NANOG Posting on Configuration Analysis

Terry Slattery
Principal Architect

The North American Network Operators Group (NANOG) email list just had an interesting exchange about  configuration management.  Someone asked:

For auditing, is there any Cisco Router/Switch configuration analysis tool?

Someone else replied:

Depends on your goal.
Trying to identify and fix configuration problems?
Take a look at NetMRI from Netcordia.
We demo’d it. We liked it and bought it.

There are two types of configuration problems:

  1. Configuration changes that are incorrect.
  2. Configurations that don’t match your configuration policies.

I’ll cover the first of these here and follow up with another post about the second.

Since 40%-60%* of network problems are due to configuration mistakes, checking device configurations is critical to network uptime.  And when you have an outage, the most likely cause is network configuration change.  Obviously, tracking configuration changes can have a big impact on network reliability.  What kind of tracking is useful in real networks?

I like to have a configuration repository where all past configurations are kept.  Keeping the last few copies isn’t sufficient when someone is doing a config debug scenario and will blast through ten or fifteen config changes in an hour. Keep them all; disk space is cheap!  Of course, you need a way to organize them so you can quickly identify which configurations to compare when looking for a change.  Once you’ve identified two configs to compare, use a side-by-side contextual diff display that colors the changes, as shown in the figure below.


How do you prevent the incorrect configuration from being fielded?  Some organizations use a change control board and peer review process to review the configurations before they are fielded.  Configuration control like this is a sign of a more mature organization, provided the process is followed (having a process and not following it has the opposite sign).   If you have known configuration policies for each network building block module, then you should be able to compare your validated configuration templates against the change to determine if there is a deviation from policy that should be flagged and investigated further.



Re-posted with Permission 

NetCraftsmen would like to acknowledge Infoblox for their permission to re-post this article which originally appeared in the Applied Infrastructure blog under


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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


John Cavanaugh

CCIE #1066, CCDE #20070002, CCAr
Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.