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Broadcasting news, tips, and troubleshooting on networking technologies.




Cisco Embedded Event Manager (EEM) Config Diff Generator

TACACS+ is the preferred method to log CLI commands at any enable level whether performing show command or making config changes.  See AAA and TACACS commands for more information.  There’s open source software if you don’t have or can’t afford Cisco ACS or similar products that can do TACACS and RADIUS.

But for a really cool and rarely used feature, you could have the switch itself run a config diff(erence) on the running-config and startup-config and email the changes or deltas to you!  Code snippet here.

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Cisco WLC (Wireless LAN Controller) Series - IP & VLAN Planning

In part III of this Cisco WLC Series, we’ll discuss IP and VLAN Planning, an unexceptional area in network design that often doesn’t get the level of treatement it deserves, in the context of wireless. 

Any good IP and VLAN design needs to accomplish three goals.

  1. Able to support current needs
  2. Permits some degree of flexibility 
  3. Creates a framework for security

These goals are no different for wireless.  In the corporate network I support, the IP and VLAN Plan was established many years before wireless was given a serious seat at the table.  Only by meeting the second goal that allows for flexibility, wireless was able to be overlayed with the wired network with enough degrees of separation to continue to meet the third goal of maintaining a security framework.  Some of the decisions that go into a sustainable IP and VLAN Plan don’t require more than a few extra cycles of thought that readily pays for itself in unforseen ways.

To jump to the beginning of this series, see the Introduction.

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Cisco WLC (Wireless LAN Controller) Series - Building Blocks

In this section on the Cisco WLC Series, I’ll attempt to show the relationships between the basic building blocks in a concise and meaningful way.  We’ll cover:

  1. Ports
  2. Interfaces (Service, Management, Dynamic)
  3. Interface Groups
  4. WLANs

To jump to the beginning of this series, see the Introduction.

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Cisco WLC (Wireless LAN Controller) Series - Introduction

After many late nights and pouring over countless sources of documentation, including the voluminous docs found at, all the concepts and design elements that comprise a Cisco WLC (Wireless LAN Controller) architecture have finally “clicked”.  I’ve somehow managed to escape enterprise wireless until now.  Learning a new platform is simultaneously exciting and challenging, particularly on day 1.  For any seasoned network engineer, jumping into the depths of enterprise wireless for the first time presents a steep learning curve that quickly needs straightening out.

Image (c) 2012 - used with permission

Tackling a new GUI/CLI is initially a series of exercises and tests in attaining enlightenment of not only the overarching architecture of the platform, but in understanding subtle nuances and hierarchical relationships.  Sample walk-thrus of configuration rarely explore these nuances in any meaningful way; that takes frequent help-searches and reference materials.  The process of reaching your “light bulb” moment is akin to having a pile of multicolored marbles that you can finally begin to order in a meaningful way.

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Top General Network Errors from Microsoft

3,840 current GOOG for “general network error” on

When in doubt, Microsoft (as does everyone else) throws the network under the bus every time they characterize unknown errors as network errors (generally speaking). A vast majority of hits are SQL-related which can be expected with the number of clients talking to SQL servers over the network compared to other network resources (or should I say resources on the other end of the network).

Here are a few Microsoft KB articles helping to promote confusion and pointing the finger in another direction:

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