Sunday of my Life

On my shelf are two books. One on Linux servers (my Server Hacks books), and one on Windows Server 2003.

The Windows book just fell over. Linux is still standing.

Today was… hot. Very hot. Try 37 degree celsius (that’s ~98 to those of you in America-land). Despite said heat, though, I ventured into the city today, to visit one of my favourite bookstores. The Technical Bookshop. I am so glad I decided to go too. I bought three books (and have a fourth on order). At a steal, too! $10 for two of them, $20 for one. The one that’s on order I put a $20 deposit down on, and that will cost a further hundred once it comes in, but it will be worth it.

1. SAMS: Microsoft Windows Server 2003 Dealta Guide: A hand-reference book on the Windows Server 2003 platform, covering all its base capabilities. A handy guide for any aspiring network admin.
2. O’Rielly: Linux Server Hacks: This is the good kinda hack, the things that help systems run better and faster and more securely. Not the media hyped sort of hack that a mother or offshore casino might do on your bank’s systems to get at your money. That’s a crack. I do so wish the media would get the parlance right and stop villifying the innocent parties.
3. Syngress Computers: RHCE (Red Hat Certified Engineer) Study Guide: Okay, this is wonderful (or will be once I get my hands on it). I read quickly throguh the somewhat battered display copy of it today, the only one left. And I cannot wait to get my copy of it. Further study, here I come!
4. Sherrilyn Kenyon’s Character Naming Sourcebook: A bit out of step with the other books, yes, but it was a steal at $10, and a gift for my sister, who is both a big fan of Sherrilyn kenyon, and will be studying professional writing and editing in the coming year.

I am officially geeking out. So much techy goodness. Plus the look on my sister’s face when I handed the book to her was damn nice too.

May I just say, this is about one of the best examples of a funny hack I have seen for a long time. And it introduced me to a blog I’d never seen before, run by a techy. I love it. It is so linked.

In the space of two days I have managed to get out eighteen (18) job applications/résumé canvasses. I’m rather proud of myself. Now we just wait to see if any of them bear fruit. Oh, and keep doing more, of course. No stopping me now!

(Further note: Most of the applications were coherent, except for one that I accidentally attached the wrong name — which was, also, the wrong gender to the application, but I quickly sent an errata email apologising for it.)

As far as my brain is concerned there is no such thing as six in the morning. I laid out carefully, last night, everything I would need to take with me today. Keys. Wallet. Watch. Credit card (not mine). Noterised letter stating that I’m allowed to use the aforementioned credit card. Study-guide to read on the train (again). Cisco Academy connection ID. CCNA 640-801 voucher number… all nise and neat and in order. Perfect for the sleepy mind to just grab and go

Well, not quite.

I got onto the train at 7:10AM, sat down, and started reading, going over points, trying to memorise what I can (and I should have learnt my lesson by now, studying on the day never helps me at all. I tend to start forgetting things, then). I never suspected, not thorguh the hour long trip up to Caulfield, nor through the 15 minute wait for the next Frankston train, or even through the 40 minute trip down to Frankston. I had left two crucial things at home. My academy connection ID, and my CCNA voucher number. Without these I can’t take the exam or, even if I could, get my discount.

Luckily they let me call home, and I woke up Erin, who told me what I needed to know, and so I could take the exam at a 50% discount. So, crisis solved. And I’m drained, completely, now. I barely slept last night, on the go since early in the morning, and it’s nearly 4PM now.

Addendum: Oh, and I passed by the way. Just barely. I needed 849 out of 1000, and I got 857. But I passed. I told you my brain was asleep!

VLSM, or Variable Length Subnet Masks is a by-product of the advanced routing concepts of such routing protocols as IS-IS, OSPF, EIGRP and RIP version 2, called Classless Inter-Domain Routing (or CIDR, Cider, get it?). At its most simlistic VLSM allows you to take an already subnetted network, and subnet one or more of the subnets further, creating out of them yet more networks. It was developed, like all forms of subnetting, in response to the shrinking address space in the IEEE private network specifications. If you subnetted your network, in order to create seperate router links you would need to use one subnet per point-to-point link. That’s two addresses used out of potentially hundreds or thousands of addresses in that one subnet. A massive waste of addresses.

VLSM, therefore, allows you to specify one subnet for all of your router links and, upon subnetting it, instead of having hundreds of addresses wasted, you can have hundreds of extra networks, each with only the requisite two addresses. Lets run through an example (the actual point of this post, since I literally am studying into my keyboard. One of the best ways to learn somthing is to teach it to someone else, so that’s what I’m doing). Sit back, ladies and gentlemen, and prepare to be amazed, astounded, and bored to death! Binary, ho!

