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Category Archives for "ipSpace.net"

netsim-tools: Network Topology Graphs

Someone using my netsim-tools sent me an intriguing question: “Would it be possible to get network topology graphs out of the tool?

Please note that we’re talking about creating graphs out of network topology described as a YAML data structure, not a generic GUI or draw my network tool. If you’re a GUI person, this is not what you’re looking for.

I did something similar a long while ago for a simple network automation project (and numerous networking engineers built really interesting stuff while attending the Building Network Automation Solutions course), so it seemed like a no-brainer. As always, things aren’t as easy as they look.

netlab Network Topology Graphs

A netlab user sent me an intriguing question: “Would it be possible to get network topology graphs out of the tool?

Please note that we’re talking about creating graphs out of network topology described as a YAML data structure, not a generic GUI or draw my network tool. If you’re a GUI person, this is not what you’re looking for.

I did something similar a long while ago for a simple network automation project (and numerous networking engineers built really interesting stuff while attending the Building Network Automation Solutions course), so it seemed like a no-brainer. As always, things aren’t as easy as they look.

Interesting Concept: Time Dilation

I loved the Time Dilation blog post by Seth Godin. It explains so much, including why I won’t accept a “quick conf call to touch base and hash out ideas” from someone coming out of the blue sky – why should I be interested if they can’t invest the time to organize their thoughts and pour them into an email.

The concept of “creation-to-consumption” ratio is also interesting. Now I understand why I hate unedited opinionated chinwagging (many podcasts sadly fall into this category) or videos where someone blabbers into a camera while visibly trying to organize their thoughts.

Just FYI, these are some of the typical ratios I had to deal in the past:

Interesting Concept: Time Dilation

I loved the Time Dilation blog post by Seth Godin. It explains so much, including why I won’t accept a “quick conf call to touch base and hash out ideas” from someone coming out of the blue sky – why should I be interested if they can’t invest the time to organize their thoughts and pour them into an email.

The concept of “creation-to-consumption” ratio is also interesting. Now I understand why I hate unedited opinionated chinwagging (many podcasts sadly fall into this category) or videos where someone blabbers into a camera while visibly trying to organize their thoughts.

Just FYI, these are some of the typical ratios I had to deal in the past:

LSA/LSP Flooding in OSPF and IS-IS

Peter Paluch loves blogging in microchunks on Twitter ;) This time, he described the differences between OSPF and IS-IS, and gracefully allowed me to repost the explanation in a more traditional format.


My friends, I happen to have a different opinion. It will take a while to explain it and I will have to seemingly go off on a tangent. Please have patience. As a teaser, though: The 2Way state between DRothers does not improve flooding efficiency – in fact, it worsens it.

LSA/LSP Flooding in OSPF and IS-IS

Peter Paluch loves blogging in microchunks on Twitter ;) This time, he described the differences between OSPF and IS-IS, and gracefully allowed me to repost the explanation in a more traditional format.


My friends, I happen to have a different opinion. It will take a while to explain it and I will have to seemingly go off on a tangent. Please have patience. As a teaser, though: The 2Way state between DRothers does not improve flooding efficiency – in fact, it worsens it.

New: ipSpace.net Design Clinic

In early September, I started yet another project that’s been on the back burner for over a year: ipSpace.net Design Clinic (aka Ask Me Anything Reasonable in a more structured format). Instead of collecting questions and answering them in a podcast (example: Deep Questions podcast), I decided to make it more interactive with a live audience and real-time discussions. I also wanted to keep it valuable to anyone interested in watching the recordings, so we won’t discuss obscure failures of broken designs or dirty tricks that should have remained in CCIE lab exams.

New: ipSpace.net Design Clinic

In early September, I started yet another project that’s been on the back burner for over a year: ipSpace.net Design Clinic (aka Ask Me Anything Reasonable in a more structured format). Instead of collecting questions and answering them in a podcast (example: Deep Questions podcast), I decided to make it more interactive with a live audience and real-time discussions. I also wanted to keep it valuable to anyone interested in watching the recordings, so we won’t discuss obscure failures of broken designs or dirty tricks that should have remained in CCIE lab exams.

Stateful Switchover (SSO) 101

Stateful Switchover (SSO) is another seemingly awesome technology that can help you implement high availability when facing a broken non-redundant network design. Here’s how it’s supposed to work:

  • A network device runs two copies of the control plane (primary and backup);
  • Primary control plane continuously synchronizes its state with the backup control plane;
  • When the primary control plane crashes, the backup control plane already has all the required state and is ready to take over in moments.

Delighted? You might be disappointed once you start digging into the details.

Stateful Switchover (SSO) 101

Stateful Switchover (SSO) is another seemingly awesome technology that can help you implement high availability when facing a broken non-redundant network design. Here’s how it’s supposed to work:

  • A network device runs two copies of the control plane (primary and backup);
  • Primary control plane continuously synchronizes its state with the backup control plane;
  • When the primary control plane crashes, the backup control plane already has all the required state and is ready to take over in moments.

Delighted? You might be disappointed once you start digging into the details.

