Path MTU discovery in practice
Last week, a very small number of our users who are using IP tunnels (primarily tunneling IPv6 over IPv4) were unable to access our services because a networking change broke "path MTU discovery" on our servers. In this article, I'll explain what path MTU discovery is, how we broke it, how we fixed it and the open source code we used.
First there was the fragmentation
When a host on the Internet wants to send some data, it must know how to divide the data into packets. And in particular it needs to know the maximum size of packet. The maximum size of a packet a host can send is called Maximum Transmission Unit: MTU.
The longer the MTU, the better for performance, but the worse for reliability, because a lost packet means more data to be retransmitted and because many routers on the Internet can't deliver very long packets.
The fathers of the Internet assumed that this problem would be solved at the IP layer with IP fragmentation. Unfortunately IP fragmentation has serious disadvantages and it's avoided in practice.
Do-not-fragment bit
To work around fragmentation problems the IP layer contains a "Don't Fragment" bit on every IP packet. Continue reading
A Baker’s Dozen, 2014 Edition
As is our annual tradition, this blog provides a year-end review of how the Internet providers at the top of our IP Transit Intelligence global rankings (formerly, Renesys’ Market Intelligence) fared over the previous year. The structure and performance of the Internet remains a huge blind spot for most enterprises, even those critically dependent on it for business operations. Whether it’s the next 3 billion people coming online, poor performance due to suboptimal routing, or security breaches of a trust-based Internet infrastructure, Dyn provides critical insight into the structure and performance of the Internet, both real-time and historical, via its Internet Intelligence products. More importantly, our services help our customers make the changes necessary to optimize Internet availability, reliability, and reach. This blog reviews a single very small slice of our data related to the sizes of the top global players as it pertains to the markets and customers they serve.
Back in 2008, we chose to look at the 13 providers that spent at least some time in the Top Ten that year, hence the name “Baker’s Dozen“. We repeated that exercise in 2009, 2010, 2011, Continue reading
From VIRL to IOU and Back
When VIRL first came out everyone jumped on the bandwagon, including myself. Some of us have had it before it was officially released to the public. Cisco’s VIRL is really a good piece of software,...[[ Summary content only, you can read everything now, just visit the site for full story ]]
From VIRL to IOU and Back
When VIRL first came out everyone jumped on the bandwagon, including myself. Some of us have had it before it was officially released to the public. Cisco’s VIRL is really a good piece of software,...[[ Summary content only, you can read everything now, just visit the site for full story ]]
From VIRL to IOU and Back
When VIRL first came out everyone jumped on the bandwagon, including myself. Some of us have had it before it was officially released to the public. Cisco’s VIRL is really a good piece of software,...[[ Summary content only, you can read everything now, just visit the site for full story ]]
Data-Driven RESTful API Testing for Java
This post is a Zombie that I'm resurrecting from my drafts. I"m not doing any Java these days, but hopefully this post might be useful to somebody
In my quest to get better code coverage for the OVSDB project in OpenDaylight I started to look at increasing coverage for the REST API. It's pretty difficult to test this in an efficient way (lines of code) and frameworks like Robot would have been easier to use. The disadvantage with using an external test framework is that code coverage (using a plugin like JaCoCo) would not be logged. Therefore I harnessed my Junit-Jitsu and found a solution that lives in the JVM
The Scenario
Lets take a very simple example REST API
GET, PUT: /v2/foo
Step 1: The Solution Components
The solution uses the following components
- JUnit Parameterized Test Runner
- YAML
- Jersey Client
The parameterized runner will run run a test multiple times given a bunch of parameters. This way we can write one test, specifiy our parameters in YAML and let JUnit do the hard work!
