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Administrativa
Reading
list, per chapter:
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FALL
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 topicsGrades - have been updated, link entitled "Grade information" at left. They include the tcp interactive telnet assignment. These grades cover the full set of assignments for the semester plus the first test. Please check your grades and let me know of any anomalies. (12/20) Test reschedule - per your request during class last night. The test will be available throughout the two day period Sunday 12/19 and Monday 12/20. It is a 2-hour test, closing 2 hours after you start it. Take it any time at your convenience, on one of those two days. (You shouldn't start after 10:00pm Monday, as you will be cut off at midnight and not have a full 2 hours.) (12/10) Images 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 and during the test. (12/9)
Second test - our final class meeting will be tonight Thursday 12/9. The SMC College District Calendar shows a final exam period December 14-21. We will have an online, non-cumulative Test2 on current topics, similar to our recent Test1 on the earlier topics. (12/9) Important name service files on linux
computers - Grades - have been updated, link entitled "Grade information" at left. They include the "reconnect to internet" exercise. Please check your grades and let me know of any anomalies. (12/8)) Class question answered - you asked a question about udp in class last Thursday. It refers to the 2nd slide in
this presentation. Although the slide addresses tcp, "udp" could
just as well replace that in the labeling and remain accurate. Homework - per this posting below, we didn't have time to
show this during class so please listen to it. No class Thursday Nobember 25. SMC observes Thanksgiving holiday. (11/23) Remaining calendar - beyond today there are 2
upcoming Thursday class
meetings:
and also do - the exercise at course outline section 7's link entitled "connect a classroom to the internet." This goes back to the network layer. due on sputnik by end of day Monday December 6. (11/24)
and also do - the exercise at course outline section 11's link entitled "tcp interactive dataflow tracking." due on sputnik by end of day Monday December 13 (11/24) Homework
- for the remainder of the semester, timing at your
convenience Addresses, functions - you know them. Don't get them mixed up.
(11/19)
Class schedule and ICANN recording - a link to last night's talk by David Huberman can be found on the "Zoom meeting recordings" page. I had intended to convene class following his talk, when we had an hour of scheduled time remaining. I wanted to make some review comments on questions in the recent test. It was inopportune to do so. I plan to record my comments on the test and ask you to listen later. Next Thursday is Thanksgiving and we do not meet. I will also publish further homework to occupy you between now and our next meeting December 2. (11/19) Grades - have been updated, link entitled "Grade information" at left. They include the BIND/dns name service exercise plus the test. (Grades for a few individual cases may not yet be included.) To help interpret the test grade, please see this general explanation. Please check your grades and let me know of any anomalies. (11/16) ICANN talk on Thursday - it was asking a lot for you to do the BIND/dns assignment at the same time as the test. But as a result of the exercise I think you have enough grasp of what name service is and how it works to let you follow a further conversation about it, which is what we expect from ICANN's David Huberman on Thursday. I think he's going to talk about ways and means of 1) encrypting and/or 2) authenticating dns traffic. This will involve the public-key cryptography concepts I tried to introduce in the supporting video (link below). The specific technologies he talks about might include RPKI and BGP, DoH (dns over https), dns over tls, DNSSEC, possibly others. If you wish, search for those and read a description of each. (11/16) Supporting video - for the upcoming ICANN talk. I discuss public-key cryptography, digital signatures, and certificates. They are related to each other. I offer them because I think they are also related to the kinds of topics I understand ICANN to be presenting to us on Thursday. (11/12) Homework
- I may locate and recommend to you
other resources between now and November 18. I may offer an
(optional) office hours meeting following the assignment due date
(since by then you are going to be dns-intelligent, beyond even your
usual level) and before the November 18 talk. Test - is published on Canvas. It will be available Sunday and Monday, November 14 and 15. 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.) (11/4) Grades - have been updated, link entitled "Grade information" at left. They include the xinetd/chomper and internetworking assignments. They do not yet include the internetworking assignment. Please check your grades and let me know of any anomalies. (11/5) No class meeting next week - November 11, SMC observes Veteran's Day. (11/4) Homework Deferred in favor of DNS - please see 11/6 Homework posting above (11/4) 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: 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. (10/28) Various services and the server programs and protocols they use.
