Saturday, January 30, 2016

Configuring RSPAN on Cisco Catalyst Switches

I recently wrote a post on configuring port mirroring (SPAN) on Cisco Catalyst switches.  SPAN (switched port analyzer) allows you to mirror traffic from a source or multiple sources on a switch to a destination interface or interfaces on the same switch.  RSPAN (remote SPAN) takes this a step further and allows you to mirror traffic to an interface on a remote switch or switches.


RSPAN configuration is relatively simple and builds upon existing SPAN functionality and configuration syntax.
  • Create an RSPAN VLAN on the source switch, destination switch, and all switches in the transit path.
  • Take traffic from a specified source on switch A, and mirror it to an RSPAN VLAN.  
  • Then, on switch B, use traffic from this VLAN as the source and mirror it to a physical interface

As shown below, traffic mirrored from the switch on the right to the switch on the left can traverse other switches as long as there is end to end L2 connectivity between them (ie. the RSPAN VLAN exists on all switches).

Basic RSPAN configuration is as follows:

Thursday, January 28, 2016

Configuring Port Mirroring (SPAN) on Cisco Catalyst Switches

So you have a network issue.  Or perhaps you don't, but you need to help find the root cause of a performance issue and conclusively show that it's not network related.  In either case, packet analysis is your friend.

At times, it can be convenient (and effective) to capture directly on an affected server or host.  However, you may not always be able to access the affected device.  Even you can, capturing from the affected device is not always the best option due to TCP segmentation offload, checksum offload, and a number of other factors.  (These are outside of the scope of this post, but Kary over at has a ton of great content on packet analysis including why you shouldn't capture on a host.  See here.)

A network tap is the best solution when absolute precision is required.  However, this can be impractical and is often overkill.  This is where port mirroring comes into play.  Cisco gear provides a number of ways to mirror traffic from a specified source (or sources) and get frames from point A to point B for analysis. 

Saturday, January 16, 2016

CCIE "GAP Analysis"

I am in the beginning stages of CCIE preparation and recently had the opportunity to work on a lab scenario with three senior network architects - all current CCIEs.  I'll spare you the details and just say my performance (and troubleshooting approach) in this particular lab fell far short of what I would have liked.

So why is that?  On a daily basis, I design networks.  I perform network assessments and network remediations.  I scale existing networks.  I troubleshoot persistent network issues, at times down to the packet level.  I do all of this quite well.  I work with junior members of my team and explain various networking technologies.  Yet when my feet were held to the fire in a lab scenario, I faltered.

I've put in a tremendous amount of effort over the past few years to master networking fundamentals, and throughout this process, I have earned a number of relevant certifications.  I have read well over a dozen Cisco Press books front to back, I and took the time to process what I read.  I studied using video training materials from multiple sources (including INE whenever possible - I highly recommend Brian McGahan's content).  I built an extensive lab environment (see here).  I configured the relevant technologies, broke them, and troubleshot them.  I implement the bulk of these technologies in production, many of them on a regular basis.

So, again, why did I fall short in a lab scenario?  In an effort to strengthen my weak points and prepare for my CCIE, I've done a high very high level "gap analysis."

Configuration vs. Troubleshooting

There are many technologies I configure on a regular basis but don't often have to troubleshoot outside of a lab scenario.  And quite frankly, I haven't done many troubleshooting labs in the past year since I earned my CCNP.  My responsibilities shifted more to the design side of things, and troubleshooting why an OSPF adjacency won't form isn't something I often do.  In hindsight, I should have kept the momentum going after earning my CCNP and continued with CCIE prep.  At this point, I'm going to have to circle back to solidify some CCNP level topics.

Understanding vs. Execution

I have a solid understanding of a wide variety of technologies.  I could explain many of them at a low level during a quick trip to the whiteboard.  This is a useful skill to have.  However, this doesn't mean I can configure or troubleshoot these technologies on demand.  When it comes to recalling the relevant configuration, show, or debug commands for some of these technologies, I come up up short and have to use reference material.  Conceptual understanding does not equal the ability to configure or troubleshoot a technology on the fly.

Reliance on References

I have developed a lot of my own work notes and reference materials, some of which are posted on this blog.  When writing new configurations, I tend to rely upon known good configurations and references that I wrote.  I have always seen this as being efficient and scalable; why do the same work twice?  However, I now realize this is also a crutch that is going to hold me back as I prepare for the CCIE.

Spread too thin

I tend to spread myself a bit too thin.  I started writing about this here, and then I decided this topic warrants a blog post of its own:
Habits vs. Goals.

Next steps...

To be successful in my CCIE prep, I need to get back to basics and hit the CLI.  In an effort to stay on track and solidify my own understanding of various technologies, I am going to be writing a series of blog posts that corresponds to the CCIE R&S v5 blueprint.  Stay tuned for more.

Sunday, January 10, 2016

Habits vs. Goals

So it's that time of year again.  People set goals.  People chase goals.  Many ultimately fail.  I recently read an article on habits vs. goals over here, and it got me thinking about goals, habits, and balance in general.

I have big goals, and I want to achieve them all at once.   I tend to spread myself a bit too thin.  For example, in 2014 I set the following goals:
  • Study for and pass CCNP route, switch, and t-shoot
  • Run a marathon
  • Help plan my own wedding (I wasn't tremendously helpful), and get married
  • Go on my honeymoon, and while on my honeymoon, study for the CCNP and train for the marathon.
  • Work enough after-hours to cover the flex time for the wedding/honeymoon
  • Achieve a laundry list of professional goals for a major promotion

Generally just a CCNP, marathon, wedding, or major promotion would be a pretty intimidating goal.  Attempting to achieve all of these in one year was definitely quite the challenge.  I ultimately succeeded, but the road to get there was unstructured.  It was a very hectic year. Last year (2015) was more of the same.

Right now I'm working toward even more time consuming goals:
  • Earn CCIE R&S
  • Finish B.S. Information Technology-Security degree at WGU
  • Learn Python and become proficient using it to manage network devices and manipulate configs
  • Develop greater understanding of TCP/IP and packet analysis
  • Train for another marathon, and begin cycling in preparation for an Ironman
  • Start weight training (again)
  • Blog consistently
  • Achieve a laundry list of other professional goals and certifications

As my goals get larger and larger, holding myself accountable and managing my time becomes even more important.  This is where building solid habits comes into play.  I've seen great results using fitness tracking apps such as Garmin Connect, MyFitnessPal, and Withings.  The datafication and gamification these apps provide helps me stay on track.  Tracking progress over time helps me hold myself accountable.

This year I've decided to take a similar approach and track all of the other goals I'm working toward.  There is no shortage of apps for tracking and forming habits.  I found a useful list here.

I ultimately chose because it is cross-platform and easy to use.  It appears to be full featured, and has a nice pretty UI.  As with all of these apps, you get out what you put in.  However, I'm definitely looking forward to focusing on habits rather than goals.  If you develop the habits, the goals will fall into place.

UPDATE 1/29/16:  While I like the premise and basic functionality, the app leaves a lot to be desired.  There is currently no reporting functionality or any way to view historical data.  It seems like a wasted opportunity to collect data on a daily basis and do absolutely nothing with it.  My ideal app would provide a visual representation of habit consistency, trends, and how habits/goals change over time.