Step 2: Writing the YAML file
Here's a sample YAML file:
---
- name: testGetAllFoo
operation: GET
uri Continue readingData-Driven RESTful API Testing for Java
This post is a Zombie that I'm resurrecting from my drafts. I"m not doing any Java these days, but hopefully this post might be useful to somebody
In my quest to get better code coverage for the OVSDB project in OpenDaylight I started to look at increasing coverage for the REST API. It's pretty difficult to test this in an efficient way (lines of code) and frameworks like Robot would have been easier to use. The disadvantage with using an external test framework is that code coverage (using a plugin like JaCoCo) would not be logged. Therefore I harnessed my Junit-Jitsu and found a solution that lives in the JVM
Combining MPLS/VPN, MPLS-TE and QoS on MPLS Talks
In the final part of our MPLS-focused discussion, Seamus wanted to know how one could combine MPLS/VPN, MPLS-TE and QoS (for example, sending VoIP traffic for one customer over a different path).
Short answer: don’t even think about doing that. The added complexity is not worth whatever extra money you’ll be charging the customer (or not).
From VIRL to IOU and Back
When VIRL first came out everyone jumped on the bandwagon, including myself. Some of us have had it before it was officially released to the public. Cisco’s VIRL is really a good piece of...[[ Summary content only, you can read everything now, just visit the site for full story ]]
Networking Field Day 9: First look- Monitor the network with NetBeez?!
With Networking Field Day #9 quickly approaching, I can’t help but start digging into the presenters and see what they currently offer. In reviewing the presenters at Networking Field Day #9, one of them NetBeez offers an interesting take on network monitoring. I must admit this is one of the presenters I needed to do a little […]
Data-Driven RESTful API Testing for Java
This post is a Zombie that I'm resurrecting from my drafts. I"m not doing any Java these days, but hopefully this post might be useful to somebody
In my quest to get better code coverage for the OVSDB project in OpenDaylight I started to look at increasing coverage for the REST API. It's pretty difficult to test this in an efficient way (lines of code) and frameworks like Robot would have been easier to use. The disadvantage with using an external test framework is that code coverage (using a plugin like JaCoCo) would not be logged. Therefore I harnessed my Junit-Jitsu and found a solution that lives in the JVM
Cisco MDS Port-Security with Auto-Learning
I have been learning about Cisco MDS port-security recently and I have been struggling with this feature because it was different from what I expected. What I was expecting was something very similar (and easy) like the good old Ethernet Port-Security feature. This is clearly not the case and I will show you how to […]Why Network Engineering Is a Top Job for 2015
Why Network Engineering Is a Top Job for 2015
by Brian Boyko, Contributor - February 3, 2015
According to career marketplace Glassdoor, one of the top 25 best jobs in America for 2015 is “network engineer.” No surprises here. Network engineering is a high growth industry: interesting and challenging work, tons of autonomy in how to solve problems and come up with solutions, well paying, and most importantly, the knowledge that you’re building something and bringing creations to life.
Indeed, the complexities of modern networks make network engineers indispensable, with the mix of virtual and real servers, cloud services and data centers, and of course, the integration of SDN into your network. On a good day, you get that rush of power from doing what is essentially mad science.
It should be noted that network engineering was one of eight IT-based jobs to crack the top 25. Clearly, technical skills are in demand.
You know, it brings me back to Nicholas Carr’s books “Does IT Matter?” and “The Big Switch,” which expanded on a 2003 article he wrote in Harvard Business Review claiming that “IT Doesn’t Matter.” Essentially, Carr predicted Continue reading
NFD8 Recap: Nuage Networks – One to Watch
Last fall, I attended the Tech Field Day NFD8 event, and one of the presenting companies was Nuage Networks. This was actually the second time I’d seen Nuage present at an NFD event, the first one being NFD6 a year earlier. Upon my return from NFD8, I did a short write-up of each presenting sponsor for my coworkers at H.A. Storage Systems to keep them informed. The following is my recap of Nuage Networks after their presentation in which I explain why I think Nuage is really on-target with their SDN solution and is definitely a solution to keep an eye on.
