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Category Archives for "Russ White"

Reaction: Should routing react to the data plane?

Over at Packet Pushers, there’s an interesting post asking why we don’t use actual user traffic to detect network failures, and hence to drive routing protocol convergence—or rather, asking why routing doesn’t react to the data place.

I have been looking at convergence from a user perspective, in that the real aim of convergence is to provide a stable network for the users traversing the network, or more specifically the user traffic traversing the network. As such, I found myself asking this question: “What is the minimum diameter (or radius) of a network so that the ‘loss’ of traffic from a TCP/UDP ‘stream’ seen locally would indicate a network outage FASTER than a routing update?”

This is, indeed, an interesting question—and ones that’s highly relevant in our current software defined/drive world. So why not? Let me give you two lines of thinking that might be used to answer this question.

First, let’s consider the larger problem of fast convergence. Anyone who’s spent time in any of my books, or sat through any of my presentations, should know the four steps to convergence—but just in case, let’s cover them again, using a slide from my forthcoming LiveLesson on IS-IS:

Convergence Steps

There Continue reading

The Design Mindset (3)

So you’ve spent time asking what, observing the network as a system, and considering what has actually been done in the past. And you’ve spent time asking why, trying to figure out the purpose (or lack of purpose) behind the configuration and design choices made in the past. You’ve followed the design mindset to this point, so now you can jump in and make like a wrecking ball (or a bull in a china shop), changing things so they’re better, and the new requirements you have can fit right in. Right?

Wrong.

As an example, I want to take you back to another part of a story I told here about my early days in the networking world. Before losing the war over Banyan Vines, I actually encountered an obstacle that should have been telling—but I was too much of a noob at the time to recognize it for the warning it really was. At the time, I had written a short paper comparing Vines to Netware; the paper was, perhaps, ten pages long, and I thought it did a pretty good job of comparing the two network operating systems. Heck, I’d even put together a page showing how Vines Continue reading

CAP Theorem and Routing

In 2000, Eric Brewer was observing and discussing the various characteristics of database systems. Through this work, he observed that a database generally has three characteristics—

  • Consistency, which means the database will produce the same result for any two readers who happen to read a value at the same moment in time.
  • Availability, which means the database can be read by any reader at any moment in time.
  • Partionability, which means the database can be partitioned.

Brewer, in explaining the relationship between the three in a 2012 article, says—

The easiest way to understand CAP is to think of two nodes on opposite sides of a partition. Allowing at least one node to update state will cause the nodes to become inconsistent, thus forfeiting C (consistency). Likewise, if the choice is to preserve consistency, one side of the partition must act as if it is unavailable, thus forfeiting A (availability).

The CAP theorem, therefore, represents a two out of three situation—yet another two out of three “set” we encounter in the real world, probably grounded someplace in the larger space of complexity. We’ll leave the relationship to complexity on the side for the moment, however, and just look at how Continue reading

Book Winners!

Lots of good suggestions in my inbox—thanks to all who gave me some great design ideas to blog about. I eventually chose two winners, as I uncovered another copy of the book to give away! The two winners are Patrick Watson and Matthew Sabin. I’m going to try and run something like this every three or four months, so look for another one in the future.

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Should We Stop Encryption? Can We?

It’s not like they’re asking for a back door for every device.
If the world goes dark through encryption, we’ll be back to the wild west!
After all, if it were your daughter who had been killed in a terrorist attack, you’d want the government to get to that information, too.

While sitting on a panel this last week, I heard all three reactions to the Apple versus FBI case. But none of these reactions ring true to me. security-net

Let’s take the first one: no, they’re not asking for a back door for every device. Under the time tested balance between privacy and government power, the specific point is that people have a reasonable expectation of privacy until they come under suspicion of wrongdoing. However, it’s very difficult to trust that, in the current environment, that such power, once granted, won’t be broadened to every case, all the time. The division between privacy and justice before the law was supposed to be at the point of suspicion. That wall, however, has already been breached, so the argument now moves to “what information should the government be able to trawl through in order to find crimes?” They are asking for Continue reading

The Design Mindset (2)

In a comment from last week’s post on the design mindset, which focuses on asking what through observation, Alan asked why I don’t focus on business drivers, or intent, first. This is a great question. Let me give you three answers before we actually move on to asking why?

Why can yuor barin raed tihs? Because your mind has a natural ability to recognize patterns and “unscramble” them. In reality, what you’re doing is seeing something that looks similar to what you’ve seen before, inferring that’s what is meant now, and putting the two together in a way you can understand. It’s pattern recognition at it’s finest—you’re already a master at this, even if you think you’re not. This is an important skill for assessing the world and reacting in (near) real time; if we didn’t have this skill, we wouldn’t be able to tolerate the information inflow we actually receive on a daily basis.network-design-mindset-01

The danger is, of course, that you’re going to see a pattern you think you recognize and skip to the next thing to look at without realizing that you’ve mismatched the pattern. These pattern mismatches can be dangerous in the real world—like the time I Continue reading