What the *, traceroute?

If you've ever done a traceroute from one IOS box to another, you've undoubtedly seen output like this:

R8# traceroute 192.168.100.7
Tracing the route to 192.168.100.7
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.0.1 4 msec 3 msec 4 msec
  2 192.168.100.7 4 msec *  0 msec

That msec * msec output. Why is the middle packet always lost?? And why only on the last hop??

IPv4 QoS Markings Calculator

This is a quick calculator I came up that I could use in the CCIE lab to translate between various IPv4 header QoS markings. As long as I could remember how to draw out the calculator, all I had to do was some basic math and I could translate between markings quite easily.

This post does not explain what the header fields are, why there’s so many or what the significance of one QoS value is over another. I’m making an assumption that the reader is already familiar with QoS concepts.

Here’s the calculator:

Each column represents one bit from the Type of Service (ToS) field in the IPv4 header. The right-most column describes what each row is for. The very last row is meant to be filled in by us; it’s the input into the calculator.

As an example, let’s say we Continue reading

IPv4 QoS Markings Calculator

This is a quick calculator I came up that I could use in the CCIE lab to translate between various IPv4 header QoS markings. As long as I could remember how to draw out the calculator, all I had to do was some basic math and I could translate between markings quite easily.

CCIE R&S – By the Numbers

When I started studying in earnest for my CCIE, I started a log of how I was spending my time studying, which books and papers I’d read, videos I’d watched, and so on. I thought it would be a neat exercise to look back afterwards at what it took to achieve this goal. I’m also somewhat self-deprecating and tend to minimize my accomplishments, so having this data is a way for me to remember that this wasn’t a small accomplishment at all.

1,041,248 bytes of digital notes taken

13,916 km traveled (8,711 mi)

1,432 total study hours

652 hours in the lab

321 hours of just reading

223 videos watched

161 hours spent watching those videos

128 PDF documents read

23 books read

5 figures worth of expenses and costs

1 completely trashed USB mouse

Beyond these numbers there’s the intangibles that went into this goal too. No vacations. Giving up free time on evenings and weekends. Not seeing friends as much. Not spending as much time with family. Maintaining focus constantly on the end goal. Constantly staying up late and getting up early.

Looking back at all of this, I realize that becoming CCIE certified isn’t just about Continue reading

CCIE R&S — By the Numbers

When I started studying in earnest for my CCIE, I started a log of how I was spending my time studying, which books and papers I'd read, videos I'd watched, and so on. I thought it would be a neat exercise to look back afterwards at what it took to achieve this goal. I'm also somewhat self-deprecating and tend to minimize my accomplishments, so having this data is a way for me to remember that this wasn't a small accomplishment at all.

Hello, I’m 47321

And now the big reveal. The reason I haven’t been blogging or doing much of anything for some time now is because I’ve had a teeny tiny side project going on:

And this week I passed the lab exam! I am CCIE 47321 (Routing and Switching).

Hello, I’m 47321

2014 End of Year Blog Statistics

Although I wasn’t actively blogging this year, I’ve still been tracking views on the site and keeping an eye on number of visitors. I am looking forward to blogging again in 2015 so I wanted to collect the 2014 viewership statistics so I had something to compare to at the end of 2015.

Despite the lack of new content, I’m pretty happy that people are reading the existing articles and continue to post comments and email me questions. Please keep them coming!

Here are the year-over-year statistics for Jan 1 2014 – Dec 30 2014.

Overall YoY comparison:

Once again these stats are courtesy of Google Analytics. If you compare this chart to the 2013 equivalent, you’ll see that Google has changed some of the metric names. Visits are now called Sessions and Unique Visitors are now Users. And like last year’s chart, the first number in gray is the current year’s number, the second number the previous year.

While the number of Users and Sessions grew at a slower rate than in 2013, they still grew! Very cool.

