CS70 Network Fundamentals & Architecture

David Morgan
Santa Monica College
see syllabus for email address

Be greater than average




Grade information

Course outline

SMC dates/deadlines

Zoom meeting recordings

Home network map

Homework schedule

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

Remote Unix accounts

DETER net testbed
  get/use an account
  news report (pbs)


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






echo (port 7)

discard (port 9)

chargen (port 19)



FALL 2020
Section 4116  6:45p - 9:50p Thu remotely via Zoom

This Website (http://classpage.dmorgan.us/)  will be used extensively to communicate with you. Announcements, grade reports, and assignments will be posted here. Please access the website from any SMC computer lab. Alternatively, it can be viewed from an internet-connected browser anywhere. You are responsible for awareness of the information posted here.

Announcements/grades/current topics

Grades - have been updated, link entitled "Grade information" at left.  They include the  "IP packet delivery" assignment, featuring Sally and Harry. Please call any anomalies to my attention. (10/15)

Homework - 
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 Wednesday 10/21,
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 foundatin for the major lab exercise homework coming up in about a week.
listen - if you did not do it as assigned in the 10/8 homework posting below, listen to the "packet delivery" podcast snippet in the "Homework" column of course outline section 6 (relating to Sally & Harry and the 2 golden rules)
listen - to the "how it works" podcast snippet in the "Homework" column of course outline section 12 (relating to traceroute; Windows has command "tracert" while linux and apple have "traceroute") (10/15)

Upcoming homework - preview it if you wish, will be assigned next week
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...TBD  (10/15)

A real-world DSL order - We have been emphasizing what a "network" is in technical, mathematical terms. It's a range of numbers that people express by telling other people what the first number in the range is (network address), and how many numbers there are in it (netmask). This surfaces in the commnuique I received once when I ordered a subnet from an ISP. Please see the links in the column at left under the heading "Real world DSL." Read the analysis. (10/15)

Who was IANA? What about now? Where are they? What is their job? (10/15)

Grades - have been updated, link entitled "Grade information" at left. The current "subnet partitioning" assignment is not due till the end of the day. For those who have already turned it in, I graded it and posted those assignment grades. However they have not yet been incorporated into the overall cumulative average grades. Also new are the individual grades I have entered or changed in response to email communication with some of you in the past week. Please check your grades and let me know of any anomalies. (10/8)

Golden rules for deciding how to ship a packet (Fore Systems "IP packet delivery"):

We reviewed the concept behind the "IP packet delivery": if IP thinks a destination IP address is local it arps for that IP address, if not it arps for the IP address of its default router (which comes from the routing table). Everything hinges on what "local" means. That is a function of the given destination address, the local address, and the local netmask. Network calculators and/or the linux "ipcalc" command can help you recreate IP's "thinking process" in this regard for particular subnets, addresses, and netmasks.

A related description of the thinking process comes from our textbook, Computer Networks and Internets, Douglas Comer (see p. 368 fifth edition). (10/8)

Homework - 
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 14
do - "MAC vs IP addresses," course outline section 7 Homework column. due on server by end-of-day Sunday Octoberl 18
(Both these assignments focus on the same understanding.) (10/8)

Opportunity - NASA Community College Aerospace Scholars (10/8)

Home network map - because sometimes in class I refer to my home network for illustration of certain points, I've made a diagram of it. (10/3)

Homework - 
read - material in course outline sections 5 and 7
- "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 Thursday 10/7  (10/1)

Double match?? - what would happen if an IP packet's destination address matched two entries in the routing table. To which of the two interfaces would it be sent? Is this even possible? (10/1)

Packet capture files for you from the "wireshark" in-class exercise
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.  (10/1)

Grades - have been posted, link entitled "Grade information" at left. Grades include the upload of "introduction.txt" (or any other file) and upload of the wireshark capture screen printout. Please check your grades and let me know of any anomalies. (9/23)

Network Address  +  Netmask  =  Subnet
It'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 9/30   (and see also the 9/17 Homework posting below, other assignment also due 9/30)
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. (9/24)

Windows route command - differs in syntax and scope somewhat from the linux command of the same name. But it is kindred in spirit and operates on the very same internet protocol (though not the same coded implementation of it). The internet protocol is defined outside Microsoft and outside linux. Both Microsoft and linux programmers  have taken their hand to writing programs that do what the protocol defines. Including a "route" command to manipulate the protocol's route table. In Windows, open a command box and execute "route print" if you wish to see the route table. (9/24)

Network size for common netmasks:

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?) (9/24)

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. (9/24)

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 9/30 (9/17)

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 (9/17)

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 (9/17)

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. (9/17)

Homework update - green light for homework in 9/10 posting below
The instructions for the Wireshark homework have been updated for our VirtualBox environment. As well, and importantly, new material about "provided scripts" has been added to the original "Obtaining and installing" instructions. Please read the additional instructions, get the scripts they refer to from Google Drive, and proceed with the instructions in the course outline's section 3 for doing the wireshark exercise. 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 "wireshark-homework.zip" and upload it to your assignments directory. (Please ignore the questions you will see at the bottom of the assignment page. They are not for you. I only want the screenshots.)

Please start this assignment before Thursday's class. At class I will spend a little time making sure the assignment and steps to perform it are understood. We will also decide a due date then. due on sputnik in the "assignments" subdirectory of your home directory end-of-day Friday, September 25 (9/15)

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.)
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. Please wait to do this until I have a chance to edit the instructions, so that they will accord with our remote environment and the virtual machines. After I have done that I plan to send you a "green light" email message. (9/10)

VM files on Google Drive - I have asked students to download some files from OneDrive. Some of you have not yet done so or encountered problems in doing so that we have not solved.  I have placed a second copy of the files elsewhere, namely on Google Drive. I have also emailed you an access link today. Please copy it into a browser. It should take you directly to a screen offering you the files. If you have not yet obtained the files from OneDrive as originally instructed, please try to get them from Google Drive now instead. (9/10)

RFC process - how protocols get created. Here is a current example, HTTP 2 which was published as an RFC in May, 2015. See in particular the development timeline that has led it to this point. (9/10)

Screenshot of Microsoft Network Monitor. Compare the interface with Wireshark's. It demonstrates the product category (network "sniffers") to which both products belong.

Screenshot, Microsoft's Network Monitor sniffer


Link to tonight's class (This is hosted at my home. I don't know if upload speed will be a problem for you to listen to the recording. Let me know if so please.) (9/3)
[ see link at left entitled "Zoom meeting recordings" ]

Course outline - with approximate weekly topic coverage corresponded to related readings, homework assignments, and in-class slides I will use. Please follow this outline as we move through the topics, for assignments and reading I want to assign.

Homework - 
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.  (9/3)

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
- Transferring files in and out of it if necessary
- Your VM's configuration
- VirtualBox networking "complete guide" - a good website on the subject

A Remote Unix system account is available for your use.

Internships - a link I have been asked to publicize to students. (8/30)

Using ssh (secure shell). ssh is an important tool you will use for interacting with remote computers. For that you will need an ssh client. There are a number of ssh client alternatives.

Distributing files from sputnik to the class as a whole,  publicly - the above file transfer discussion describes file movement to and from your own home directory, exclusive to you. Sometimes I will want to have someplace to put a file so everybody can get to it and download it. When I do that, here's how to download them.

Cover art on Tannenbaum textbook:

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