Configuring NSX-T Firewall with a CI/CD Pipeline

Initial implementation of Noël Boulene’s automated provisioning of NSX-T distributed firewall rules changed NSX-T firewall configuration based on Terraform configuration files. To make the deployment fully automated he went a step further and added a full-blown CI/CD pipeline using GitHub Actions and Terraform Cloud.

Not everyone is as lucky as Noël – developers in his organization already use GitHub and Terraform Cloud, making his choices totally frictionless.

Configuring NSX-T Firewall with a CI/CD Pipeline

Initial implementation of Noël Boulene’s automated provisioning of NSX-T distributed firewall rules changed NSX-T firewall configuration based on Terraform configuration files. To make the deployment fully automated he went a step further and added a full-blown CI/CD pipeline using GitHub Actions and Terraform Cloud.

Not everyone is as lucky as Noël – developers in his organization already use GitHub and Terraform Cloud, making his choices totally frictionless.

Worth Reading: Ops Questions in Software Engineering Interviews

Charity Majors published another must-read article: why every software engineering interview should include ops questions. Just a quick teaser:

The only way to unwind this is to reset expectations, and make it clear that:

  • You are still responsible for your code after it’s been deployed to production, and
  • Operational excellence is everyone’s job.

Adhering to these simple principles would remove an enormous amount of complexity from typical enterprise IT infrastructure… but I’m afraid it’s not going to happen anytime soon.

Worth Reading: Ops Questions in Software Engineering Interviews

Charity Majors published another must-read article: why every software engineering interview should include ops questions. Just a quick teaser:

The only way to unwind this is to reset expectations, and make it clear that:

  • You are still responsible for your code after it’s been deployed to production, and
  • Operational excellence is everyone’s job.

Adhering to these simple principles would remove an enormous amount of complexity from typical enterprise IT infrastructure… but I’m afraid it’s not going to happen anytime soon.

Lessons Learned: Fundamentals Haven’t Changed

Here’s another bitter pill to swallow if you desperately want to believe in the magic powers of unicorn dust: laws of physics and networking fundamentals haven’t changed (see also: RFC 1925 Rule 11).

Whenever someone is promising a miracle solution, it’s probably due to them working in marketing or having no clue what they’re talking about (or both)… or it might be another case of adding another layer of abstraction and pretending the problems disappeared because you can’t see them anymore.

You’ll need a Free ipSpace.net Subscription to watch the video.

Lessons Learned: Fundamentals Haven’t Changed

Here’s another bitter pill to swallow if you desperately want to believe in the magic powers of unicorn dust: laws of physics and networking fundamentals haven’t changed (see also: RFC 1925 Rule 11).

Whenever someone is promising a miracle solution, it’s probably due to them working in marketing or having no clue what they’re talking about (or both)… or it might be another case of adding another layer of abstraction and pretending the problems disappeared because you can’t see them anymore.

You’ll need a Free ipSpace.net Subscription to watch the video.

netsim-tools Overview

In December 2020, I got sick-and-tired of handcrafting Vagrantfiles and decided to write a tool that would, given a target networking lab topology in a text file, produce the corresponding Vagrantfile for my favorite environment (libvirt on Ubuntu). Nine months later, that idea turned into a pretty comprehensive tool targeting networking engineers who like to work with CLI and text-based configuration files. If you happen to be of the GUI/mouse persuasion, please stop reading; this tool is not for you.

During those nine months, I slowly addressed most of the challenges I always had creating networking labs. Here’s how I would typically approach testing a novel technology or software feature:

netlab Overview

In December 2020, I got sick-and-tired of handcrafting Vagrantfiles and decided to write a tool that would, given a target networking lab topology in a text file, produce the corresponding Vagrantfile for my favorite environment (libvirt on Ubuntu). Nine months later, that idea turned into a pretty comprehensive tool targeting networking engineers who like to work with CLI and text-based configuration files. If you happen to be of the GUI/mouse persuasion, please stop reading; this tool is not for you.

During those nine months, I slowly addressed most of the challenges I always had creating networking labs. Here’s how I would typically approach testing a novel technology or software feature:

Open-Source DMVPN Alternatives

When I started collecting topics for the September 2021 ipSpace.net Design Clinic one of the subscribers sent me an interesting challenge: are there any open-source alternatives to Cisco’s DMVPN?

I had no idea and posted the question on Twitter, resulting in numerous responses pointing to a half-dozen alternatives. Thanks a million to @MarcelWiget, @FlorianHeigl1, @PacketGeekNet, @DubbelDelta, @Tomm3h, @Joy, @RoganDawes, @Yassers_za, @MeNotYouSharp, @Arko95, @DavidThurm, Brian Faulkner, and several others who chimed in with additional information.

Here’s what I learned:

Open-Source DMVPN Alternatives

When I started collecting topics for the September 2021 ipSpace.net Design Clinic one of the subscribers sent me an interesting challenge: are there any open-source alternatives to Cisco’s DMVPN?

I had no idea and posted the question on Twitter, resulting in numerous responses pointing to a half-dozen alternatives. Thanks a million to @MarcelWiget, @FlorianHeigl1, @PacketGeekNet, @DubbelDelta, @Tomm3h, @Joy, @RoganDawes, @Yassers_za, @MeNotYouSharp, @Arko95, @DavidThurm, Brian Faulkner, and several others who chimed in with additional information.

Here’s what I learned:

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