The picture

CS70 Network Fundamentals & Architecture


David Morgan
Santa Monica College
see syllabus for email address
Our curious network:
Not any Damsel, which her vaunteth most
In skilful knitting of soft silken Twine;
Nor any Weaver, which his Work doth boast,
In Diaper, in Damask, or in Lyne;
Nor any skill'd in Workmanship emboss'd;
Nor any skill'd in Loups of Fingring fine;
Might in their diverse Cunning ever dare
With this so curious Net-work to compare.
       Edmund Spenser



Course outline

Zoom meeting recordings

Homework schedule

Grade information

Home network map


SMC dates/deadlines


Reading list, per chapter:
 6th edition
 5th edition

Remote Unix accounts


Textbook's website

RFC lookup

Remote Unix access with ssh

Protocols: non-cyber examples

MAC address assignments
 - listing
 - search

TCP/IP - Intro to the IP Protocols

TCP/IP Pocket
Reference Guide
 - IPv4 version
 - IPv6 version

Wireshark doc
html   pdf

Network calculators:
  here's one
  and another
  and a third

Real world DSL
  - a DSL order

commercial routers

Selected protocols






diagnostic protocols

 echo (port 7)

 discard (port 9)

 chargen (port 19) 

 wireshark demo (5m)



FALL 2021
Section 1793 Online

This Website (  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 topics

Grades - 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)

Test - will be given on Canvas under "Quizzes" as "Test2" next Thursday, December 16, from 6:45pm. It is timed, giving you 120 minutes within which to answer the questions. The test will terminate at 8:45 regardless when you start. (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 -
 /etc/hosts  gives "mappings" that pair IP addresses with names
 /etc/resolv.conf  gives hard-coded IP addresses of one or two name servers to use
 /etc/services holds name-to-number mappings for udp and tcp ports (12/9)

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.

Again, technically I should avoid the word "tcp [or udp] process." Maybe "operation" would be better, because "process" has a technical meaning for the operating system and tcp (like the OS itself for that matter) is code that is not embodied in any formal OS process. I'll call it "udp entity" here. I digress.

The question was, what about regulation of the passage of data from the udp entity up to the receiving application process on the data receiver B? While there is a lot of discussion about regulation of horizontal data movement between the transport entities (a major story in tcp's case, and a non-story in udp's), what about the vertical inter-layer handoff? The answer is that the application, and not udp, controls that. Recall the structure of a socket program and that such a program obtains data by calling functions for the purpose named read( ), recv( ), or recvfrom( ). When data arrives at udp for an application, udp puts it into a buffer queue. Each application using udp has its own port number, there is a queue per port number, and the right queue is chosen for an incoming datagram's payload in accordance with the number seen in the datagram's destination port field. Data passage from the front of this FIFO queue to the applicaion is by an application pull, not a udp push. When the application asks for data it gets it in the order in which it was received. If the application doesn't make the call to drain the udp buffer as fast as the network delivers data that fills it, overflow occurs and the data is lost. (12/5)

Homework - per this posting below, we didn't have time to show this during class so please listen to it.
Demo - recording (36m) offering wireshark observations of an ftp file transfer of between computers. The file in question contains the Moby Dick datastream. This will be played over Zoom as part of tonight's class. It is also placed here in case you wish to listen to it separately. (12/2)

No class Thursday Nobember 25. SMC observes Thanksgiving holiday. (11/23)

Remaining calendar - beyond today there are 2 upcoming  Thursday class meetings:
 December 2 - tcp and udp, main topic
 December 9 - http and apache web server, main topic
The SMC College District Calendar shows a final exam period December 14-21. I anticipate giving an online non-cumulative Test2 on current topics. It will be similar to our recent Test1 on the earlier topics. It will probably be scheduled for our class time Thursday, December 16. The posts below give all the homework for the rest of the semester. (11/24)

- for this week
in relation to December 2 lecture:
listen - to the podcast segment at course outline section 11's link entitled "tcp getting connected" which is a general description of the operation of tcp.
read - course outline reading column section 11 about udp and tcp

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)

Homework -for next week
in relation to December 9 lecture:
read - course outline reading column section 13 about "traditional internet applications
  in particular web, mail, and name (dns) service.

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
listen - these discussions about 5 widespread networking utilities, from course outline section 12 Slides column
 ping - "narrated version 24m" link
 traceroute - "narrated version 32m" link (optionally, also "how it works" link in Homework column)
 nmap - "narrated version 43m" link
 netstat - "narrated version 47m" link (optionally, also "discussion of netstat" link in Homework column)
 netcat - "narrated version 39m" link (11/24)

Some test review
(20m) covering a series of related questions from your recent test (21m). (11/19)

Addresses, functions - you know them. Don't get them mixed up.



