| CS70
Network Fundamentals & Architecture
David
Morgan |
Our curious network: Not any Damsel, which her vaunteth
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Administrativa
Reading
list, per chapter:
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SPRING
2021 This Website (http://classpage.dmorgan.us/) will be used extensively to communicate with you. Announcements, grade reports, and assignments will be posted here. You are responsible for awareness of the information posted here. Announcements/grades/current topicsImages from/for the test - Canvas does not display some images if you use browsers that are not "up to date." A few of my questions do contain images. Depending on your browser you might not be able to see them. In case that happens to you during the test, I have made the images alternatively available here. You are free to look at them in advance of the test. (6/12) Other courses I teach - are known to you from the main website front page. There, you can see the class-specific pages from recent semesters for a concrete idea of their exact content (particularly see the course outlines). CS40 - Operating Systems (3hr credit, next offering Fall 2021) CS41 - Linux Workstation Administration (3hr credit, next offering Summer 2021) CS75 - Network Protocols further depth and variety on the topic beyond CS70 (unscheduled) CS78 - Secure Server Installation & Administration (unscheduled) (6/5). Posted - a new slide presentation about the dhcp protocol. The new link is in course outline section 14, entitled "dhcp". We will talk about dhcp, as well as apache, today. (6/5) Second test - The SMC College District Calendar shows a final exam period June 8-15. We will have an online, non-cumulative Test2 on current topics, similar to our recent Test1 on the earlier topics. It will be on Saturday 6/12. I plan to schedule it within our regular class period that morning, from 10am till noon. It will be on Canvas, and I plan to be there in chat in real time, in case you want to ask any questions. (6/5) Grades - have not been updated since last week, link entitled "Grade information" at left. The dns assignment is yet to be graded. I will grade it shortly. Please call any other anomalies to my attention. (6/5) Grades - have been updated, link entitled "Grade information" at left. They include the "connect classroom to internet" homework. Please check your grades and let me know of any anomalies. (5/29) Second test - our final class meeting will be next Saturday 6/5. The SMC College District Calendar shows a final exam period June 8-15. We will have an online, non-cumulative Test2 on current topics, similar to our recent Test1 on the earlier topics. It will be on Saturday 6/12. I plan to schedule it within our regular class period that morning. (5/29) Homework
- Grades - have been updated, link entitled "Grade information" at left. They include the tcp interactive dataflow homework. Please check your grades and let me know of any anomalies. (5/21) Important name service files on linux
computers - Addresses, functions - you know them. Don't get them mixed up.
(5/21) Homework
- Remaining calendar - beyond today there class
meetings on 3 upcoming Saturdays: Grades - have been updated, link entitled "Grade information" at left. They include the xinetd "server manager" homework. Please check your grades and let me know of any anomalies. (5/15) Grades - have been updated, link entitled "Grade information" at left. They include the test. Please check your grades and let me know of any anomalies. (5/8) 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 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. (5/8) Various services and the server programs and protocols they use.
*batp - bidirectional alphabet traversal protocol ? (5/8) Test - is published on Canvas. It will be available Sunday and Monday, May 2 and 3. It is timed, allowing 105 minutes from the time it is started. Take it any time Sunday or Monday. (You shouldn't start after 10:15pm Monday, as you will be cut off at midnight and not have a full 105 minutes.) (5/1) Homework Grades - have been updated, link entitled "Grade information" at left. They include the internetworking assignment. Please check your grades and let me know of any anomalies. (4/24) Homework 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: 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. (4/23) Test - for the upcoming test (see 4/3 posting below), here are some questions for you to consider. (4/15) No class April 17, due to spring break. (4/10) Homework - Grades - have been updated, link entitled "Grade information" at left. They include the macip and error detection assignments. Please check your grades and let me know of any anomalies. (4/10) 1972 explanation of the Arpanet - the ARPA (Advanced Research Projects Agency) network which became the Internet. Listen to it optionally. I came upon it today and found it very interesting. See if you can grade these internet inventors on the accuracy of their predictions about the potential of their network. (4/4) Grades - have been updated, link entitled "Grade information" at left. They include the "IP packet delivery" assignment featuring Sally and Harry. Please check your grades and let me know of any anomalies. (4/3) Test - it will be time for a test once you have performed the internetworking homework exercise, which looks likely to be finished/due around April 20. So the test looks likely to fall somewhere in the April 20-30 time period. I will talk more about it in class before the test date. See the notations in the "Reading list, per chapter" (left-hand column of this page) indicating which portions of the textbook can be covered in the test. (4/3) Spring break - is the week of April 12 per the SMC calendar. As affects us, we will meet as usual next Saturday 4/10 but not the Saturday thereafter 4/17. We will resume meeting Saturday 4/24, plus the next 6 Saturdays after that before we reach final exam week and course end. (4/3)
Homework - 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. (4/3) Who was IANA?
