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The Why of Things

Growing up, I was labeled a “bright” kid by my teachers and family. But I always had one big problem: If I didn’t understand something I would get really frustrated. As in, suppress the urge to go outside and break a two by four in half frustrated. Most classwork came so easily to me that I was not very prepared for the times when I didn’t fully comprehend something right away.

I haven’t felt that way very much since leaving school for the working world, but CIDR notation is making me feel that way again for the first time in a long time. CIDR notation is basically a way of describing IP ranges and also figuring out their broadcast and subnet masks. I’ve spent a few hours today trying to figure this out and all I’ve accomplished so far is a battle to keep myself from going outside to find that old friend the two by four.

In case you’re wondering, no, I’ve never actually broken a two by four in half out of frustration. It sure SOUNDS like a fun way to work it out though.

Here’s my real problem: The best way I can wrap my head around something is to know WHY it exists in the first place. What is it there for? What is the purpose? I understand how IP addresses work in the basic sense, which is why the complicated CIDR setup seems completely pointless to me. All IPs, unless you’re inside a network using NAT, are unique. So it really seems to me like someone created this entire system as a lazy way of distributing IP ranges. How hard is it to say, for example, 69.200.100.10 – 69.200.100.15? Why does there need to be this huge complex system?

Bueller?

All I’m getting so far is “it works this way because this other part means or does such and such” but what I need to know is WHY it’s necessary for that “such and such” to be happening in the first place.

Considering DNS is supposed to have roots in math, statements like this one drive me crazy:

indicating prefix length with a suffix

It’s either a prefix or a suffix, not both. This reminds me of my psychology classes where they tried to describe behavioral tendencies using mathematic formulas, and when I asked the professor about solving such a formula I was basically told you couldn’t.

Update: Many, many thanks to Mike Neir for giving me an explanation that, while it doesn’t make me feel like an expert, has at least answered my initial “big picture” questions and has set me on the path to really understanding it. Thanks Mike, you rule.

Categories: life, network, work Tags: , ,
  1. April 4th, 2008 at 21:11 | #1

    More info if you want it.. While in the bathroom^H^H^H^H^H^H^H^H^H^ my office, I was thinking about the logical stuff I was talking to you about. Here’s the basic routing decision I hinted at: if ($IP logicalAND $SubnetMask) equals $NetworkAddress, then $IP is in the network defined by $NetworkAddress and a netmask of $SubnetMask.

    Routing priority (almost) always goes from the most specific choices that match the routing decision (those with the largest prefix numbers, and therefore the smaller subnets) to the least specific (smaller prefix numbers, larger networks). So if you’re looking at a hypothetical routing table like so:
    10.0.0.0/24 routes out eth0
    10.0.0.0/16 routes out eth1
    10.0.0.0/8 routes out eth2
    default gateway 10.254.254.254, via eth2

    If you wanted to route to 10.0.0.1, you’d have three options, but the path via eth0 would be chosen because it’s most specific. If you wanted to route to 10.0.1.1, your eth0 path wouldn’t match, so it would take eth1, because it’s more specific than the eth2 path, even though both match. Trying route to 10.1.0.1 wouldn’t match either eth0 or eth1’s path, so eth2 would be chosen. Destinations that don’t match any of the defined routes get tossed at the default gateway.

    There you go… More helpful information on how CIDR is useful. Not only does it define networks, but most (if not all) devices using TCP/IP use the CIDR calculations in routing decisions as well.

  2. gerry
    June 12th, 2008 at 18:35 | #2

    More important is what you can explain by what exactly is the meaning of the why question.

    Is it only relevant to ask the why of events from intelligent free acting beings like presumably humans for an example, or is it also relevant to ask the why of events from non-intelligent entities like stones and presumably non-intelligent plants and animals?

    This is the question I like to read from you about, but you brought it up and never expatiate on it.

    Think about it and write about it again, this time more productively as to enlighten me on what is the why of things.

    And when you do, please notify me, gertes(at)hotmail.com.

    I just hope you don’t disappoint me: the better part of intelligence is not only to ask questions but also and specially to attempt an explanation with one’s intelligence and mastery of ideas and experiences of the world.

    gerry

  3. tyler
    July 7th, 2008 at 15:33 | #3

    NEEEEEERRDD!!!!!!!!!!!!!

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