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)

Please concentrate on dns in preparation for the talk by ICANN guest speaker David Huberman in our November 18 class meeting. His topic will be about DNS abuse, no doubt dealing with the protocol's vulnerabilities and perhaps specific past exploits. To understand what can go wrong with a protocol one must in the first place understand how it works (or is supposed to). So the work suggested below seeks to bring you to the starting line for the talk, and position you to understand and therefore benefit from it.

listen - to these recordings from course outline section 13 in the following suggested order
 recording at link "dns training video"  course outline section 13
 slides at link "DNS protocol" (narrated version)
 slides at link "BIND name server" (narrated version)
 recording at link "managing dns mappings"
 recording at link "Windows dns server"
read - dns coverage in the textbook's chapter 4, pp 69-77
do - the exercise at course outline section 13's link entitled "dns name server -VirtualBox version"  due on sputnik by end of day Sunday November 14.

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)

listen - tbd
do - tbd
read forward -
upcoming topics
 course outline reading column section 11 about udp and tcp
 course outline reading column section 10 about socket API programming 

Deferred in favor of DNS - please see 11/6 Homework posting above


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:
 at UCLA - a Sigma 7 made by Scientific Data Systems of Santa Monica, CA
 at Stanford - a 940 by Scientific Data Systems of Santa Monica, CA
 at UC Santa Barbara - an IBM 360 by International Business Machines of Armonk, NY
 at University of Utah - a PDP 10 by Digital Equipment Corp. of Maynard, MA
It remains heterogeneous today. It's why your Android on Samsung and my Windows on Hewlett-Packard can both access the same credit card or airline reservation databases on somebody's mainframe. (11/4)

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.

Service Server Linux executable Protocol used
name BIND /usr/sbin/named dns
web APACHE /usr/sbin/httpd http
MS sharing SAMBA /usr/sbin/smbd smb
address DHCP /usr/sbin/dhcpd dhcp
socket demo CHOMPER /opt/socketdemo/byteme none
letter upgrade letter upgrade server4 none, really
letter upgrade letter upgrade v2 server4-with-protocol batp*

    *batp - bidirectional alphabet traversal protocol ?


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)

do - the "xinetd" exercise. Mimic my performance of that exercise, whose written instructions are in course outline section 12. I expect to do the exercise step-by-step during our class meeting October 28. You may be able to complete it during the class, following along with me. If not, with aid of the Zoom class recording and the written instructions you can do it on your own. Submit a screenshot from CLIENT in which you access the "byteme" non-network program (networked with the aid of xinetd) at to show its "GIGA-BYTE ME!" output on CLIENT's screen. Please name your screenshot file "xinetd.jpg" (or png). The exercise is done with the same two  machines you used to do the earlier "sniffing" homework. Re-use the scripts from that assignment to produce the two machines needed for this one.  due on sputnik by end of day Wednesday November 3.
read - course outline reading column section 10 about socket API programming  (10/28)

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.
     The exercise in question is the one found in the course outline section 12 at the link entitled "xinetd". It is supported by the last half of the slides in section 10 at the link entitled "Networks" services". (I presented the first half of those last week.) I will present the relevant slides before we do the exercise.
     I plan to do the exercise slowly enough for you to be able to keep up with me. I expect you will want to interrupt me for help if things don't work. Your performance of this lab will not be evaluated in any way. If you can't or don't do it you can just watch me. However I think people get more out of it when they have hands on themselves. So please if you can, have your VB environment available during class and we will have a lab party. (10/27)

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 -
do - the "exercise on internetworking on VirtualBox" in the "Homework" column of course outline section 8. A hands-on counterpart of this exercise, very similar, has been done in the classroom in the past. It involves making addressing and routing choices. I recorded the students' choices on the whiteboard.
Here is a photo of the whiteboard map of a class internetwork built by a previous class. We/you will do similarly. due on sputnik by Sunday October 31  
don't forget - "error detection" per 10/14 Homework posting below (10/21)

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
 Steve Gibson says it's no big deal. (6 min.)
 John Curran says it's a huge, inevitable, immediate problem. (19 min.)
Address depletion rates were diminished by the advent of 1) CIDR as opposed to classfull address block assignments, 2) widespread use of NAT, 3) use of dynamic (recoverable) addresses. Steve says these solutions exceed the problem. John says the problem exceeds these solutions. (10/15)

