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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

Securing BGP: A Case Study (5)

BGP provides reachability for the global ‘net, as well as being used in many private networks. As a system, BGP (ultimately) isn’t very secure. But how do we go about securing BGP? This series investigates the questions, constraints, and solutions any proposal to secure BGP must deal with as a case study of asking the right questions, and working at the intersection of business and technology.

As a short review, we started off with three questions, described in the first post, each of which we’ve been considering in some detail:

  • Should we focus on a centralized solution to this problem, or a distributed one?
    • Assuming we’re using some sort of encryption to secure the information used in path validation, where do the keys come from? The fourth post considers this question.
    • Should the information used to validate paths be distributed or stored in a somewhat centralized database?
  • Should we consider solutions that are carried within the control plane, within BGP itself, or outside?
  • What is it we can actually prove in a packet switched network? This is considered in post 2 and post 3.

Here I’m going to discuss the problem of a centralized versus distributed database to carry the Continue reading