*batp - bidirectional alphabet traversal protocol ? (10/28) 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. (10/28) Test - for the upcoming test (see 10/21 posting below), here are some questions for you to consider. See also the links under the heading "Reading list, per chapter" in the column at left. That list designates the portions of the textbook whose content can be covered in the test. (10/28) Homework Student participation lab tomorrow - I'd like to do a joint, guided exercise in class tomorrow night. I will perform it while you can follow along and do it yourself. It requires two VirtualBox VMs, so you should prepare by having VirtualBox available. I will use the same pair of machines that was created for our earlier Wireshark exercise (CLIENT and SERVER). If you have not deleted those, they will do nicely. Or, it's easy to make two fresh clones of the base machine for this purpose. Grades - have been updated, link entitled "Grade information" at left. They include the error detection asssignment. Please check your grades and let me know of any anomalies. (10/27) Linux virtual terminals in VirtualBox VMs - in linux you can normally switch from one virtual terminal to another with the simultaneous triple keystroke combination of Ctrl, plus Alt, plus the function key having the number of the virtual terminal you want. If you wanted virtual terminal 5 it would be ctrl-alt-F5 for example. But that doesn't work in VirtualBox, as I encountered in class last night. However it does work if I replace ctrl-alt with the right Ctrl key, or either Alt key. If you wanted virtual terminal 5 it would be Alt-F5 for example. Experiment with it. It's a useful trick. (10/22) Dropped students - I dropped non-participating students. That's reversible, but of questionable advisability this late in the semester, upon request. If you think completing the course is not infeasible for you please tell me about it and request a reinstate code. (10/22) Homework - 1972 explanation of the Arpanet - the ARPA (Advanced Research Projects Agency) network which became the Internet. Listen to it optionally. I came upon it 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. (10/21) Grades - have been updated, link entitled "Grade information" at left. They include the MAC-vs-IP-addresses asssignment. Please check your grades and let me know of any anomalies. (10/21) Test - it will be time for a test once you have performed the internetworking homework exercise, which is due October 31.. So the test looks likely to fall in roughly the first week of November. I will talk more about the test contents 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. (10/21) IPv4
Address Depletion - listen to these 2009-10 perspectives Grades - have been published, at the link entitled "Grade reports" at left. They include the packet delivery ("Sally and Harry") assignment. Please call any anomalies to my attention. (10/14)
Homework - A real-world order for IP addresses from an ISP - 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. (10/14) Who was IANA?
What about now? Where
are they? What is their job?
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 13 Grades - have been published, at the link entitled "Grade reports" at left. They include the subnet partitioning assignment. Please call any anomalies to my attention. Soon I would like to drop those students who have submitted no work. (10/7) 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). (10/7) Grades - have been published, at the link entitled "Grade reports" at left. They include the "netmask legality" assignment. Please look yourself up by the same anonymous 5-digit value you derived in calculating your sputnik remote server password. Please call any anomalies to my attention. Soon I would like to drop those students who have submitted no work. (10/4)
Homework - Grades - I will defer posting grades (and grading) until Monday. The netmask legality assignment was due but you did not have benefit of last week's related lecture until last night. So please take additional time if you need it, finish and uploading that assignment by Monday. (The grades shown currently are those that I posted last week. Individual changes I made since are not yet reflected.) (9/30) 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? (Hint: it's called "longest prefix match." Longest prefix equates to smallest network. You can look it up.) (9/30) 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. (9/30) Packet encapsulation clarification - one of the slide presentations we viewed about ethernet has provoked questions. 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. 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. (9/30) Grades - have been published, at the link entitled "Grade reports" at left. They include the "ethernet frames" assignment. (The majority of student haven't done it.) Please look yourself up by the same anonymous 5-digit value you derived in calculating your sputnik remote server password. Students are free and independent and I expect you to be aware of the grade you are earning, in particular your cumulative average, and that each student's grade will be that of his or her conscious choice. Please call any anomalies to my attention. (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. (9/23)
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. (9/23) 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. (9/23) Small networks: sizes for some common netmasks:
(9/23) Lego project - make a router for your toy trains. (How is this an applicable analogy to the processing of frames within a computer router?) (9/23) Wireshark, protocols, and people
- 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:
(9/16) What other data link protocols
besides ethernet are out there? You might instead have
What's the difference? 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. (10/21) Norm Abramson 4/1/1932 - 12/1/2020
(9/16) Grades - have been published, at the link entitled "Grade reports" at left. They include the "exercising wireshark" assignment in addition to the initial wireshark screenshot upload. There is a cumulative (weighted) average of these two. The cumulative average will be maintained to incorporate future work, assignment by assignment as they are completed, over the semester. Please look yourself up by the same anonymous 5-digit value you derived in calculating your sputnik remote server password. Please call any anomalies to my attention. (9/16) Grades - have been published, at the link entitled "Grade reports" at left. Please look yourself up by the same anonymous 5-digit value you derived in calculating your sputnik remote server password. Please call any anomalies to my attention. (9/13) By popular demand - at least 2 students in class tonight expressed interest in this bash cheat sheet (summary by a former student of things you can do using the command line in linux or mac). (9/9) Green light - go ahead and download the vmconfigure scripts for your platform ("bash" version for linux/apple, "batch" version for Windows). In class tonight I had asked you to wait till I could test and confirm them. I did. They are OK. They serve to set up machines for your wireshark homework, below. (9/9) 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 Wednesday, September 15 (9/9) 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. (9/9) Screenshot of Microsoft Network Monitor. Compare the interface with Wireshark's. It demonstrates the product category (network "sniffers") to which both products belong.
(Network Monitor comes with the Server editions of Windows and won't be found in our consumer editions.) (9/9) Remote server access how-to video. Several programs that provide login connection to a remote server, file transfer connection, or both, are discussed and demonstrated. These are the tools for accessing sputnik.smc.edu. (9/3)
Homework - Opportunity - ICANN (Internet Corporation for Assigned Names and Numbers) "Shaping the Future of the Internet: ICANN's Newcomer Programs" (8/30) Opportunity - NASA community college aerospace scholars program (8/30) 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. Dates and deadlines 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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