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 - 
do - the activities in the "Homework" column of course outline section 9
 turning in "error detection," exercise there, due on sputnik by end of day Saturday 10/24,
don't forget - "MAC vs IP addresses" per 10/7 Homework posting below
listen - to the narrated slide presentation about the very important topic of internetworking. Find the link to it in course outline section 7. The link is entitled "(narrated version)". I will not make this presentation in our (Zoom) class. Instead I'll leave it to you to listen to it on your own. In class I will summarize these slides but you will need to see them fully, on your own, my abbreviated summary will not be enough. It is the foundation for the major lab exercise homework coming up in about a week. (10/14)

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? 
 (see also, RIRs) (10/14)

Homework - 
read - everything in the Reading column of course outline section 7
listen - to the recorded demo of forwarding behavior differences of hubs vs switches, Homework column of course outline section 6 (do this at your convenience over the next 2 weeks). During the demo I drew
a sketch. It's of poor quality but available if you want to review it.
listen - to the podcast segment at the link entitled "packet delivery" in the Homework column of course outline section 6
do - "IP packet delivery," course outline section 7 Homework column. It was originally an on-paper assignment. Please do it on paper per the instructions, then scan the resulting 4 pages into 4 image files. Name them: 


(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
do - "MAC vs IP addresses," course outline section 7 Homework column. due on server by end-of-day Tuesday October  19
(Both these assignments focus on the same understanding.) (10/7)

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 - 
read - material in course outline sections 5 and 7
listen - 
physical layer, narrated slides, links entitled "Transmission media" in course outline section 4, and "Signals" in section 5.
- "subnet partitioning," course outline section 7 Homework column. You can do it on paper and send a scan or photo of the paper as a jpg or png file. Or you can put the same information into a text file using txt file extension. Turn in to spunik by end-of-day Wednesday 10/6  (9/30)

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
I performed the exercise while running Wireshark and saved the traffic into capture files. You can open my files in Wireshark, to replay and analyze what I did.

The IP addresses of the machines I used were and 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:
 for section 4:  echo-udp.cap  echo-tcp.cap
 for section 7:  login-telnet.cap  login-ssh.cap
 for section 8:  http.cap 

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's useful to think of a network (a.k.a. subnet) as being defined by a position, and an extent measured from that position, on the continuum of IP addresses represented as a number line. A network is definitively identified by a 2-component ID. The first is its network address and the second is its netmask. 

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 and whose netmask is (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.

A short accompanying, explanatory recorded explanation of performing subnetting.


Homework - 
see/do - the homework column of course outline, section 5 ("netmask legality"). due on sputnik in the "assignments" subdirectory of your home directory end-of-day Wednesday 9/29 
read, specifically -
the write-up at the link entitled "Masks, routing, and subnets" in course outline section 7
view - videos in course outline section 4 homework column
read, generally - readings shown in the course outline and link entitled "Reading list, per chapter." The latter is what I want you to read, from the textbook, for the whole course. Read forward to succeeding sections to prepare for upcoming topics. I will not further specify which items to read when. Read them all, for the entire course, in concert with in-class coverage as we proceed. By now you should have done the readings for sections 1-4 in the course outline. From that point, keep going independently week by week.
anticipate - our next subject, for next week, the arp protocol (address resolution protocol). arp interrelates the addresses of the internet and ethernet protocols in networks that use both (all our common networks do). See course outline topic 5 readings. If you read before next week, next week's lecture will be clearer to you.

Routing - important formulations of the "route" command
Three kinds of routes can appear in a routing table: host route for a specified individual machine, network route for a specified grouping of them, default route as catch-all for everything (unspecified) else. Here are the four key linux command formulations by which you add such routes to a routing table. Though there are 3 kinds of routes, note that 4 command formulations appear. We mentioned the concept of gateways (machines other than the destination, to which you would send the destination's packets for forwarding).  That accounts for there being 2 network route formulations below. One is for the case where the routed-to network is the one you yourself are plugged into, the other for the case where that network is "foreign" or "elsewhere" to you.