As was the case in 2013, the users visiting the site are primarily made up of brand new visitors. It Continue reading

2014 End of Year Blog Statistics

Although I wasn't actively blogging this year, I've still been tracking views on the site and keeping an eye on number of visitors. I am looking forward to blogging again in 2015 so I wanted to collect the 2014 viewership statistics so I had something to compare to at the end of 2015.

Despite the lack of new content, I'm pretty happy that people are reading the existing articles and continue to post comments and email me questions. Please keep them coming!

Will I Be Blogging Again?

Dan wrote in with a question:

Hey, I like your site as well… are you going to be doing any more posts? It just seems odd that your last blog post was the analyzation of the site and how it portends to your future work. anyway, good luck

I know it’s tacky to write a blog post about how you’re not writing enough blog posts… but here goes.

Yes, I will be blogging again. And I have lots of content ideas. And I’m actually itching to get back to writing. I’ve been working on something else for the past few months and I decided I couldn’t take that on and blog at the same time. So for now my writing is on hold, however I do see and respond to all comments in the articles and am reachable via email as well.

Thanks to everyone who reads and posts comments. I look forward to writing more posts in the new year!

Will I Be Blogging Again?

2013 End of Year Blog Statistics

I debated whether to write an article like this. It seems to be the “in vogue” thing to do if you’re a blog author but I wasn’t inclined to do it until I started looking at the data (I heart data). When I started looking at the data, I saw not only number of visitors and so on to the blog, but a breakdown of browser versions and operating systems (thank you Google Analytics for the rich reports). As is often the case, your data set can tell you more than you initially bargained on.

All of the reports below are comparing year-over-year stats: Jan 1 2012 – Dec 29 2012 vs Jan 1 2013 – Dec 29 2013.

First, the overall picture of visits to the blog:

38% more overall visitors and 53% more unique visitors in 2013. Pretty cool! And over 58 thousand people put eyes on my blog in the past year. That’s something I hope to build on in 2014.

The first unexpected data point I saw is that in 2013, the blog saw more new visitors than in 2012. That means the readership is expanding to include new people which is excellent.

Next up Continue reading

2013 End of Year Blog Statistics

I debated whether to write an article like this. It seems to be the “in vogue” thing to do if you're a blog author but I wasn't inclined to do it until I started looking at the data (I heart data). When I started looking at the data, I saw not only number of visitors and so on to the blog, but a breakdown of browser versions and operating systems (thank you Google Analytics for the rich reports). As is often the case, your data set can tell you more than you initially bargained on.

IOS and NX-OS Platform Identifiers

I was preparing a presentation the other day about the high level differences between IOS, IOS-XE and NX-OS and one of the things I included in the presentation was the various platform and branch identifiers that’s used in each OS. It’s just a bit of trivia that I thought would be interesting and might come in handy one day. I’m posting the information I collected below so everyone can reference it.

IOS

For IOS, you can see the platform identifier in the filename and the “show version” output. If we take an example version string, 15.1(2)SG2, and break it down, here’s what each digit in the string signifies:

The branch/platform identifier can also be seen in the IOS filename:

cat4500e-entservicesk9-mz.151-2.SG2.bin

Here’s a summary of the branch identifiers in IOS 15:

• M/T – 800 Series ISR, ISRg2 (1900, 2900, 3900), Connected Grid Router 2000
• S – 7600 Series Router, ME 3600X, ME 3800X
• GC – 5900 Series Embedded Router
• SE – Catalyst 2960, 3560, 3750, IE 3000 Switches
• SG – Catalyst 4500E (Sup 6E and earlier)
• Continue reading

IOS and NX-OS Platform Identifiers

I was preparing a presentation the other day about the high level differences between IOS, IOS-XE and NX-OS and one of the things I included in the presentation was the various platform and branch identifiers that's used in each OS. It's just a bit of trivia that I thought would be interesting and might come in handy one day. I'm posting the information I collected below so everyone can reference it.

