The Importance of Good Network Hygiene

Terry Slattery
Principal Architect

Just as good personal hygiene is a prime contributor to personal health, good network hygiene is a major contributor to overall network health.  Pete Welcher introduced me to the concept and I’ve found it referenced in a RIPE draft document titled Network Hygiene Pays Off, which talks about source address filtering.  (I also talked about source address filtering a short time ago: Anti-spoofing filters).  Pete’s way of looking at it is more widely encompassing that just source address filtering.

The principle is simple.  Keep the network clean and it will have fewer problems.  When problems do occur, they will be easier to spot and simpler to fix because there will be fewer negative interactions between network subsystems.  If you don’t keep things clean, interactions between otherwise minor problems can create a larger problem.

What’s an example?  Let’s say that you have a network that contains some duplex mismatches between network gear.  But the links are all low utilization and since no one is complaining, you decided that they don’t need to be fixed.  Some time later, a network link or device dies and traffic shifts and one of the duplex mismatched links is now carrying traffic at 30% of its rated capacity.  The error counts on the interface begin going up.  You now have two problems to troubleshoot and correct: the duplex mismatch on the link carrying the current load and the reason for the other failure that caused the traffic to shift.

Most network managers don’t have time to go looking for network problems that aren’t causing an outage.  But it is important to run a clean network so that you don’t have multiple problems to solve when the big outage strikes.  It is also useful to have a baseline of how the network was performing prior to the big outage so that you know what it used to look like and use that information to help identify where the problem occurred and how to correct it.

I like to start with simple things, like brushing your teeth.  Oh, that’s right, we were talking about networking…  Simple things like finding and fixing duplex mismatches, correcting root bridge placement in spanning trees, setting unused router ports and switch trunk ports to administratively down state (so I know when I see a down router port that it is a problem, even in a redundant network).  I look for HSRP/VRRP/GLBP where there is only one device providing redundancy, native vlan mismatches, weak username/passwords, lack of network device security, and source address filtering.  These are just a few of the things that, when correctly configured, constitute good network hygiene.  A list of 25 of them appear in the poster that I developed at Netcordia, The Top 25 Network Problems and Their Business Impact.
If you look at the list, you’ll see that some of these items require configuration checks (think configuration policy) and others require comparing settings between multiple devices.  How do I go about checking all of these things?  Do I have the luxury of a lot of free time?  No.  I use automated tools.

I’ve been looking at a variety of tools recently and still favor NetMRI because of its automated network discovery and automatic checking of a lot of basic network things.  With its Network Configuration Policy capability, I can write simple rules that can identify configs that don’t match what the network’s intended configuration.  And even better, I get a list of exceptions that need to be addressed – kind of a “no news is good news” view of the network.  When I see something it reports, it is something to investigate.  At one site, it found a routing loop that no one had identified because it reported high numbers of TTL Exceeded messages being sourced by a router.

I’m interested in your list of Network Hygiene items.  Please leave them in a comment so we can all benefit.  Thanks!



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.