Add route to a machine (host route):
  route add -host eth0 
Add route to a group of machines (network route - local) 
  route add -net netmask eth0 
Add route to a group of machines (network route - gatewayed) 
  route add -net netmask gw 
Add route to "any and all" (default route) 
  route add default gw

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:

Netmask: # of one bits: # of zero bits: Implied network size:  24 8 256 (254) 25 7 128 (126) 26 6 64 (62) 27 5 32 (30) 28 4 16 (14) 29 3 8 (6) 30 2 4 (2)


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
--how many protocols does it support? - Apparently the number of protocols supported has reached about 3000.
--who pays these open-source people, anyway? - in most cases nobody. Open source is a labor of love and mostly programmers don't get paid. As for who they are in the case of Wireshark, a list of "contributors" appears at the bottom of the Wireshark man page (that means "manual" page, the traditional form of unix/linux documentation-- give the command "man wireshark" on a linux computer to see it). To my surprise it lists about 1300 people. (9/23)

Homework - 
view and listen - to the several video and audio links in course outline section 4 homework column.
view, listen, read - about undersea cabling at the several links in the post below.
- get started, readings shown in the course outline through section 4; also read forward to succeeding sections as you have time, to prepare for upcoming topics.
do - the "ethernet frames" assignment in course outline section 4 homework column.
due on sputnik in the "assignments" subdirectory of your home directory end-of-day Wednesday 9/22 (9/16)

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:
submarine cable map (click individual cables)
manufacture, shipboard loading, seabed laying youtube video
Haut debit en eau profonde (French)
Transatlantic data cable by Microsoft/Facebook/Telexius completed.
"Contrary to conventional wisdom, satellites play a minimal role in the operation of the internet. Nearly 99% of international phone and data traffic goes through [submarine cables] like ours." Patricia Boulanger, Alcatel Submarine Networks 

Undersea fiberoptic cable landing point (Spain)


What other data link protocols besides ethernet are out there? You might instead have
  point-to-point protocol ("dial up")
  frame relay
  asynchronous transfer mode (ATM)
  802.11 ("wi-fi") in part  

What's the difference?
ARPANet, Leonard Kleinrock's network (now, the Internet), used dedicated connections between computer nodes. He made a phone call to Stanford from UCLA. The wire employed belonged to the phone company. The wire was not used by any other nodes, during the phone call. It was not shared. It was dedicated. Nodes that used it owned it and did not have to compete for it with any other nodes.
ALOHAnet, Norm Abrahamson's satellite based network among islands in Hawaii, used a satellite that could service only one connection at a time, and that all participating computer nodes had to use. So necessarily, nodes had to share it. It was non-dedicated. Nodes that used it did not own it and had to compete for it with all other nodes.
Ethernet was derived from ALOHAnet, and relied on a shared medium too. But while the ALOHAnet medium was radio to the satellite, the ethernet medium was a copper wire. (9/16)

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 


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)

upload - for homework this past week you made a screenshot of Wireshark after it had captured some network traffic. Please upload that file to the "assignments" directory under your home directory on the remote server, using your remote Unix system account. (This is how you will routinely submit homework.) due on sputnik in the "assignments" subdirectory of your home directory end-of-day Sunday, September 12
do - the exercise at the link on the course outline's section 3 entitled "wireshark" It is labeled as "in-class exercise" but becomes homework you will do outside of class.
When you perform it the result will be 3 screenshot files that you produce in the course of performing the exercise:

statistics-udp.jpg (or .png)

I ask you to place these into a zip file named "" 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.

Screenshot, Microsoft's Network Monitor sniffer

(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 (9/3)

Homework - 
1) read all the announcements below and follow all the links they contain. I will expect you to be familiar with the information they convey.
2) do the reading and homework shown in the "Reading" and "Homework" columns of the course outline's topic #1.
3) make progress in installing VirtualBox on your computer, and my delivered VM in VirtualBox (see link below entitled "Obtaining and installing". (9/2)

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.
- Obtaining and installing your VM
     (direct link to fedora31-spring21.ova file on Google Drive)
- Transferring files in and out of it if necessary (accompanying howto video)
- Your VM's configuration
- VirtualBox networking "complete guide" - a good website on the subject

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
Class Census Day: SEP 13, 2021
Class 60% Day: NOV 4, 2021
Last Day to Withdraw to Receive a Refund: SEP 12, 2021
Last Day to Withdraw to Avoid a "W": SEP 12, 2021
Last Day to Withdraw to Guarantee a "W": NOV 20, 2021
Last Day to Request for Pass/No Pass Grade: NOV 20, 2021

Cover art on Tannenbaum textbook:

Networking textbook cover graphic

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.

Phone swithboard operators c. 1950s


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.

The 7 layers of the OSI model

First-day administrative information you will need to know:

Running linux at home.

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.




First message by telegraph 1844

"What hath God wrought?"
May 24, 1844

First message by telephone 1876

"Mr. Watson come here, I want to see you."
March 10, 1876

First message by internet 1969

October 29, 1969