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Category Archives for "Russ White"

The Design Mindset (1)

How does a network designer, well, actually design something? What process do you use as a designer to get from initial contact with a problem to building a new design to deploying a solution? What is the design mindset? I’ve been asking myself just this question these last few months, going through old documentation to see if I can find a pattern in my own thinking that I could outline in a way that’s more definite than just “follow my example.” What I discovered is my old friends the OODA loop and the complexity model are often in operation.

So, forthwith, a way to grab hold of a designer mindset, played out in an unknown number of posts.

Begin with observe. Observation is the step we often skip, because we’ve either worked on the network for so long “we don’t need to,” or we’re “so experienced we know what to look for.” This is dangerous. Let me give you an example.

ooda-complexityA long time ago, in a small shire on the borders of reality (it seems now), I worked on a piece of equipment we called the funnyman. Specifically, this was the FNM-1, which was used to detect runway Continue reading

Research ‘net: The TEMPEST edition

When I was in the US Air Force, as part of the 438th Communications Group, we had a Group Readiness Center that contained a large board with the airfield equipment status, a safe with various drawers with different classification levels, a couple of encrypted communication systems, and… a couple of strange looking Z200 computers. The screen on these computers were covered with a fine mesh, and the power cables ran through a special cleaning box. What was the point of all this fanciness?research-net

TEMPEST. The ability to gather information about what’s on a computer’s screen by examining the signals transmitted (unintentionally) from the monitor screen, power cable, and other electronics. This might seem odd, but essentially any wire is an antenna that can (and will) carry information from a computer; at some range, these signals can be detected and deciphered in a way that allows you to determine what the computer is processing. Screens are more fruitful, as the older style Cathode Ray Tube (CRT) displays essentially shoot a stream of electrons onto a piece of glass, some of which must leak, and hence can be picked up and decoded to see what’s on the screen from quite a distance Continue reading

Slicing and Dicing Flooding Domains (2)

The first post in this series is here.

Finally, let’s consider the first issue, the SPF run time. First, if you’ve been keeping track of the SPF run time in several locations throughout your network (you have been, right? Right?!? This should be a regular part of your documentation!), then you’ll know when there’s a big jump. But a big jump without a big change in some corresponding network design parameter (size of the network, etc.), isn’t a good reason to break up a flooding domain. Rather, it’s a good reason to go find out why the SPF run time changed, which means a good session of troubleshooting what’s probably an esoteric problem someplace.

Assume, however, that we’re not talking about a big jump. Rather, the SPF run time has been increasing over time, or you’re just looking at a particular network without any past history. My rule of thumb is to start really asking questions when the SPF run time gets to around 100ms. I don’t know where that number came from—it’s a “seat of the pants thing,” I suppose. Most networks today seem to run SPF in less than 10ms, though I’ve seen a few that Continue reading

Reaction: BGP convergence, divergence & the ‘net

Let’s have a little talk about BGP convergence.

We tend to make a number of assumptions about the Internet, and sometimes these assumptions don’t always stand up to critical analysis. . . . On the Internet anyone can communicate with anyone else – right? -via APNIC

Geoff Huston’s recent article on the reality of Internet connectivity—no, everyone cannot connect to everyone—prompted a range of reactions from various folks I know.

For instance, BGP is broken! After all, any routing protocol that can’t provide basic reachability to every attached destination must be broken, right? The problem with this statement is it assumes BGP is, at core, a routing protocol. To set the record straight, BGP is not, at heart, a routing protocol in the traditional sense of the term. BGP is a system used to describe bilateral peering arrangements between independent parties in a way that provides loop free reachability information. The primary focus of BGP is not loop free reachability, but policy.

After all, BGP convergence is a big deal, right? Part of the problem here is that we use BGP as a routing protocol in some situations (for instance, on data center fabrics), so we have a hard time adjusting our thinking Continue reading

DoS’ing your mind: Controlling information inflow

Everyone wants your attention. No, seriously, they do. We’ve gone from a world where there were lots of readers and not much content, to a world where there is lots of content, and not many readers. There’s the latest game over here, the latest way to “get 20,000 readers,” over there, the way to “retire by the time you’re 32” over yonder, and “how to cure every known disease with this simple group of weird fruit from someplace you’ve never heard of (but you’ll certainly go find, and revel in the pictures of perfectly healthy inhabitants now),” naggling someplace at the back of your mind.

The insidious, distracting suck of the Internet has become seemingly inescapable. Calling us from our pockets, lurking behind work documents, it’s merely a click away. Studies have shown that each day we spend, on average, five and a half hours on digital media, and glance at our phones 221 times. -via connecting

Living this way isn’t healthy. It reduces your attention span, which in turn destroys your ability to get anything done, as well as destroying your mind. So we need to stop. “Squirrel” is funny, but you crash planes. “Shiny thing” is funny, but Continue reading

New Address

To make this blog a little easier to find, I’ve pointed rule11.us here as well. ntwrk.guru will continue to work, as well, but people seem to have a hard time remembering the url, so I added a second one.

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