What about now? Where
are they? What is their job? Grades - have been updated, link entitled "Grade information" at left. They include the "subnet partitioning" assignment. Please check your grades and let me know of any anomalies. (3/27) 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). (3/27)
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 Thursdsday April 1 Grades - have been published, link entitled "Grade information" at left. They include the "netmask legality" exercise.. Please call any anomalies to my attention. (3/20) 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. (3/20)
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? (3/20) 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. (3/20) Monday evening office hours - we will hold an office hours zoom meeting at 7pm tonight. The purpose is to address anything you like related to the mechanics of the VirtualBox VMs or the homework assignments we have been doing or the concepts we have been discussing. Use the same Zoom credentials that you do usually for regular Saurday class meetings. (3/15) Packet encapsulation clarification - one of the slide presentations we viewed about ethernet provoked questions during lecture two weeks ago. It was about the relationship in a frame among the various protocols that appear within it. The word is "encapsulation." Think Russian dolls. Think one-inside-the-other. Please revisit the slide presentation and view the two slides shown on its page 8. The first one shows the general concept, better than it did before. The second one shows a real-world frame from a Wireshark capture, and breaks its content down into the protocol components within it. This real-world frame is one that was captured while performing the Wireshark sniffing homework making a telnet connection. (3/15) Packet traffic composition - some of it is nugget, some is dross. Some of it is kernel, some is chaff. "...traffic is composed of user and app oriented information [nugget] augmented by protocol information inserted for the benefit of network operation [chaff]." When we communicate information, why do we carry a lot of deadweight extra information around with it? When we mail paper letters, why do we send a lot of extra envelope paper along with it? For benefit of the delivery operation. (3/15) Norm Abramson 4/1/1932 - 12/1/2020
(3/13)+ 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. (3/13) >>Partial homework answer<<
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. (3/13) 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. (3/13) Small networks: sizes for some common netmasks:
(3/13) Lego project - make a router for your toy trains. (How is this an applicable analogy to the processing of frames within a computer router?) (3/13) Wireshark, protocols, and people
- Grades - have been published, link entitled "Grade information" at left. They include the "ethernet frames," exercise plus 3 students' wireshark sniffing exercises submitted in the last couple of days.. Please call any anomalies to my attention. (3/12) Grades - have been published, link entitled "Grade information" at left. They include the wireshark sniffing exercise. Please call any anomalies to my attention. (3/10) Grades - have been published, link entitled "Grade information" at left. They include only the initial wireshark screenshot assignment. Please call any anomalies to my attention. (3/6)
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:
(3/6) What other data link protocols
besides ethernet are out there? You might instead have
What's the difference? Sunday office hours - we will hold an office hours zoom meeting at 3pm tomorrow Sunday, February 28. The main purpose will be to get students' VirtualBox installations and virtual machine importations done successfully. It's optional. It will be for students in both my CS40 and CS70 classes. Therefore this will be a different Zoom meeting than usual, and you won't join it the same way you join your class. Rather, please use this link instead: https://cccconfer.zoom.us/j/98868349116?pwd=alc4alZ0Yy91TjBxOFhOQ2hFajlPdz09 Homework 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.) due on sputnik in the "assignments" subdirectory of your home directory end-of-day Tuesday, March 9 (2/27) 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. (2/27) Screenshot of Microsoft Network Monitor. Compare the interface with Wireshark's. It demonstrates the product category (network "sniffers") to which both products belong.
(2/27) Dates and deadlines - I can be a little more specific than
I was in class: NASA Perseverence Mars rover landing last Thursday. NASA YouTube channel. Operating systems used by mission components: according to email message from JPL's Dj Byrne. (2/20)
Homework - Course outline - with rough 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. 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. 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.
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"What
hath God wrought?"
"Mr.
Watson come here, I want to see you."
"lo"
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