Deploying Datacenter MPLS/VPN on Junos

Tuesday, April 15, 2014 at 1:17 a.m. UTC by stretch

One of my recent projects has been deploying an MPLS/VPN architecture across a pair of smallish datacenters comprised entirely of Juniper gear. While I'm no stranger to MPLS/VPN, I am still a bit green to Junos, so it was a good learning exercise. My previous articles covering MPLS/VPN on Cisco IOS have been fairly popular, so I figured it would be worthwhile to cover a similar implementation in the Juniper world.

For our datacenters, we decided to implement a simple spine and leaf topology with a pair of core routers functioning as IBGP route reflectors and a pair of layer three ToR switches in each server rack. The spine is comprised of four layer three switches which run only MPLS and OSPF; they do not participate in BGP.


This article assume some basic familiarity with MPLS/VPN, so if you're new to the game, consider reading through these previous articles for some background before continuing:

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The Value of a Microsecond

Wednesday, April 2, 2014 at 12:36 a.m. UTC by stretch

While perusing vendor datasheets, have you ever questioned the inclusion of seemingly insignificant latency specifications? Take a look at Arista's line-up, for instance. Their 7500 series chassis lists a port-to-port latency of up to 13 microseconds (that's thirteen thousandths of a millisecond) whereas their "ultra-low latency" 7150 series switches provide sub-microsecond latency.


But who cares? Both values can be roughly translated as "zero" for us wetware-powered humans. (For reference, 8,333 microseconds pass in the time it takes your shiny new 120 Hz HDTV to complete one screen refresh.) So, does anyone really care about such obscenely low latency?

For a certain few organizations involved in high-frequency stock trading, those shaved microseconds can add up to billions of dollars in profit. The New York Times recently published an article titled The Wolf Hunters of Wall Street by Michael Lewis, which reveals how banks have leveraged low network latency to manipulate stock prices in open markets. (Thanks to @priscillaoppy for the tip!)

The increments of time involved were absurdly small: In theory, the fastest travel time, from Katsuyama’s desk in Manhattan to the BATS exchange in Weehawken, N.J., was about two milliseconds, and the slowest, from Katsuyama’s desk to the Nasdaq exchange in Carteret, N.J., was around four milliseconds. In practice, the times could vary much more than that, depending on network traffic, static and glitches in the equipment between any two points. It takes 100 milliseconds to blink quickly — it was hard to believe that a fraction of a blink of an eye could have any real market consequences.
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Learn Python

Thursday, March 27, 2014 at 1:10 a.m. UTC by stretch

Around six years ago, I decided to start a website called Maybe you've heard of it. Most people turn to a purpose-built content management system like Wordpress or Drupal for such an endeavor, but I needed greater flexibility to achieve some of the projects I had in mind. This meant I needed to learn a programming language and write a good amount of the site's logic myself.

I already had some experience dabbling in PHP, but wasn't thrilled with it. I figured if I was going to learn a new language, it should be useful as a general purpose language and not just for building a web site. After a bit of research and deliberation, I chose Python (and the Django web framework).

The purpose of this post is to convince networkers with little to no experience writing code to learn Python. In the past I've encouraged fellow networkers to pick up any programming language, as it's more important to think like a programmer than it is to gain proficiency in a particular language. However, I've realized that many people get stuck on which language they want to learn, lose motivation, and end up not growing proficient in anything. So, I've started telling people to skip that first step and just learn Python.

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Packet Life Turns Six

Sunday, March 23, 2014 at 9:40 p.m. UTC by stretch

Today marks Packet Life's sixth birthday, and I'm celebrating by launching the new site format I talked about in January. The relaunched site is hosted on an entirely new server from Linode, which means you can (finally) access via native IPv6! The entire code base has been rewritten on Django 1.6, and should feel lighter and more responsive. The layout has been rewritten as well using the Bootstrap CSS framework.

You might have noticed that some components of the old site are now gone: The discussion forums and wiki have been axed in favor of focusing more on the site's core content. The tools armory, which was initially in jeopardy, has been maintained in response to community interest (although I do intend to spend a good amount of time cleaning it up).

There are no doubt bits of code here and there that need a tweak or three, but generally speaking the site is up and running. If you do encounter an error, rest assured that I've been alerted and should have it fixed in little time. If you feel that something is terribly amiss, give me a shout on Twitter and I'll look into it ASAP.

I want to thank everyone for their patience during the transition. I'm very excited about finally revamping the site, and paving the way for cool new things!


Selecting Shapes by Layer

Wednesday, February 26, 2014 at 12:20 a.m. UTC by stretch

Selecting shapes and connectors one-by-one in Visio can be tedious, especially when working with large or repetitive drawings. If you've been drawing for a while, you've probably gotten the hang of selecting just the right subset of shapes using the rectangular select tool, and employing the control key to add or remove any outliers as desired. This can be time-consuming though, especially when you want to pick out just a few connectors from a jumble of criss-crossing lines.

