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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 topicsIPv4
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? 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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