From jacobson@math-cs.cns.uni.edu Tue Jan 20 13:53:01 2004 Date: Tue, 20 Jan 2004 13:48:59 -0600 (CST) From: Mark Jacobson To: 810-023-01@uni.edu Subject: [810-023-01] Hi Microcomputer Systems students, The chapter one and chapter two review questions will be due on THURSDAY, JANUARY 29th (not on Wednesday, Jan 28th). ---------------------- I got mixed up thinking that this was a MWF class when I did that. Thursday's class: 1. Go over the solution to the group exercise that was started today. I will give you time to try to finish it up, but it will be very helpful if you try to do some of it on your own before Thursday's class. We will go over the solution in class and answer any questions you have, but you will get the most out of the exercise if you familiarize yourself with it on your own between now and the Thursday class. a. Read (or hopefully reread) pages 519-528 of the textbook as you review today's class and try to review and do some more of the group exercise. Pages 524-528 deal with subnetting. b. Read and reread last Thursday's handouts on binary and on subnet masks. The subnet mask UNI currently uses is 255.255.128.0 which means UNI only breaks down into TWO subnetworks. All addresses that have the y octet with a value less than 128 are the first subnet. If the y octet is 128 or higher, it is on the 2nd subnet. Tracing route to iceman.uni.edu [134.161.1.41] Tracing route to henon.cns.uni.edu [134.161.241.4] Tracing route to panther.uni.edu [134.161.1.13] Tracing route to bebop.cns.uni.edu [134.161.241.108] As you can see above, iceman and panther are both on the 1st subnet as the 3rd octet is a value less than 128. The first bit in 1 is off, i.e. is 0, so we are on the first network. And bebop.cns and henon.cns and math-cs.cns all have values of the 3rd octet of 241, which is above 128. The first bit in 241 is on, i.e. is a 1. That means we are on the 2nd network. The two subnet addresses at UNI are: 134.161.0.0 and 134.161.128.0 15 Each of those subnets can have up to 2 host computers, each with its own unique address on that subnet. 15 2 = 2^15 <---- input to bc calculator 32768 <---- output of bc calculator c. Try to do some more and redo the group exercise from today's class, on your own. 2. Talk about chapter one and two basics. Please Do Not Throw Sausage Pizza Away for the 7 layers. 3. Look at an ethereal capture that I did last summer, so we are all looking at the same captured packets. Basics of Binary: Study carefully last Thursday's handout. For binary, if you wanted to see what 134 looked like in binary, there are TWO ways to do it by hand with paper and pencil. Write down the powers of two, up to the largest power of two that is still less than the number you need to convert. Note that 256 is not needed since 134 < 256 128 64 32 16 8 4 2 1 134 -128 Subtract the power of two from your number. --- 6 -4 Subtract the next power of two that is equal to or smaller from --- what is left, i.e. six minus four. 2 -2 Continue the same pattern. --- 0 When you get to zero, you are done. We subtracted 128, 4 and 2 to get 134 "paid off" in base two currency, if you want to think of what it would be like if our money system was based on binary. We would have $1, 2$, 4$, 8$, and 16 dollar bills and so on, right? So the answer is: 128 64 32 16 8 4 2 1 1 0 0 0 0 1 1 0 or 134 = 10000110 10 2 The other way, I will wait to show you on Thursday, with a handout, since it is better suited to paper and pencil than this keyboard and text approach. It involves repeatedly dividing the number by two and writing down both the quotient and the remainder. Note that the remainder is always either 0 or 1 when you divide any number by two. Also, all odd numbers give a remainder of 1. All even numbers give a remainder of 0. Mark P.S. Why it is called base two, i.e. binary, or base 2. 128 64 32 16 8 4 2 1 --- -- -- -- -- -- -- -- 7 6 5 4 3 2 1 0 2 2 2 2 2 2 2 2 <----- base 2 --- -- -- -- -- -- -- -- 128 64 32 16 8 4 2 1 2 to the 8th = 256 2 to the 9th = 512 2 to the 10th = 1024 = 1K = 1 kilobyte or about 1 thousand 2 2 to the 20th = 1024 = 1M = 1 megabyte or about 1 million 3 2 to the 30th = 1024 = 1G = 1 gigabyte or about 1 billion