Here's a trick to try next time you find yourself excessively control-clicking: Identify each logical group of shapes or connectors that you'll likely want to tweak, and bundle them up into to their own layer. You can then use Visio's "select by layer" option to grab them all at once later. Take the drawing below, for instance.


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Overhauling for 2014

Monday, January 13, 2014 at 2:23 p.m. UTC by stretch

Regular readers no doubt have noticed that I haven't posted anything new in the past few months. I've been pretty busy with the holidays, home projects, and adjusting to a new job, and haven't had much time or motivation to devote to writing. Good news though: I have started on a long-overdue refresh of the Packet Life design and code base.

When I originally debuted Packet Life, I ultimately wanted it to serve as major community hub, so I built in features like the wiki and discussion forum. Although Packet Life has grown quite popular over the last few years, these areas of the site have seen little activity. Acknowledging that there are more active and useful sites out there which serve these functions, I've decided to chop off some of the bloat in favor of focusing on the blog and the site's other more popular features.

Here's the fate I've outlined for each function of the site:

Blog: The blog is the heart of the site and will remain mostly unchanged, albeit refreshed and optimized. I'm considering allow guest posts but haven't committed to the idea.

Lab: No, there are no plans to bring the community lab back online in the immediate future. Sorry. And if it is revived, it will move to (once I get back to work on that site).

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Last Day to Buy a Poster is October 31

Friday, October 18, 2013 at 3:05 p.m. UTC by stretch

I've been selling physical copies of my 36x24" IOS Interior Routing Protocols poster for a while now. Unfortunately, Google Checkout is going the way of Google Reader next month and soon I will no longer be able to accept payments. Thus, October 31st will be the last day to order copies of the poster.

The PDF will of course remain freely available for download if you'd like to print the print poster yourself after the deadline.



VRF Export Maps

Thursday, September 26, 2013 at 10:48 p.m. UTC by stretch

VRFs are an excellent tool for maintaining segregated routing topologies for separate customers or services. I've previously covered inter-VRF routing using route targets, but what if we only want to export a subset of the routes within a VRF? Here's a scenario in which this would be desirable.


Customers A and B each have a site network and a colocation network, and both customers need access to the network in the Services VRF. The customers must utilize unique IP space in order to prevent overlapping networks, so each customer has been allocated dedicated IP space from their common provider out o Unfortunately, customer A is still has some networks within the These networks need to access services in the host colo, but the service provider can't allow this space to be advertised into the Services VRF as it's not approved IP space.

Our goal is to export only the networks within the space from the customer VRFs to the Services VRF. How can we accomplish this?

Let's have a look at the initial network state. (This lab was performed using a single router for simplicity. In the real world, these customers would typically be connected via an MPLS VPN.) Each customer and colo network has its own VRF and dedicated route target (RT). The Services VRF has been configured with an import/export RT pair for scalability reasons. No export among VRFs has yet been configured.

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Announcing Labkeeper

Tuesday, September 3, 2013 at 12:23 a.m. UTC by stretch

It's been nearly a year since I had to take the community lab offline to relocate my home, and I still get frequent emails asking when it will be returned. Sadly, my plan to host it with my current employer didn't pan out, and I'm still searching for a suitable host in the Raleigh-Durham, North Carolina area. (If you might be able to give the lab a good physical home, please let me know!)

I also get a lot of emails asking if I can share the scheduling application I used to make the lab available. In short, no, I can't. Not because I don't want to or because it's secret, but simply because that code was written specifically for the site and is not in the least bit portable. But these requests got me thinking: A lot of people obviously would like to be able to share their labs, they just need a platform. Maybe I could rewrite and improve upon the scheduling application to spin it off as its own service.

If you follow me on Twitter, you may have caught one or two references to a new project recently. Indeed, this is exactly what I've been working on for the past couple months during my precious free time: A centralized authentication and scheduling service people can use to make their own training labs available to friends, coworkers, or the general public. I call it Labkeeper.

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Lessons Learned Writing a Custom Config Builder

Friday, July 26, 2013 at 2:34 p.m. UTC by stretch

A while back, I set about developing a modest configuration templating system for my employer. When I first joined the company, new network devices were being provisioned using configuration templates stored as Microsoft Word files, which, as you can imagine, was pretty painful. Each variable had to be identified and replaced by hand in a tedious and error-prone process. I wanted something better, but also cheap (or free) and simple. So I started building something.

To kick off my crazy project, I first decided to build a web application based on the Django Python framework (the same platform on which runs). Django and similar frameworks handle most of the mundane tasks involved in writing a web application and allow for rapid prototyping. It also includes a built-in administration interface for creating and manipulating data independent of the front-end user interface. I spun up a modest internal VM running...

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