Nuage Networks is definitely an SDN company to watch. They are a subsidiary of Alcatel-Lucent (sort of like Cisco’s Insieme but apparently there are no current plans to spin them back in), so they have good financial backing — better than many startups. They have a very mature vision of complete end-to-end SDN with automated deployment tools and fabric-wide management, but they’ve gone beyond what several of the competitors have to look at massive, massive scaling as a core requirement.
Rather than using VXLAN or some other new protocol for things like federation between fabrics, they simply use Continue reading
Binary Metal Guitar
Thank you Ed for sharing the video the led me to find this…
The post Binary Metal Guitar appeared first on Router Jockey.
The Cisco Network Programmability (SDN) Intro Course
Four network programmability certs, two exams for each cert (with matching video courses for each exam) – plus one introductory video. Today’s post discusses that introductory video course, namely:
- Introducing Network Programmability Fundamentals
No muss, no fuss – jump into the post for more details.
Overview
Cisco recommends their “Introducing Network Programmability Fundamentals” course to anyone who is:
- New to SDN
- New to network programmability
Basically, before diving into the other exams and courses, this introductory course sets the stage. Do you have to watch it to get the certifications? No. Can you benefit? Sure. But if you do want to use this course, take it first in sequence, before taking the other Cisco network programmability courses.
Figure 1: Big (and Obvious) Progression from the Introductory Course
Covering the bases, this list gives the highlights of the course:
- Six videos of approximately 1 hour each
- Six different presenters (one per video)
- 6 month lease
- $59 (at least when I looked just now)
- No exam associated with the course – it’s just fundamental background
- My recollection (with no way to confirm) is that the version of the course I see when writing this post came out late 2013.
NBase-ing Your Wireless Decisions
Copper is heavy. I’m not talking about it’s atomic weight of 63 or the fact that bundles of it can sag ceiling joists. I’m talking about the fact that copper has inertia. It’s difficult to install and even more difficult to replace. Significant expense is incurred when people want to run new lines through a building. I never really understood how expensive a proposition that was until I went to work for a company that run copper lines.
Out of Mind, Out of Sight
According to a presentation that we saw at Tech Field Day Extra at Cisco Live Milan from Peter Jones at Cisco, Category 5e and 6 UTP cabling still has a significant install base in today’s organizations. That makes sense when you consider that 5e and 6 are the minimum for gigabit Ethernet. Once we hit the 1k mark with speeds, desktop bandwidth never really increased. Ten gigabit UTP Ethernet is never going to take off outside the data center. The current limitations of 10Gig over Cat 6 makes it impossible to use in a desktop connectivity situation. With a practical limit of around 50 meters, you practically have to be on top of the IDF closet Continue reading
Decision Time for the Open Internet
On February 26 of this year the Federal Communications Commission of the United States will vote on a proposed new ruling on the issue of "Network Neutrality" in the United States, bringing into force a new round of measures that are intended to prevent certain access providers from deliberately differentiating service responses on the carriage services that they provide.The Cisco Network Programmability (SDN) Intro Course
Four network programmability certs, two exams for each cert (with matching video courses for each exam) – plus one introductory video. Today’s post discusses that introductory video course, namely:
- Introducing Network Programmability Fundamentals
No muss, no fuss – jump into the post for more details.
Overview
Cisco recommends their “Introducing Network Programmability Fundamentals” course to anyone who is:
- New to SDN
- New to network programmability
Basically, before diving into the other exams and courses, this introductory course sets the stage. Do you have to watch it to get the certifications? No. Can you benefit? Sure. But if you do want to use this course, take it first in sequence, before taking the other Cisco network programmability courses.
Figure 1: Big (and Obvious) Progression from the Introductory Course
Covering the bases, this list gives the highlights of the course:
- Six videos of approximately 1 hour each
- Six different presenters (one per video)
- 6 month lease
- $59 (at least when I looked just now)
- No exam associated with the course – it’s just fundamental background
- My recollection (with no way to confirm) is that the version of the course I see when writing this post came out late 2013.