Category: Fabric

I was focused on network automation this week, starting with a 2-day workshop and continuing with an overview of real-life automation wins. Let’s end the week with another automation story: automated data center fabric deployment demonstrated by Dinesh Dutt during his part of Network Automation Use Cases webinar.

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The first car I got decades ago was a simple mechanical beast – you’d push something, and a cable would make sure something else moved somewhere. I could also fix 80% of the problems, and people who were willing to change spark plugs and similar stuff could get to 90+%.

Today the cars are distributed computer systems that nobody can fix once they get a quirk that is not discoverable with level-1 diagnostic tools.

I had an interesting “how do you build a small fabric without throwing every technology in the mix” discussion with Nicola Modena and mentioned that I don’t see a reason to use EVPN in fabrics with just a few switches. He disagreed and gave me a few good scenarios where EVPN might be handy. Before discussing them let’s establish a baseline.

The Setup

Assume you’re building two small data center fabrics (small because you have only a few hundred VMs and two because of redundancy and IT auditors).

After describing the basics of internal data center switch architectures, JR Rivers focused on the crux of the problem the vendors copiously exploit to create a confusopoly: is it better to use big- or small-buffer switches?

EVPN is one of the major reasons we’re seeing BGP used in small and mid-sized data center fabrics. In theory, EVPN is just a BGP address family and shouldn’t impact your BGP design. However, suboptimal implementations might invalidate that assumption.

I've described a few EVPN-related BGP gotchas in BGP in EVPN-Based Data Center Fabrics, a section of Using BGP in Data Center Leaf-and-Spine Fabrics article.

I haven’t done an update on what Avaya was doing in the data center space for years, so I asked my good friend Roger Lapuh to do a short presentation on:

• Avaya’s data center switches and their Shortest Path Bridging (SPB) fabric;
• SPB fabric features;
• Interesting use cases enabled by SPB fabric.

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A while ago (in the time of big-versus-small buffers brouhaha), I asked JR Rivers to do a short presentation focusing on buffering requirements of data center switches. He started by describing typical buffer architectures you might find in data center switches.

A while ago I helped a large enterprise redesign their data center fabric. They did a wonderful job optimizing their infrastructure, so all they really needed were two switches in each location.

Some vendors couldn’t fathom that. One of them proposed to build a “future-proof” (and twice as expensive) leaf-and-spine fabric with two leaves and two spines. On top of that they proposed to use EBGP as the only routing protocol because draft-lapukhov-bgp-routing-large-dc – a clear case of missing the customer needs.

One of my readers was so delighted that something finally happened after I wrote about a NX-OS bug that he sent me a pointer to another one that has been pending for a long while, and is now officially terminated as FAD (Functions-as-Designed… even documented in the Further Problem Description).

Here’s what he wrote (slightly reworded)…

One of my friends wanted to design a nice-and-easy layer-3 leaf-and-spine fabric for a new data center, and got blindsided by a hyperconverged vendor. Here’s what he wrote:

We wanted to have a spine/leaf L3 topology for an NSX deployment but can’t do that because the Nutanix servers require L2 between their nodes so they can be in the same cluster.

I wanted to check his claims, but Nutanix doesn’t publish their documentation (I would consider that a red flag), so I’m assuming he’s right until someone proves otherwise (note: whitepaper is not a proof of anything ;).