Joining the Cisco Team

HeadShots-10pToday was a bittersweet day for me. It was my final day working with a great group of people at a prominent community bank. I have nothing but good things to say about the people, the organization, and the interesting projects I’ve been involved in. I’ll miss everyone a lot and plan to stay in touch.

Tomorrow I begin a new role as a Systems Engineer at Cisco Systems. I will be working with the SLED (public sector) sales team in Kentucky and West Virginia. In this role I hope to broaden my knowledge of networking components and spend time helping customers better position their technology infrastructures.

What this means for me–

I will be aggressively learning the Cisco Product lines, including areas that I previously had less exposure to. I will take advantage of the resources I have and marry my vision of the changing network industry to the components Cisco positions into higher education environments. My intentions include better understanding the roadmap and technical details as they pertain to the integration path from traditional networking to software defined approaches.

But what about…

As long time PacketU readers know, I have written positive and negative articles about many vendors. All vendors have their strengths and weaknesses. We regularly see them demonstrate both extremes at events like GestaltIT’s Networking Field Day. Given the fact that I am no longer in a neutral position, future articles will be less about vendors and my opinion on their specific implementations.

I do recognize that no vendor is the best at everything. My belief is that the best solutions are based on good technology that is properly implemented and supported. Cisco has a broad range of good technology and it is my job to see that they are properly implemented and integrated into the ecosystems in which they are installed.

What Does This Mean For PacketU–

The original intent with PacketU was to create a place to learn about networking. This was to include protocols, concepts, configurations and processes. I hope to circle back and accelerate those goals. My belief is that my own opportunity to learn will spawn new areas of interest that I will share on this site. I will continue to publish interesting configurations and scenarios as possible. But my goal is to return to a more regular posting schedule and focus more on the modular building blocks that make up what our industry does.


To all of my friends in the industry, all I can say is that you are the best. I’ve met many of you through events like Cisco Live and Networking Field Day. Others have become more than casual acquaintances through social networks like Twitter. I’ll still be around and in touch with everyone. To the PacketU readers, this isn’t goodbye. This is a new chapter in the chaotic [perhaps disorganized] book that my career and PacketU has become.

Disclaimer: This article includes the independent thoughts, opinions, commentary or technical detail of Paul Stewart.  This may or may not reflect the position of past, present or future employers. 

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Podcast Spotlight — Software Gone Wild

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Today’s podcast spotlight goes to Software Gone Wild. This is a newer podcast hosted by our friend Ivan Pepelnjak. The topics are focused on the growing pains the networking industry is experiencing and various forms of automation that are attempting to solve them. This includes various aspects of SDN, NFV and how others are using technology to deliver bigger/better/faster solutions.

Recent episodes include Network Automation @ Spotify and The F-Script with my good friend John Herbert.


Disclaimer: I have no affiliation with the Software Gone Wild podcast or any organization linked to,  represented in or derived from content found in this article. This article represents my own opinions and may not be that of my employer.


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Recognizing IP MTU Issues

At some point, Network engineers will likely face some type of issue with MTU or maximum transmittable unit. Their first experience with this may be an eye opening and time consuming effort. After resolving the issue, those with a thirst for knowledge will take the necessary time to understand the issue.

MTU problems are most often seen when Path MTU Discovery, or PMTUD, fails to function. This is the process by which one end host determines the largest possible packet size to another station on the network. Symptoms of this type of issue include two devices having proven reachability, but applications fail to work in a way that indicates a network issue. Some applications may even crash or hang the system.

Symptoms of PMTUD Failure

  • Hosts may be able to ping one another
  • Service/Port may prove accessible using telnet
  • Severe and persistent application issues
  • Partial page loads
  • Either host appearing to hang

Continue reading

Posted in Network, Technology | 2 Comments

Explanation: TunnelX temporarily disabled due to recursive routing

I wanted to take a few minutes to share a scenario that some seem to struggle with. This scenario is a routing issue that sometimes occurs when an interior routing protocol allows routes to leak back through a tunnel. To demonstrate this, I’ve built a lab with three routers. R1 and R3 are participating in EIGRP and have a GRE tunnel configured directly between them.




Router Configurations

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IP Subnetting Part 3: Understanding the Binary

I’ve often stated how simple subnetting really is. While each individual concept is rather simple, it is the combination that make the holistic process challenging. If we, as humans, could look at the process more like computers and network devices, subnetting would be a much simpler process. In short, some knowledge of binary is an important requirement prior to sharing more complex subnetting examples.

This article will demonstrate the process of converting binary to and from the more familiar decimal numbering system. This will establish the necessary baseline knowledge required to understand when applying subnet masks to IP addresses. The first question we need to answer is–

What is Binary?

Binary, also known as base-2, is a numbering system in which each position only has two possible values. We often represent one possible value as zero and the other possible value as one. Alternatively, it could be represented many other ways including: positive and negative voltage, black and white colors, voltage and no voltage present, or null and not null. This simplicity in representation is what makes the system so advantageous for a computer’s limited discreet capabilities. Continue reading

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Using Cisco’s DevNet “All-in-One VM” as a Free Router Lab

I know many have been [not so patiently] waiting for the arrival of a Cisco virtual lab. Although I haven’t heard any official release date for VIRL or CML, there is a small scale virtual router lab available today. This lab is the All-in-One Virtual Machine made available on the Cisco DevNet site.

