Xaero.org

So I’m neck deep in my GRE studies. I’ve already gone through two GRE books and an ebook. I’m close to finishing my third book (this test is NOT easy). I’m learning some interesting properties of numbers such as the following:

Integers:

• Integers are whole numbers (whether positive or negative)
• Fractions are not integers
• Zero is an integer!
• Positive integers get larger as they move farther from zero
• Negative integers get smaller as they move farther from zero

Consecutive numbers:

• Listed in order of increasing value without any numbers missing between them
• Fractions and decimals cannot be consecutive numbers; only integers can!
• You can even have consecutive even integers: 2, 4, 6, 8…

Properties of Zero:

• 0 is even
• 0 plus any other number is equal to that number
• 0 multiplied by any other number is equal to 0.

Positives and Negatives:

• pos x pos = pos
• neg x neg = pos (“two wrongs make a right” is my memorization tool)
• pos x neg = neg

Even or odd?

• Any number that can be cleanly divided by 2 is even (i.e. no remainder)
• Any number that cannot be cleanly divided by 2 is odd (i.e. has a remainder)
• Zero is even
• Fractions are neither even nor odd
• Any integer is even if its units digit is even, and odd if its units digit is odd
• Multiplying and adding odd and even integers
• even x even = even
• odd x odd = odd
• even x odd = even
• even + even = even
• odd + odd = even
• even + odd = odd

Absolute Value:

• Absolute value is how far away a number is from zero
• Absolute value is always a positive integer whether or not the number in question is positive or not

Prime Numbers:

• A number is prime when it is only divisible by itself and the number 1
• Here’s all the prime numbers less than 30: 2,3,5,7,11,13,17,19,23,29
• Zero is not a prime number
• 1 is not a prime number
• 2 is the only even prime number
• Prime numbers are always positive integers. There’s no such thing as a negative prime number

Rules of Divisibility:

• An integer is divisible by 2 if its units digit is divisible by 2. For example, 598,447,896 is divisible by 2 because the units digit (6) is divisible by 2.
• An integer is divisible by 3 if the sum of its digits is divisible by 3. For example, 2,145 is divisible by 3 because (2+1+4+5 = 12) is divisible by 3.
• An integer is divisible by 4 if its last 2 digits form a number that’s divisible by 4. For example, 712 is divisible by 4 because 12 is divisible by 4.
• An integer is divisible by 5 if its units digit is either 0 or 5
• An integer is divisible by 6 if it’s divisible by both 2 and 3
• An integer is divisible by 9 if the sum of its digits is divisible by 9
• An integer is divisible by 10 if its units digit is 0

Remainders:

• When one integer cannot be divided evenly by another, the remainder is what is left over after the division
• When one integer divides evenly by another the remainder is zero (no remainder)

Factors:

• A number is a factor of another number if the second number can be divided by the first with no remainder
• Factors of 12: 1,2,3,4,6,12
• Best to write factors in pairs to make sure you get them all:
• 1 and 12
• 2 and 6
• 3 and 4

Multiples:

• A multiple of a number is that number multiplied by an integer
• Multiples of 10: -20 (10 x -2), -10 (10 x -1), 10 (10 x 1), 20 (10 x 2), etc…

There’s obviously far more to the GRE than these simple concepts but some are quite handy and will make short work of doing calculations for the GRE. Yea, you can’t use a calculator at all. Fire up those neurons!

I SSH between my many computers several times in the course of a day. Today when I went to SSH to my web server I couldn’t quite figure out what was wrong. I could ping the IP address but SSH just didn’t want to work. I tried restarting the SSH daemon and when that didn’t work, I rebooted the entire box. After it still didn’t work, it finally hit me: I forgot to renew my domain name and it was set to expire on July 17th! To confirm, I did a simple dig lookup:

; <<>> DiG 9.4.2-P2 <<>> xaero.org
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46405
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Jul 20 13:08:14 2009
;; MSG SIZE  rcvd: 124

Oops!! Needless to say, I very quickly renewed my domain name and within a few short hours my nameservers were happily serving up DNS again. Thankfully my registrar provides a grace period for renewing expired domains so they don’t immediately get thrown back into the available pot. Next time I’ll stamp a sticky note on my forehead.

W00-h00! Finally passed the last test. I took it a few months ago and failed pretty badly.  This time around I continually reviewed my material to make sure I knew it cold. I’m glad I’m through with this certification. I may move towards the design track. But first, a much needed break.

Been experimenting with some fun stuff on the site, as you may or may not have noticed. First I’ve enabled comments, but you have to solve a CAPTCHA. Instead of a normal CAPTCHA though, I’m using a reCAPTCHA. The difference is pretty cool though. Instead of just solving a bunch of jumbled letters, you’re actually helping to digitize books by “reading” words that OCR software couldn’t solve. Pretty cool! Secondly, I’ve made my permalinks a little prettier. I’m considering changing my domain name too. Now that you can comment, let me know if you like this domain or www.xaero.org!

So I finally sat down and added something to the Articles section. Check it out!

So I passed another CCNP exam today! Three down, one left to go. This one was far easier than the routing and switching exams. The shear amount of content those exams had was, in a word, overwhelming. I wonder if it’s intended to weed out the slackers so only the truly dedicated persevere. The BCRAN tests your knowledge of a variety of different remote access technologies, from ISDN BRI/PRI (yes it’s still around), to Frame Relay (yes, it’s still around), to DSL, Cable Modem, and Satellite. You’re required to learn and apply backup strategies so if your main link dies or becomes saturated, you have a means to back it up. You have to know the intricacies of several different queuing and compression strategies so you can optimize WAN capacity. Finally, you have to learn several ways of securing remote access, using such things as AAA and IPSec. Since this exam is retired, you have to be a Networking Academy student to take it, however, it still counts towards a CCNP. All in all, a fairly difficult exam, but certainly passable with the right amount of study and hands-on time. Onward to the last exam, the CIT!

Wow, did a speed check on my Internet connection at www.speedtest.net and got some surprising results:

Check it out

So, I finally passed another CCNP test! I actually took this test back in September and failed it by just a few questions. I’ve been extremely busy with other stuff since then, but found time here and there to study and fill in my knowledge gaps. The book that pushed me over the passing edge is none other than Routing TCP/IP, Volume I. I felt that this test was very difficult (I did fail it the first time after all). You’re expected to know 7 routing protocols faily intimately, subnetting, VLSM, controlling routing updates, redistribution, and on. It seemed like once I finished learning the last routing protocol, I forgot the first one. Jeff Doyle’s book certainly helped since it put everything into perspective and was very approachable. Highly recommended, even if you just use it as a desk reference. Well, onward to BCRAN and CIT!

Yes, I realize that the BCRAN and CIT are expired, but I’m a Cisco Networking Academy student and am able to take them through the end of this year.

Handy little guide to the people behind what is the Internet today:

http://www.simonsays.com/titles/0684812010/pioneers.html

Boy if this doesn’t somewhat show my age. Here’s a spoof that Engadget did of a BBS set back to 1985. For all the n00bs, a BBS is a Bulletin Board System, or a Blog/Message Board/File Sharing thingie that you dialed into with your 2400 (if you lived on the cutting edge) baud modem. Articles are included on the latest and greatest tech goodies of the day. We sure have come a long way. Enjoy it here.