We start with the Class A private address: 10.0.0.0

It has the default subnet mask of: 255.0.0.0

We require 102 networks, one of which will be dedicated to point-to-point router links

As far as our subnetting is concerned the first octet doesn’t exist, since we can’t change it. Since we can’t change it we don’t worry about it. After that point, everything becomes binary:

255.00000000.00000000.00000000

What, boys and girls, is the subnetting formula? That’s right. 2^{n-2. Two to the power of an unknown and variable number, mnus two, will give us the number of useable networks. So, we need 102 of the little buggers? Well, we can’t do that purely in binary, so we have to go as close as we can, without getting under it. So we work with place-values. 1, 2, 4, 8, 16, so on, so forth. The closest we can get is 128. @8}-2 gives us 128-2, or 126. Good. This fits, so we can work with it. We’re borrowing 8 bits for the root subnet. our subnet mask now looks like:

255.11111111.00000000.00000000

Or

255.255.0.0

If we draw an imaginary line down the seperator between the network portion and the host portion we get:

11111111.11111111|00000000.00000000

So, working from this, we start creating our subnets. Best practice states that, if you have ot have one network purely to be further subnetted for router links, you make it the final network, giving you all that extra room before it to logically scale the network with minimum fuss. So, if we do the first, say, 10 networks, including network address and broadcast, we get the following diagram:


10.00000001|00000000.00000000 First Network
10.00000001|11111111.11111111 First Broadcast
10.00000010|00000000.00000000 Second Network
10.00000010|11111111.11111111 Second Broadcast
10.00000011|00000000.00000000 Third Network
10.00000011|11111111.11111111 Third Broadcast
10.00000100|00000000.00000000 Fourth Network
10.00000100|11111111.11111111 Fourth Broadcast
10.00000101|00000000.00000000 Fifth Network
10.00000101|11111111.11111111 Fifth Broadcast
10.00000110|00000000.00000000 Sixth Network
10.00000110|11111111.11111111 Sixth Broadcast
10.00000111|00000000.00000000 Seventh Network
10.00000111|11111111.11111111 Seventh Broadcast
10.00001000|00000000.00000000 Eighth Network
10.00001000|11111111.11111111 Eighth Broadcast
10.00001001|00000000.00000000 Nineth Network
10.00001001|11111111.11111111 Nineth Broadcast
10.00001010|00000000.00000000 Tenth Network
10.00001010|11111111.11111111 Tenth Broadcast
...
10.11111110|00000000.00000000 Final Network
10.11111110|11111111.11111111 Final Broadcast


Okay. So, our big subnets are worked out, all fine ‘n’ dandy. That’s just plain old subnetting thus far. Now we come to the VLSM. We take our final subnet up there, and subnet it again. We stop thinking, now, of the number of networks we need. Now we think of the number of hosts per subnet. We need 2 hosts per subnet. In order to achieve this we need to borrow 2 bits, as 2² - 2 = 4 - 2 = 2. In order to achieve this we allocate the remainder of the bits, 30 in total, to networks, giving us the subnet mask of:

255.11111111.11111111.11111100

Or

255.255.255.252

Taking this, and acting as if our final subnet there was our root network, we get this (I’ll only do a couple):


10.254.00000000.000001|00
10.254.00000000.000001|11
10.254.00000000.000010|00
10.254.00000000.000010|11


Giving us router links on the networks 10.254.0.4, 10.254.0.8, 10.254.0.12, etc, etc. See the pattern? Going up by 4s. It makes things easier, believe me. That’s all there is to VLSM. It’s exactly like regular subnetting, just using a different address for your root network. Simple, once you know how.

Tomorrow’s the big day. I have to leave here at 7:20 in the AM to catch the train and take a one-hour-and-forty-minute train trip into Frankston Up the Pakenham line to Caulfield, change at Caulfield (technically, all I do is get off the up-Flinders on platform 2 and wait on the same platform for the down-Frankston) and take the next train down to Frankston. To get there and get my exam paid for. Wait for it to activate. Take it. Hopefully get more than 849 out of 1000 for it (minimum pass-mark).

I’m babbling ’bout it. I’m nervous, had you guessed. Wish me luck.

From a post on the Asylum I discovered this wonderful Perl script called Markdown. It takes in plain text like this and turns out XHTML valid markup like this.

From their website:

Markdown is a text-to-HTML conversion tool for web writers. Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML)

It certainly looks most interesting. I intend on testing it… sometime soon. When is a different matter, but, still. Give it a try, if you wish, and drop me a comment letting me know how you go.

Okay. I don’t know what is going on with my new theme, but the comments aren’t showing up in any way, shape or form. Thanks to Dorothea and Alisa for alerting me to this. I’m going to rebuild it from the ground up and see if I can’t get it to work this time around. For now, though, I’m going to switch to the WordPress 1.5 Default theme, and live with it until I can figure it out.

Altough there is still style refinement to be done, and extra template pages to add to cover everything, say hello to Sunday. 3.0. I’m happy with it. Feel free to leave crticisms (constructive ones, of course) in this post’s comment stream, or any suggests for refinements, and I’ll try to address everything as soon as I can.