Five Functional Facts about VXLAN

It seems appropriate to write a FFF post about Virtual Extensible LAN (VXLAN) now since VXLAN is the new hotness in the data center these days. With VMware’s NSX using VLXAN (among other overlays) as a core part of its overall solution and the recent announcement of Cisco’s Application Centric Infrastructure (ACI) and the accompanying Nexus 9000 switch, both of which leverage VXLAN for delivering a network fabric, it seems inevitable that network engineers will have to use and understand VXLAN in the not too distant future.

As usual, this post is not meant to be an introduction to the technology; I assume you have at least a passing familiarity with VXLAN. Instead, I will jump right into 5 operational/technical/functional aspects of the protocol.

For more information on VXLAN, check out the draft at the IETF.

1 – VXLAN Use Cases

Despite the apparent ubiquity and fervent hype around VXLAN, it’s actually been designed to solve specific problems. It has not been designed to be “everything to everyone”.

The first, and most often cited, use case is for data center operators that require more than ~4000 logical partitions in the network. These 4000 partitions equate to the maximum number of Continue reading

Five Functional Facts about VXLAN

It seems appropriate to write a FFF post about Virtual Extensible LAN (VXLAN) now since VXLAN is the new hotness in the data center these days. With VMware's NSX using VLXAN (among other overlays) as a core part of its overall solution and the recent announcement of Cisco's Application Centric Infrastructure (ACI) and the accompanying Nexus 9000 switch, both of which leverage VXLAN for delivering a network fabric, it seems inevitable that network engineers will have to use and understand VXLAN in the not too distant future.

As usual, this post is not meant to be an introduction to the technology; I assume you have at least a passing familiarity with VXLAN. Instead, I will jump right into 5 operational/technical/functional aspects of the protocol.

For more information on VXLAN, check out the draft at the IETF.

Why I Use MediaWiki for Taking Notes

I was prompted to write this when I observed someone the other day who was sitting in the same training as me taking notes in a self-addressed email. No offense to people who do this, but W. T. F. How are you going to keep track of that email among the dozens/hundreds you receive every single day?

I take a lot of notes for research, certification study, and training. I use MediaWiki for almost all of these notes. Here’s why.

What is MediaWiki?

First off, MediaWiki is not a text editor. This may seem strange but after reading this whole article, I hope you’ll understand why that doesn’t matter and in fact, why that makes it more powerful. As the name implies, MediaWiki is actually software for running a wiki. In fact, it’s the same software that runs the most famous wiki, Wikipedia.

MediaWiki runs on UNIX (including OS X) and Windows machines. It’s written in PHP and runs under almost any web server (Apache, lighttpd, nginx, IIS). By its very nature, it’s web-based, which plays nicely into one of the reasons I like using it so much.

Simple Markup Language With Rich Rendering

When I’m taking study notes or Continue reading

Why I Use MediaWiki for Taking Notes

I was prompted to write this when I observed someone the other day who was sitting in the same training as me taking notes in a self-addressed email. No offense to people who do this, but W. T. F. How are you going to keep track of that email among the dozens/hundreds you receive every single day?

I take a lot of notes for research, certification study, and training. I use MediaWiki for almost all of these notes. Here's why.

Five Functional Facts about OTV

Following on from my previous “triple-F” article (Five Functional Facts about FabricPath), I thought I would apply the same concept to the topic of Overlay Transport Virtualization (OTV). This post will not describe much of the foundational concepts of OTV, but will dive right into how it actually functions in practice. A reasonable introduction to OTV can be found in my series on Data Center Interconnects.

So without any more preamble, here are five functional facts about OTV.

#1 – OTV Adds 42 Bytes of Overhead

OTV, being an encapsulation technology, adds additional headers to the encapsulated payload. Without rehashing too much of the basics, OTV extends a Layer 2 domain across a Layer 3 cloud. In order to preserve the Layer 2 semantics on either side of the cloud, OTV scoops up the entire Layer 2 packet on one side, transports it across the cloud in the middle, and puts it on the LAN in the other side. This preserves the entire Ethernet header including the original source/dest MAC, and even the CoS bits and VLAN tag.

So to begin with, we’re putting a (potentially) full-sized Ethernet frame – with headers – inside another Ethernet frame. That Continue reading