| CS70
Network Fundamentals & Architecture
David
Morgan |
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AdministrativaReading
list, per chapter:
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FALL
2020 This Website (http://classpage.dmorgan.us/) will be used extensively to communicate with you. Announcements, grade reports, and assignments will be posted here. Please access the website from any SMC computer lab. Alternatively, it can be viewed from an internet-connected browser anywhere. You are responsible for awareness of the information posted here. Announcements/grades/current topicsdns-exercise-howto - recorded video in which I go through the dns homework exercise. (12/3) Homework Second test - our final class meeting will be next Thursday 12/10. The SMC College District Calendar shows a final exam period December 15-22. We will have an online, non-cumulative Test2 on current topics, similar to our recent Test1 on the earlier topics. It will be on Thursday 12/17. (12/3) Important name service files on linux
computers - Addresses, functions - you know them. Don't get them mixed up.
(12/3) Grades - have been updated, link entitled "Grade information" at left. They include the tcp-interactvie assignment the focuses on tcp protocol's sequence and acknowledgement numbers the count off bytes that have been sent from one side to the other.. Please call any anomalies to my attention. (11/28) Office hours meeting for any interested students, will be by Zoom Saturday, November 28, 1pm. No agenda, we can talk about anything you care to raise. (11/20) No class next Thursday Nobember 26. SMC observes Thanksgiving holiday. (11/19) Grades - have been updated, link entitled "Grade information" at left. They include the xinetd "super server" assignment. Please call any anomalies to my attention. (11/19) Homework Letter-upgrader variants - They bestow a protocol on the otherwise protocol-less original letter upgrader pair. The original client sends a letter to the original server, which robotically and single-mindedly sends the next letter of the alphabet back. The new versions allow either the next, or possibly instead the previous, letter to be returned. The client now has to tell the server which, and the server has to differentially respond accordingly. That's a protocol. (11/19) Various services and the server programs and protocols they use.
*batp - bidirectional alphabet traversal protocol ? (11/19) Homework Remaining calendar - beyond tonight there class
meetings on 3 upcoming Thursdays: TCP (and UDP) Ports you should know Manufacture
of first 4 nodes of the internet - Computers from different
manufacturers could never communicate. By a deliberate indirect
means, the internet enabled them to do that. The particular makes and models of the
original four computers knit together in the original
"Internet" were: Interesting video - fiber optics and undersea cabling 20.000 cables under the sea. (11/8) Test - will be on Canvas under "Quizzes," available during this coming weekend (midnight Friday night till midnight Sunday night). It allows 1 hour 45 minutes for you to take it, from the time you begin. (11/5) Alternative internetworks - here are 3 variations on the theme of our "internetworking" assignment's topology. And here is an extended version of the "linear" internetwork that featured in our "internetworks" slides. There are some questions based on both these images and their topologies on the upcoming test. (11/5) Grades - have been updated, link entitled "Grade information" at left. They include the internetworking assignment. That assignment is heavily weighted (important, high "learning density") so if you have not done it and would like to complete it please do so. Please call any anomalies to my attention. (11/5) Test - will be on Canvas in the coming week, available during a 2-day span to be discussed and decided upon in class tonight. No homework this week. (10/29) Grades - have been updated, link entitled "Grade information" at left. They include the macip assignment. Please call any anomalies to my attention. (10/29) Grades - have been updated, link entitled "Grade information" at left. They include the error detection assignment. Please call any anomalies to my attention. (10/22)
Homework - Grades - have been updated, link entitled "Grade information" at left. They include the "IP packet delivery" assignment, featuring Sally and Harry. Please call any anomalies to my attention. (10/15)
Homework -
Upcoming homework - preview it if you wish, will be
assigned next week A real-world DSL order - We have been emphasizing what a "network" is in technical, mathematical terms. It's a range of numbers that people express by telling other people what the first number in the range is (network address), and how many numbers there are in it (netmask). This surfaces in the commnuique I received once when I ordered a subnet from an ISP. Please see the links in the column at left under the heading "Real world DSL." Read the analysis. (10/15) Who was IANA? What about now? Where are they? What is their job? (10/15) Grades - have been updated, link entitled "Grade information" at left. The current "subnet partitioning" assignment is not due till the end of the day. For those who have already turned it in, I graded it and posted those assignment grades. However they have not yet been incorporated into the overall cumulative average grades. Also new are the individual grades I have entered or changed in response to email communication with some of you in the past week. Please check your grades and let me know of any anomalies. (10/8) Golden rules for deciding how to ship a packet (Fore Systems "IP packet delivery"):
