tools make it easy to identify, troubleshoot, and resolve issues of these types. Here are some tips I've picked up over the years to help:

  • Remember that spanning tree is logical and topology based. Keep up to date, detailed diagrams and documention and make sure it's easy to get to
  • Customize your NMS so that your trunk groups are logically grouped together and so that you get events when truck port status changes occur
  • Be sure that your monitoring tools are using 64-bit counters (ifHCinOctets and ifHCoutOctets) and SNMPv2 or v3
  • Don't assume that just because 10 Gbps is a lot of bandwidth that it's enough bandwidth

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