Device and Interface Groups Aid Config Policy

Terry Slattery
Principal Architect

Networks use the same devices in many different roles, so configuration validation based on device type isn’t sufficient. There are some configuration things that can be checked across all the devices of a certain type in your network, such as checking the syslog and NTP configuration, or verifying that all the vtys in Cisco routers and switches have an appropriate ACL applied.  But when it comes to other configuration factors like routing protocols or interface configuration specifics, there are other factors that need to be incorporated into deciding which configuration template to check.

Grouping devices by role makes it possible to create configuration policy validation checks that work across large numbers of devices.   For example, checking all the OSPF backbone router configurations or checking the EIGRP stub router configurations needs to be done on only a subset of the devices in the network.  Similarly, grouping of interfaces by functional role, like whether it is an uplink or an edge port, can allow configuration template comparisons against large numbers of interfaces.

The key to device and interface grouping is having an automated method for doing the grouping.  Sure, you can do it manually, and that’s how a lot of systems force you to do it.  Let’s say your network contains 600 network devices.  Are you going to manually classify each device into the proper groups and maintain those groups over time?  Keep in mind that if a device’s role is modified (e.g., it now does QoS classification and marking), you’ll need to add it to the QoS group.  A device can be a member of multiple groups, so adding a new device may mean identifying which groups to which it should belong and editing those group lists.  Manual processes like this are why network management systems turn into shelfware – the process is too intensive to be followed consistently.

If manual processes don’t work, what will?  A rich grouping language must be used to classify devices and interfaces into different groups.  A device that has OSPF, QoS, BGP, and is a core device may need to be a member of four groups. The device configuration, addressing, and neighbors, may need to be examined in order to classify the device. Interface classification follows similar rules in that its addressing, neighbors, or trunking may determine whether it is an edge interface or an infrastructure interconnection interface. Should the interface be configured with portfast and bpdu-guard?  Should it be set to ‘duplex auto’, or fixed duplex, and what factors determine the setting?

Once the device and interface grouping exists, the configuration policy checking system needs the ability to apply group-specific configuration template analysis. Of course, your network needs to be designed in a way that results in a minimal number of overall configurations or the number of groups and templates will explode and become unmanagable.

Let me know what you’ve found that works well in your environment for configuration validation and how it handles differences in device and interface roles.



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.