While not a comprehensive lab, it is a quick and easy way to get some real command line experience or test smaller layer 3 challenges. This VM includes 3 routers with a total of 10 routed interfaces in use. There is no access to layer 2, so the topology can only be manipulated by shutting down interfaces on the routers.


Using the DevNet All-in-One Virtual Machine

Continue reading

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Asking for Clarity

Confusion ThumbI have a lot of discussions with vendors, peers and other friends in the business. One of the things that I find challenging is the nuances with the language of technology. Our conversations include things like traffic flow, NAT, SDN, Cloud and many of the other industry buzzwords. Our use of terminology often has different meanings to different people (and in different contexts).

While I don’t fully subscribe to the, There is no bad question philosophy, I believe questions should be asked liberally. The only questions I hate to hear are from those trying to prove their [superior] knowledge. Beyond that, individual research can help with the learning process. However, everyone should have the confidence to ask those questions necessary to grasp the conversation at hand. More than likely others will benefit from the clarification as well.

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Community Spotlight —

Community SpotlightI’ve been reading articles by Jeremy Stretch for several years now. His site,, may be best know for the useful cheat sheets that cover everything from IGP routing protocols to Wireshark Display filters. This site doesn’t end with cheat sheets. It also has many useful articles about all things networking. So if you’re looking for a site to add to you feedreader, check it out.


Disclaimer–I continually get requests for a list of the blogs, podcasts and people I follow to “keep up” in this industry. As a result, I decided to start publishing some of the blogs I regularly read. Links to other content from PacketU or affiliated social channels should not be thought of as a universal endorsement or indication of independence or neutrality for a given external site. Readers should assess ALL applicable content before proceeding with actions that could adversely affect their environment.

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IP Subnetting Part 2: Simple Subnetting Examples

Subnetting is a foundational concept in IP networking. Although it is often misunderstood and even dreaded, this is a simple concept if we could look at things from the perspective of binary. However the combination of binary concepts, IP addressing and subnet masking is a lot to attempt to understand at once.

In this article, we will look at some simple examples that are meant to illustrate the process of IPv4 subnetting. This is not meant to be a comprehensive study. It is meant to build my previous subnetting article and should introduce only basic concepts. In future articles, we will delve into more complex and complete examples of IP subnetting.

In an earlier article, I outlined the concept of Classful IP Addressing. That knowledge is a fundamental starting point for the IP Subnetting discussed here. In that article, I outlined three classes of unicast IP addresses. The class an IP address belongs to determines what part of the address is the network and what part is the host. That assumption can be overridden when by applying a subnet mask to the configuration of a modern IP stack. Continue reading

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IP Subnetting Part 1: What is a Subnet?

We cover all sorts of different topics on this site. Today, we are starting a multipart series on subnetting. These concepts are fundamental building blocks for network administrators, engineers and architects. The subnetting topics outlined in this series should be well understood prior to moving into advanced design or configuration topics. Moreover, the underlying technical concepts of this subject should be understood prior to utilizing any shortcuts to calculate subnet addresses and useable address space.

So the question I ask today is–

What is a Subnet?

If I asked this as a multiple choice question, which one of the possible answers would you choose?

  1. In OSI terms, the layer under the network layer–also known as the data link layer.
  2. A subset of a Classful Network

Continue reading

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Cisco IOS – Understanding IGP Network Statements

One of the things that I find both counterintuitive and often misunderstood is the role of the network command in interior gateway protocols. This command is used in the router configuration mode on Cisco devices. While there are some protocol specifics that should be understood, it behaves similarly between RIP, EIGRP and OSPF. The common misconception is that the network statement determines what will be advertised. While it can affect what is being advertised, that is not the direct purpose of this command.

If you have mistakenly thought the network command determines what is being advertised, you’re certainly not alone. We can even find verbiage in the output of “show ip protocols” that lends credibility to this position. Let’s take a look at the following configuration.


In the above example, I have enable EIGRP on all of the interfaces. Continue reading

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Book Recommendations — Jeff Aiken Series by Mark Russinovich

BookSmallLast week, I spent a the majority of my commute time listening to a cybercrime novel by Mark Russinovich. This book, Trojan Horse, is the second of three books in the Jeff Aiken Novel series and didn’t disappoint in any way. In the past I read the electronic version of the first book, Zero Day. Whether or not you work in information security, you’ll likely find these books enjoyable. Having some grasp of the reach and dependance on information systems, I find these books are reasonably plausible. I plan to listen to the final installment in the series during my travels this week.


Disclaimer: I have nothing to disclaim about this article. The links shared are not affiliate links and PacketU receives no compensation from Mark Russinovich or the vendors distributing his work.

Posted in Rant, Technology | 3 Comments