Blog Posts in September 2018
Here’s one of their success stories (name changed for obvious reasons):
As I explained in a previous blog post, most leaf-and-spine best-practices (as in: what to do if you have no clue) use BGP as the IGP routing protocol (regardless of whether it’s needed) with the same AS number shared across all spine switches to implement valley-free routing.
This design has an interesting consequence: when a link between a leaf and a spine switch fails, they can no longer communicate.
For example, when the link between L1 and C1 in the following diagram fails, there’s no connectivity between L1 and C1 as there’s no valley-free path between them.
This is the fourth blog post in “thinking out loud while preparing Network Infrastructure as Code presentation for the network automation course” series. Previous posts: Network-Infrastructure-as-Code Is Nothing New, Adjusting System State and NETCONF versus REST API.
Dmitri Kalintsev sent me a nice description on how some popular Infrastructure-as-Code (IaC) tools solve the challenges I described in The CRUD Hell section of Infrastructure-as-Code, NETCONF and REST API blog post:
The fast pace of webinars continues in October 2018:
- Rachel Traylor will talk about graph theory and its relevance to reliable network design on October 8th;
- The Amazon Web Services Networking webinar will start on October 11th. The second session is planned for October 25th;
- On October 16th we’ll have the third session of VMware NSX technical deep dive (unless I manage to finish on time later today… not likely).
There are no on-site events planned until early December:
- We’ll run another on-site workshop in Zurich on December 5th . This time we’ll focus on using VXLAN and EVPN to build multi-site fabrics;
- I’ll talk about making SDN better with IPv6 on December 6th.
You can attend all upcoming webinars with an ipSpace.net webinar subscription. Online courses and on-site events require separate registration.
One of the attendees of my Building Next-Generation Data Center online course tried to figure out whether you can build larger broadcast domains with VXLAN than you could with VLANs. Here’s what he sent me:
I'm trying to understand differences or similarities between VLAN and VXLAN technologies in a view of (*cast) domain limitation.
Hardware vendors are always making their silicon more complex and feature-rich. Is that a great idea or a disaster waiting to happen? We asked Luke Gorrie, the lead developer of Snabb Switch (an open-source user-land virtual switch written in Lua) about his opinions on the topic.
TL&DL version: Give me a dumb NIC, software can do everything else.
As anyone starting their journey into AWS quickly discovers, cloud is different (or as I wrote in the description of my AWS workshop you feel like Alice in Wonderland). One of the gotchas: when you link multiple routing domains (Virtual Private Clouds – the other VPC) you have to create static routing table entries on both ends. Even worse, there’s no transit VPC – you have to build a full mesh of relationships.
The correct solution to this challenge is automation:
This is the third blog post in “thinking out loud while preparing Network Infrastructure as Code presentation for the network automation course” series. You might want to start with Network-Infrastructure-as-Code Is Nothing New and Adjusting System State blog posts.
As I described in the previous blog post, the hardest problem any infrastructure-as-code (IaC) tool must solve is “how to adjust current system state to desired state described in state definition file(s)”… preferably without restarting or rebuilding the system.
There are two approaches to adjusting system state:
Here’s a bit of good news for those of you scared of network automation replacing your jobs: even Elon Musk didn’t manage to pull it off, so I don’t think a networking vendor dabbling in intent will manage to do it (particularly considering the track record of networking vendors’ network management and orchestration systems).
You might have noticed that almost every BGP as Data Center IGP design uses the same AS number on all spine switches (there are exceptions coming from people who use BGP as RIP with AS-path length serving as hop count… but let’s not go there).
There are two reasons for that design choice:
You need at least free ipSpace.net subscription to watch his answer.
This blog post was initially sent to the subscribers of my SDN and Network Automation mailing list. Subscribe here.
It’s also interesting to note that the first three levels of intent-based networking he described match closely what we’re discussing in Building Network Automation Solutions online course and what David Barroso described in Network Automation Use Cases webinar:
This is the second blog post in “thinking out loud while preparing Network Infrastructure as Code presentation for the network automation course” series. If you stumbled upon it, you might want to start here.
An anonymous commenter to my previous blog post on the topic hit the crux of the infrastructure-as-code challenge when he wrote: “It's hard to do a declarative approach with Ansible and the nice network vendor APIs.” Let’s see what he was trying to tell us.
Last year’s experiment generated so much interest that I decided to repeat it this year: if you’re an undergraduate or Master's student and manage to persuade us that you’re motivated enough to automate the **** out of everything, you’ll get a free seat in Ansible for Networking Engineers online course.
Interested? Check out the details, and apply before October 1st.
Too old? Please spread the word ;)
Here’s a question I got from an attendee of my Building Next-Generation Data Center online course:
As far as I understood […] it is obsolete nowadays to build a new DC fabric with routing on the host using BGP, the proper way to go is to use IGP + SDN overlay. Is my understanding correct?
Ignoring for the moment the fact that nothing is ever obsolete in IT, the right answer is it depends… this time on answer(s) to two seemingly simple questions “what services are we offering?” and “what connectivity problem are we trying to solve?”.
Most blog posts generate the usual noise from the anonymous peanut gallery (if only they'd have at least a sliver of Statler and Waldorf in them), but every now and then there's a comment that's pure gold. The one made by Tony Przygienda (of RIFT fame) on Valley-Free Routing post is so good and relevant that I decided to republish it as a separate blog post. Enjoy!
He found out that renumbering IPv6 in his lab required almost four times as many changes as renumbering (outside) IPv4 in the same lab.
My cynical take on that experience: “Now that you’ve documented everything that needs to be changed, make sure it’s automated the next time ;)”
Reading academic articles about Internet-wide routing challenges you might stumble upon valley-free routing – a pretty important concept with applications in WAN and data center routing design.
If you’re interested in the academic discussions, you’ll find a pretty exhaustive list of papers on this topic in the Informative References section of RFC 7908; here’s the over-simplified version.
Following “if you can’t explain it, you don’t understand it” mantra I decided to use blog posts to organize my ideas while preparing my Networking Infrastructure as Code presentation for the Autumn 2018 Building Network Automation Solutions online course. Constructive feedback is highly appreciated.
Let’s start with a simple terminology question: what exactly is Infrastructure as Code that everyone is raving about? Here’s what Wikipedia has to say on the topic:
It's always interesting to hear all kind of reasons from people to deploy CLOS fabrics in DC in Enterprise segment typically that I deal with while they mostly don't have clue about why they should be doing it in first place. […] Usually a good justification is DC to support high amount of East-West Traffic....but really? […] Ask them if they even have any benchmarks or tools to measure that in first place :)
What he wrote proves that most networking practitioners never move beyond regurgitating vendor marketing (because that’s so much easier than making the first step toward becoming an engineer by figuring out how technology really works).