We reviewed the concept behind the "IP packet delivery": if IP thinks a destination IP address is local it arps for that IP address, if not it arps for the IP address of its default router (which comes from the routing table). Everything hinges on what "local" means. That is a function of the given destination address, the local address, and the local netmask. Network calculators and/or the linux "ipcalc" command can help you recreate IP's "thinking process" in this regard for particular subnets, addresses, and netmasks. A related description of the thinking process comes from our textbook, Computer Networks and Internets, Douglas Comer (see p. 368 fifth edition). (10/8)
Homework - packet-delivery-harry.jpg (or alternatively use
.png instead of .jpg filename extensions) and upload them to your
assignments directory on the server. Don't use any other format. due
on server by end-of-day Wednesday October 14 Opportunity - NASA Community College Aerospace Scholars (10/8) Home network map - because sometimes in class I refer to my home network for illustration of certain points, I've made a diagram of it. (10/3)
Homework - Double match?? - what would happen if an IP packet's destination address matched two entries in the routing table. To which of the two interfaces would it be sent? Is this even possible? (10/1) Packet capture files for you from the "wireshark"
in-class exercise The IP addresses of the machines I used were 192.168.1.10 and 192.168.1.12.
Those are reflected in the captures. Get
the files (unzip) then open them in Wireshark. You can then ponder the questions the exercise asks and use the captures to help
you understand. The files are: Satisfy yourself you have a pretty good idea what you are looking at. In particular, compare the header structures you see in the captured frames with the ones mapped out in the TCP/IP Pocket Reference Guide. And, practice using Wireshark's "Follow TCP stream" feature, found by right-clicking on packets in the packet list pane. It will starkly and unmistakably extract the password used in the telnet login session. And it will reveal the content of the web page obtained in the http browse session. There is nothing to turn in. (10/1) Grades - have been posted, link entitled "Grade information" at left. Grades include the upload of "introduction.txt" (or any other file) and upload of the wireshark capture screen printout. Please check your grades and let me know of any anomalies. (9/23) Network Address + Netmask
= Subnet It is the network address that establishes the position or starting point of the address range or block that is the network. And it is the netmask that establishes its extent or size. As an example consider a network whose network address is 64.52.25.224 and whose netmask is 255.255.255.224 (the one that signifies "thirty-two" as size). The number line below is a microscopic segment of the number line for the whole internet. That number line is 4 billion addresses in length (because with 32 bits 4 billion is the number of distinct address values that can be composed). Here, with the first 24 bits of our address (64.52.25) we are narrowing in on a particular little 256-address segment within that number line. Within the segment, the network address further positions us with final precision. This idea of sectioning off the 4 billion addresses into separately addressable subordinate pieces is called subnetting, and the resulting pieces or address groups are called subnets. 64.52.25.224/255.255.255.224:
A short accompanying, explanatory recorded explanation of performing subnetting. (9/24)
Homework -
Routing - important formulations of
the "route" command Add route to a machine (host route): Study these commands intently and try to internalize the semantic meaning they embody. (9/24) Windows route command - differs in syntax and scope somewhat from the linux command of the same name. But it is kindred in spirit and operates on the very same internet protocol (though not the same coded implementation of it). The internet protocol is defined outside Microsoft and outside linux. Both Microsoft and linux programmers have taken their hand to writing programs that do what the protocol defines. Including a "route" command to manipulate the protocol's route table. In Windows, open a command box and execute "route print" if you wish to see the route table. (9/24) Network size for common netmasks:
(9/24) Lego project - make a router for your toy trains. (How is this an applicable analogy to the processing of frames within a computer router?) (9/24) Wireshark, protocols, and people
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Homework - Undersea cabling - former
student Philip Postovoit did the service of researching cabling quite
thoroughly. Of the many links
