Configuration Policy and Operational Data

Terry Slattery
Principal Architect

I’ve written before in Subsystem Configuration Policy Check about incorporating operational data with configurations for performing configuration compliance validation.  Another example, with a different twist to it, occurred last week while creating an NTP policy check on a customer’s network.  The NTP design is three layers.  There are two stratum 1 clocks, one per data center.  Within each data center is a core 6500 that uses the master clock within the data center as its clock source.  There is a large set of distribution layer devices that reference the core 6500s as ntp servers using the following configuration:

ntp server  ! Datacenter 1 6500
ntp server  ! Datacenter 2 6500

Validating the configurations of the distribution layer devices is pretty easy.  Create a device group of all core and distribution devices, exclude the two core 6500s, and check that the configurations include the above commands.  It is good practice to make sure that there are no other NTP configuration statements in the configs.

The catch comes with the edge devices.  The network is running MPLS and the CE devices may not have a route to the core 6500s.  So the CE devices are configured to use their neighboring PE devices (the distribution layer), as their clock source.  The IP address in the NTP configuration statement depends on the address of the neighbor.  The configuration policy validation system needs to run some commands on the CE device to determine the PE’s address (e.g., show cdp neigh detail), then check the configuration for the NTP statement that uses that address.  This is a simple case of configuration compliance; I envision some configuration checks that might need the output and merger of multiple commands in order to determine the required configuration statements.

The important concept with this example is that configuration policy checking isn’t just about looking for a few commands in the configuration.  The policy compliance system needs the ability to incorporate operational and as-built data into its compliance checks.



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


Leave a Reply


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.