Blog Posts in October 2013

VMware NSX: Defining the Problem

Every good data center presentation starts with redefining The Problem and my VMware NSX Architecture webinar was no exception – the first section describes Infrastructure-as-a-Service Networking Requirements.

I sprinted through this section during the live session, the video with longer (and more detailed) explanation comes from the Overlay Virtual Networking webinar.

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Cisco Modeling Lab (VIRL) behind the scenes

The first hints of VIRL started appearing around Cisco Live US 2013 where the product development team demonstrated Cisco’s take on 21st century network modeling tool. A few days ago, Omar Sultan, Joel Obstfeld and Ed Kern gave us a brief peek behind the scenes of this totally awesome tool (note to Cisco haters: I haven’t been drinking the teal Kool-Aid for a long time – this is my honest impression).

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Flow Table Explosion with OpenFlow 1.0 (And Why We Need OpenFlow 1.3)

The number of flows in hardware switches (dictated by the underlying TCAM size) is one of the major roadblocks in a large-scale OpenFlow deployment. Vendors are supposedly making progress, with Intel claiming up to 4000 12-tuple flow entries in their new Ethernet Switch FM6700 series. Is that good enough? As always, it depends.

TL&DR summary: Use switches that support OpenFlow 1.3.

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Estimating the Number of TCP Sessions per Host

Another day, another stateful debate, this time centered on the number of flows per hypervisor. Previously I guestimated 2.500 connections-per-second-per-(user-facing)gigabit and 37.500 concurrent sessions per user-facing gigabit, but wanted to align my numbers with reality before reaching any conclusions.

My web sites are way too small, so I asked a few of my friends to help me get more realistic figures.

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Why is IPsec so Complex?

Jason Edelman wrote a great blog post after watching Ethan Banks struggle with yet another multi-vendor IPsec deployment. Some of his ideas make perfect sense (wiki-like web site documenting working configurations between vendor X and Y for every possible X and Y), others less so (tunnel broker – particularly in view of recent Tor challenges), but let’s step back a bit and ask ourselves “Why is IPsec so complex?

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Forwarding Models in OpenFlow Networks

OpenFlow is a simple TCAM programming protocol, and can be used to implement any network forwarding paradigm as long as:

  • OpenFlow specifications include matches and actions (including rewrites) of the packet header fields used in the forwarding paradigm. For example, you cannot program SRv6 tunnels with OpenFlow because it’s not part of OpenFlow standard.
  • The forwarding hardware you want to use supports the OpenFlow matches and actions you need in your forwarding paradigm.
  • The forwarding paradigm does not use dynamic interfaces (example: MPLS-TE tunnels) or multipoint tunnel interfaces (example: VXLAN). OpenFlow was designed to be used on point-to-point physical interfaces and does not include interface management.

This blog post describes some of the more common OpenFlow use cases (assuming you want to use an obsolete rarely-implemented protocol).

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Exception Routing with BGP: SDN Done Right

One of the holy grails of data center SDN evangelists is controller-driven traffic engineering (throwing more leaf-and-spine bandwidth at the problem might be cheaper, but definitely not sexier). Obviously they don’t call it traffic engineering as they don’t want to scare their audience with MPLS TE nightmares, but the idea is the same.

Interestingly, you don’t need new technologies to get as close to that holy grail as you wish; Petr Lapukhov got there with a 20 year old technology – BGP.

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Can BGP Route Reflectors Really Generate Forwarding Loops?

TL&DR Summary: Yes (if you’re clumsy enough).

A while ago I read Impact of Graceful IGP Operations on BGP – an article that described how changes in IGP topology result in temporary (or sometimes even permanent) forwarding loops in networks using BGP route reflectors.

Is the problem real? Yes, it is. Could you generate a BGP RR topology that results in a permanent forwarding loop? Yes. It’s not that hard.

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Overlay Virtual Networks 101

My keynote speech @ PLNOG11 conference was focused on (surprise, surprise) overlay virtual networks and described the usual motley crew: The Annoying Problem, The Hated VLAN, The Overlay Unicorn, The Control-Plane Wisdom and The Ever-Skeptic Use Case. You can view the presentation on my web site; PLNOG organizers promised video recording in mid-October.

Just in case you’re wondering why I keep coming back to PLNOG: they’re not only as good as ever; they’re getting even more creative.

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OpenStack Quantum (Neutron) Plug-In: There Can Only Be One

OpenStack seems to have a great architecture: all device-specific code is abstracted into plugins that have a well-defined API, allowing numerous (more or less innovative) implementations under the same umbrella orchestration system.

Looks great in PowerPoint, but to an uninitiated outsider looking at the network (Quantum, now Neutron) plugin through the lenses of OpenStack Neutron documentation, it looks like it was designed by either a vendor or a server-focused engineer using NIC device driver concepts.

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