Reader Comments: Spanning Tree Woes

My latest spanning tree protocol (STP) posts generated numerous comments, some of them so relevant that I decided to summarize them into another blog post.

Weird Things Happen

The unidirectional link scenario mentioned by Antonio is pretty well known:

How Realistic Is High-Density Virtualization?

A while ago I guestimated that most private clouds don’t have more than a few thousand VMs, and that they don’t need more bandwidth than what two ToR switches could provide.

Last autumn Iwan Rahabok published a blog post describing the compute- and storage parts of it, and I had a presentation describing the networking aspects of high-density consolidation. However…

Video: PCEP Deep Dive

After explaining the basics of BGP-LS and PCEP, and a quick deep dive into BGP-LS, Julian Lucek focused on the second topic of his excellent webinar and described the details of Path Computation Element Protocol (PCEP).

Data Center Fabrics and SDN

A few days ago Inside-IT published an interview Christoph Jaggi did with me. In case you don’t understand German, here’s the English version of it.

There is a lot of talk about data center fabrics. What problem do they try to solve?

The data center fabrics are supposed to solve a simple-to-define problem: building a unified data center infrastructure that seamlessly supports data and storage communications. As always, the devil hides in the details.

You Want Your Network to Be like Google’s? Really?

This article was initially sent to my SDN mailing list. To register for SDN tips, updates, and special offers, click here.

During one of my SDN workshops one of the attendees working for a mid-sized European ISP asked me this question:

Our management tells us we should build our network like Google does, including building our own switches. Where should we start?

The only answer I could give him was “You don’t have a chance.”

Spanning Tree Protocol (STP) and Bridging Loops

Continuing our bridging loops discussion Christoph Jaggi sent me another question:

Theoretically STP should avoid bridging loops, and yet you claim they cause data center meltdowns. What am I missing?

In theory, STP avoids bridging loops. In practice, there are numerous reasons STP got a bad name.

Greg Ferro on Private and Public Clouds

Everyone talks about public or hybrid clouds, whitebox switching with home-grown networking operating system, or SDN nirvana, but whenever I talk with enterprise-focused architects, consultants or vendor SEs, I see a totally different story.

Here's a typical response I'm getting from engineers in this group: “I work with multinational financial customers, and in this group hybrid cloud is not even a topic. They do private cloud projects, with some of them looking into public cloud deployments of isolated projects on base AWS functionality.”

Troubleshoot Your Network with PacketDesign on Software Gone Wild

Imagine you get a routing outage in your network resulting in three minutes of traffic blackholing. After a few tense minutes it goes away and life is good, but you desperately want to know what went wrong. Can you figure it out? Well, you could if you were using PacketDesign tools, as Cengiz Alaettinoglu explained on Episode 51 of Software Gone Wild.

Update#1: Leaf-and-Spine Fabric Designs

I somewhat expected that the leaf-and-spine fabrics designs webinar won’t be as short as I initially planned it to be, but when I started developing the scenarios and talking with guest speakers the whole thing exploded into a four-session saga (or maybe we’ll end up with the fifth session of a four-part trilogy).

Here’s a short update on what’s planned and where we are at the moment:

VLANs and Failure Domains Revisited

My friend Christoph Jaggi, the author of fantastic Metro Ethernet and Carrier Ethernet Encryptors documents, sent me this question when we were discussing the Data Center Fabrics Overview workshop I’ll run in Zurich in a few weeks:

When you are talking about large-scale VLAN-based fabrics I assume that you are pointing towards highly populated VLANs, such as VLANs containing 1000+ Ethernet addresses. Could you provide a tipping point between reasonably-sized VLANs and large-scale VLANs?

It's not the number of hosts in the VLAN but the span of a bridging domain (VLAN or otherwise).

What They Said: vSphere 6 Networking Deep Dive

One of the engineers watching the vSphere 6 Networking Deep Dive found it particularly useful:

There were pearls of knowledge in there which expanded my understanding of ESX and gave me more than a few "aha!" moments […] The course is worth the money and time for sections "uplink redundancy & load balancing" and "VLAN based virtual networks" alone.

Not convinced? Check out other reviews and survey results.

Why Would You Need BGP-LS and PCEP?

My good friend Tiziano Tofoni (the organizer of wonderful autumn seminars in Rome) sent me these questions after attending the BGP-LS and PCEP Deep Dive webinar, starting with:

Are there real use cases for BGP-LS and PCEP? Are they really useful? Personally I do not think they will ever be used by ISP in their (large) networks.

There are some ISPs that actually care about the network utilization on their expensive long-distance links.

BGP-LS Deep Dive

After explaining why you’d want to use BGP-LS and PCEP in your network, Julian Lucek did a quick deep dive into the intricacies of BGP-LS, including printouts relating BGP-LS updates to IS-IS topology database.

This part of the PCEP/BGP-LS webinar is already public, to watch the rest of it fill in a short form on the webinar description page.

ASICs Behind the Scenes

A lot of people love to talk about ASICs and merchant silicon, but very few really understand the basics. Now there’s a quick way to fix that: watch the excellent Tech Field Day video with Dave Zacks from Cisco Systems.

Running BGP on Servers

Mr. A. Anonymous left this comment on my BGP in the data centers blog post:

BGP is starting to penetrate into servers as well. What are your thoughts on having BGP running from the servers themselves?

Finally some people got it. Also, welcome back to the '90s (see also RFC 1925 section 2.11).

Full Stacks and S-Curves

Here’s another interesting coincidence:

• A few days ago I listened to excellent Full Stack Journey podcast with Scott Lowe and Matt Oswalt in which they discussed how some engineers fear moving into adjacent technologies because they would have to (yet again) start from scratch;
• This morning I was cleaning up some old presentations and stumbled upon a diagram I’ve “never seen before” (in the middle of a presentation I created – how’s that for reliable memory) which led me to an interesting article explaining how we have to jump into unknown territories to retain the thrill we get from mastering new skills.

Homework for today: listen to the podcast, read the article, and start exploring some new technology (network automation immediately comes to mind).

Dear $Vendor Reps, Align Your SDN Story with Reality

A while ago someone posted a link to an article that links to LinkedIn’s blog post describing their switch-building efforts to the LinkedIn SDN group (how’s that for a circular reference?), and a consultant from Brocade felt compelled to share his wisdom with the world. Unfortunately he got most of the facts wrong.

Full-stack Engineers are going mainstream

They made it all the way to Dilbert ;)

Source: Dilbert.com

How Money Spoiled Blogging

Found this on Quora:

Money spoiled blogging. Why? Because people moved from doing great things for money and then talking about them on their free blogs, to people doing nothing but talking on their monetized blogs.

It’s not just blogs, and it’s not just cooking (the author's focus).

New Webinar: Leaf-and-Spine Fabric Designs

Several subscribers told me they’d need more details on leaf-and-spine fabric designs. As they say: your wish is my command – the upcoming update session of the leaf-and-spine fabric architectures webinar will have more details on all possible combinations of layer-2 and layer-3 fabrics.

The first session (on March 3rd) will cover layer-3 fabrics. We’ll start with the basics: