Author Archives: Ivan Pepelnjak
Author Archives: Ivan Pepelnjak
One of the few beauties of most “industry standard CLI” implementations1 is that they’re idempotent: nothing changes (apart from ACLs) if you configure the same stuff a dozen times. Most of these implementations allow you to deconfigure the same stuff multiple times; FRRouting is one of the unfortunate exceptions.
Imagine you have a bunch of IP prefixes you want to advertise with BGP. You could use network statements within the router bgp configuration to get that done:
One of the few beauties of most “industry standard CLI” implementations1 is that they’re idempotent: nothing changes (apart from ACLs) if you configure the same stuff a dozen times. Most of these implementations allow you to deconfigure the same stuff multiple times; FRRouting is one of the unfortunate exceptions.
Imagine you have a bunch of IP prefixes you want to advertise with BGP. You could use network statements within the router bgp configuration to get that done:
Can you use BGP to connect to the global Internet without having a public BGP AS number? Of course, assuming your Internet Service Provider is willing to run BGP with a network using a private AS number. But what happens if you want to connect to two ISPs? It’s ridiculous to expect you’ll be able to persuade them to use the same private AS number.
That’s one of the many use cases for the local-as functionality available in most BGP implementations. You can practice it in the Use Multiple AS Numbers on the Same Router lab exercise.
Can you use BGP to connect to the global Internet without having a public BGP AS number? Of course, assuming your Internet Service Provider is willing to run BGP with a network using a private AS number. But what happens if you want to connect to two ISPs? It’s ridiculous to expect you’ll be able to persuade them to use the same private AS number.
That’s one of the many use cases for the local-as functionality available in most BGP implementations. You can practice it in the Use Multiple AS Numbers on the Same Router lab exercise.
I stay as far away from Ansible as possible these days and use it only as a workflow engine to generate device configurations from Jinja2 templates and push them to lab devices. Still, I manage to trigger unexpected behavior even in these simple scenarios.
Ansible has a complex system of variable (fact) precedence, which mostly makes sense considering the dozen places where a variable value might be specified (or overwritten). Ansible documentation also clearly states that the extra variables (specified on the command line with the -e
keyword) have the highest precedence.
Now consider these simple playbooks. In the first one, we’ll set a fact (variable) and then print it out:
I stay as far away from Ansible as possible these days and use it only as a workflow engine to generate device configurations from Jinja2 templates and push them to lab devices. Still, I manage to trigger unexpected behavior even in these simple scenarios.
Ansible has a complex system of variable (fact) precedence, which mostly makes sense considering the dozen places where a variable value might be specified (or overwritten). Ansible documentation also clearly states that the extra variables (specified on the command line with the -e
keyword) have the highest precedence.
Now consider these simple playbooks. In the first one, we’ll set a fact (variable) and then print it out:
When I described the need to turn off the BGP AS-path loop prevention logic in scenarios where a Service Provider expects a customer to reuse the same AS number across multiple sites, someone quipped, “but that should be fixed by the Service Provider, not offloaded to the customer.”
Not surprisingly, there’s a nerd knob for that (AS override), and you can practice it in the next BGP lab exercise: Fix AS-Path in Environments Reusing BGP AS Numbers.
When I described the need to turn off the BGP AS-path loop prevention logic in scenarios where a Service Provider expects a customer to reuse the same AS number across multiple sites, someone quipped, “but that should be fixed by the Service Provider, not offloaded to the customer.”
Not surprisingly, there’s a nerd knob for that (AS override), and you can practice it in the next BGP lab exercise: Fix AS-Path in Environments Reusing BGP AS Numbers.
All the Container Network Interface videos from the Kubernetes Networking Deep Dive webinar with Stuart Charlton are now public. Enjoy!
One of the ipSpace.net subscribers sent me this question:
How could I use NSX to create a cloud-like software network layer enabling a VMware enterprise to create a public cloud-like availability zone concept within a data center (something like Oracle Cloud does)?
That’s easy: stop believing in VMware marketing shenanigans.
One of the ipSpace.net subscribers sent me this question:
How could I use NSX to create a cloud-like software network layer enabling a VMware enterprise to create a public cloud-like availability zone concept within a data center (something like Oracle Cloud does)?
That’s easy: stop believing in VMware marketing shenanigans.
Figuring out how to describe your network (also known as “create a source of truth”) is one of the most challenging tasks you’ll face when building a network automation solution (more). As always, the devil is in the details, starting with “and what exactly is The Truth?”.
We discussed those details in a lively Packet Pushers podcast with Claudia de Luna, David Sinn, Dinesh Dutt, Drew Conry-Murray and Ethan Banks. Have fun!
Figuring out how to describe your network (also known as “create a source of truth”) is one of the most challenging tasks you’ll face when building a network automation solution (more). As always, the devil is in the details, starting with “and what exactly is The Truth?”.
We discussed those details in a lively Packet Pushers podcast with Claudia de Luna, David Sinn, Dinesh Dutt, Drew Conry-Murray and Ethan Banks. Have fun!
FRR or (pre-NVUE) Cumulus Linux are the best bets if you want to run BGP labs in a resource-constrained environment like your laptop or a small public cloud instance. However, they both behave a bit differently from what one might expect from a networking device, including:
A new lab exercise covers these intricate details and will help you get fluent in configuring BGP on FRR or Cumulus Linux virtual machines or containers.
FRR or (pre-NVUE) Cumulus Linux are the best bets if you want to run BGP labs in a resource-constrained environment like your laptop or a small public cloud instance. However, they both behave a bit differently from what one might expect from a networking device, including:
A new lab exercise covers these intricate details and will help you get fluent in configuring BGP on FRR or Cumulus Linux virtual machines or containers.
A networking engineer with a picture-perfect implementation of a dual-homed enterprise site using BGP communities according to RFC 1998 to select primary- and backup uplinks contacted me because they experienced unacceptably long failover times.
They measured the failover times caused by the primary uplink loss and figured out it takes more than five minutes to reestablish Internet connectivity to their site.
A networking engineer with a picture-perfect implementation of a dual-homed enterprise site using BGP communities according to RFC 1998 to select primary- and backup uplinks contacted me because they experienced unacceptably long failover times.
They measured the failover times caused by the primary uplink loss and figured out it takes more than five minutes to reestablish Internet connectivity to their site.
All the Large Language Models videos from the AI/ML in Networking webinar with Javier Antich are now public. Enjoy!
David Bombal invited me for another annual chat last December, focusing on (what else) networking careers in 2024. The results were published a few days ago, and I was amazed at how good it turned out. I always love chatting with David; this time, his editing team did a masterful job.
David Bombal invited me for another annual chat last December, focusing on (what else) networking careers in 2024. The results were published a few days ago, and I was amazed at how good it turned out. I always love chatting with David; this time, his editing team did a masterful job.