about it he sent me, I found particularly interesting: What other data link protocols
besides ethernet are out there? You might instead have
What's the difference? Homework update - green light
for homework in 9/10 posting below statistics-udp.jpg (or .png) I ask you to place these into a zip file named "wireshark-homework.zip" and upload it to your assignments directory. (Please ignore the questions you will see at the bottom of the assignment page. They are not for you. I only want the screenshots.) Please start this assignment before Thursday's class. At class I will spend a little time making sure the assignment and steps to perform it are understood. We will also decide a due date then. due on sputnik in the "assignments" subdirectory of your home directory end-of-day Friday, September 25 (9/15) Homework VM files on Google Drive - I have asked students to download some files from OneDrive. Some of you have not yet done so or encountered problems in doing so that we have not solved. I have placed a second copy of the files elsewhere, namely on Google Drive. I have also emailed you an access link today. Please copy it into a browser. It should take you directly to a screen offering you the files. If you have not yet obtained the files from OneDrive as originally instructed, please try to get them from Google Drive now instead. (9/10) RFC process - how protocols get created. Here is a current example, HTTP 2 which was published as an RFC in May, 2015. See in particular the development timeline that has led it to this point. (9/10) Screenshot of Microsoft Network Monitor. Compare the interface with Wireshark's. It demonstrates the product category (network "sniffers") to which both products belong.
Link to tonight's class (This is
hosted at my home. I don't know if upload speed will be a problem
for you to listen to the recording. Let me know if so please.) (9/3) Course outline - with approximate weekly topic coverage corresponded to related readings, homework assignments, and in-class slides I will use. Please follow this outline as we move through the topics, for assignments and reading I want to assign.
Homework - A virtual machine (VM) for you
- hands-on lab exercises will be performed on a virtual machine that
you can run in your own computer. A Remote Unix system account is available for your use. Internships - a link I have been asked to publicize to students. (8/30) Using ssh (secure shell). ssh is an important tool you will use for interacting with remote computers. For that you will need an ssh client. There are a number of ssh client alternatives. Distributing files from sputnik to the class as a whole, publicly - the above file transfer discussion describes file movement to and from your own home directory, exclusive to you. Sometimes I will want to have someplace to put a file so everybody can get to it and download it. When I do that, here's how to download them. Cover art on Tannenbaum textbook:
What is it?? "Number please?" asks the switchboard operator. The switchboard is a board. It's for switching. Switching changes a circuit between you and somebody. It can complete a circuit to your Aunt Bheulah in Iowa City so you can thank her for the knit socks. After you hang up if you want to call your uncle in Waco you'll need to switch circuits, to get a circuit to him instead of her. That's what the operator does for you. The "switch"ing in "switch"board is circuit switching. Nowadays in computer networks it's not circuit switching anymore, it's packet switching.
Functional layering - the famous "Open Systems Interconnect" model is depicted below. Somebody once had the idea that maybe there could be a way to get independent computer systems of different types to be able to exchange information with one another. The diagram blueprints the idea for "how in the world are we going to make that work??" That idea is the subject of this course.
First-day administrative information you will need to know: Slides available online - for most if not all slides I will show in class. Links to them can be found in the "Slides" column of the course outline. Course-long textbook reading - a chapter-by-chapter list ( 6th edition, 5th edition ). The textbook is divided into chapters and they in turn into numbered sections. The list tells you which sections to read for this course when chapters are assigned. For example if I assigned chapter 10 and it had 17 sections, if this list specifies "10.1-100.5, 10.7, 10.12-17" it means I didn't feel sections 10.6 nor 10.8-11 were relevant enough so I only list the balance of the chapter. Read unlisted portions for your own interest if you wish, but the listed sections are what's officially assigned to you. Textbook - Computer Networks and Internets, sixth edition, Douglas Comer, Pearson Prentice Hall , 2015. Wireshark - is an excellent free packet capture utility.
What is a packet, and why caputre it? We'll talk about that later. I
will ask you to install and use Wireshark later in the semester,
assuming you have a linux or windows computer available on which to
do so. Please visit Wireshark's
home page. |
"What
hath God wrought?"
"Mr.
Watson come here, I want to see you."
"lo"
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