CS70 Network Fundamentals & Architecture

David Morgan
Santa Monica College
see syllabus for email address

Be greater than average
C.A.V.U.

 

Administrativa

Syllabus

Grade information

Course outline

SMC dates/deadlines

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

Remote Unix accounts


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


TechInfo

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
 -
Analysis

commercial routers


Selected protocols

ARP

IP

ICMP

TCP

UDP

echo (port 7)

discard (port 9)

chargen (port 19)

 


 

FALL 2019
Section 1795  9:00a - 12:05p Sat Bus 263

This Website (http://homepage.smc.edu/morgan_david/)  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

Homework
do
- this exercise on internetworking, which extends the one we did in class. This is to be done on DETER, remotely, using the DETER accounts issued to you.
what to turn in - as the product of this assignment, please make a screenshot of the web page you get at the end of the exercise in the subsection "5. Port forwarding" of the section "Tasks." (This will be the screen on NWworkstation1 that is obtained there when you execute the lynx browser to get content from the web server located on SWworkstation1.) Send the screenshot to me as an email attachment to morgan_david@smc.edu please. - will be due at the end of the course.
(10/19)

Respond within 72 hours please - to an auto-generated email message from DETER that you will receive at your SMC email address. I will create DETER accounts for you. The email message should be self-explanatory and requires a password change within 72 hours. (10/19)

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 Sunday 10/20.
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")  (10/14)

Today's plan - slides at link "IP addresses." Followed by slides "internetworks" to prepare for next week's all-day group lab exercise. Followed by slides "Error detection" to enable the related homework due next week. (10/12)
post-facto check: we did not cover "IP addresses" however traceroute came up and we talked about that. (10/14)

In-class exercise to build an internetwork - will occupy the entire 3 hours, no lecture. Planned to be performed October 19. Please review the instructions in advance. Here is the photo of the whiteboard map of the class internetwork built by a previous class. We/you will do similarly. (10/12)

Grades - have been posted, link entitled "Grade information" at left. Grades include the subnet partitioning exercise. (10/12)

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. (10/12)

Midterm exam reading - there will be a midterm. Please see the "Readling list, per chapter" link, above left, which indicates which chapters' material will be covered by the exam. Continue reading with the aim of reading all those chapters by the midterm date, upcoming. (10/12)

Grades - have been posted, link entitled "Grade information" at left. Grades include the frames and netmask legality exercises. (10/2)

In-class exercise today - we will perform the "ifconfig/route" exercise from course outline section 5. (9/28)

Grades - have been posted, link entitled "Grade information" at left. Look yourself up by your constructed anonymous ID number (also used as you sputnik.smc.edu password). Because sputnik was down, you may turn in the "ethernet frames" now. You should have done the assignment, and held the required file awaiting sputnik. So please upload frames.txt by tomorrow night, Sunday 09/29 (9/27)

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

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

A related description of the thinking process comes from our textbook, Computer Networks and Internets, Douglas Comer (see p. 368 fifth edition). (9/27)

Homework - 
do - "subnet partitioning," course outline section 7 Homework column. Turn in on paper in class Saturday October 5
do - "IP packet delivery," course outline section 7 Homework column. due on paper in class Saturday October 12
do - "MAC vs IP addresses," course outline section 7 Homework column. due on sputnik end-of-day Saturday October 12
(The latter two assignments focus on the same understanding.) (9/27)

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? (9/27)

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 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:

(9/21)

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 Sunday September 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.
(9/21)

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 192.168.4.2 eth0 
Add route to a group of machines (network route - local) 
  route add –net 192.168.4.0 netmask 255.255.255.0 eth0 
Add route to a group of machines (network route - gatewayed) 
  route add –net 192.168.5.0 netmask 255.255.255.0 gw 192.168.4.1 
Add route to “any and all” (default route) 
  route add default gw 192.168.4.1

Study these commands intently and try to internalize the semantic meaning they embody. (9/21)

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. (9/21)

Network size for common netmasks:

Netmask: # of one bits: # of zero bits: Implied network size:
255.255.255.0  24 8 256 (254)
255.255.255.128 25 7 128 (126)
255.255.255.192 26 6 64 (62)
255.255.255.224 27 5 32 (30)
255.255.255.240 28 4 16 (14)
255.255.255.248 29 3 8 (6)
255.255.255.252 30 2 4 (2)

(9/21)

Lego project - make a router for your toy trains. (How is this an applicable analogy to the processing of frames within a computer router?) (9/21)

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 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:
 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.  (9/14)

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. (9/13)

Homework - 
see/do - the homework column of course outline, section 4 ("ethernet frames"). due on sputnik in the "assignments" subdirectory of your home directory end-of-day Sunday 9/22 (9/13)

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 (9/13)

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. (9/13)

Homework - 
read - 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.
listen - to Bob Metcalfe talk about inventing ethernet.
(9/7)

Grades - have been posted, link entitled "Grade information" at left. Look yourself up by your constructed anonymous ID number (also used as you sputnik.smc.edu password). (9/7)

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. (9/7)

Screenshot of Microsoft Network Monitor courtesy of a former student. Compare the interface with Wireshark's.

Screenshot, Microsoft's Network Monitor sniffer

 

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.  (8/31)

First-day handout - explaining use of class computers.

A Remote Unix system account will be created for you.

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:

What SMC's wireless internet access service doesn't do - everything! (with one big exception). SMC's web page entitled "Wireless Internet Access at SMC" tells you what their service does not do:

"What network services are available?

"Only web access is allowed (http and https). Campus network ports and the wireless network do not allow access to any non-web services such as telnet, FTP, SMTP, POP, IMAP, etc."

At this early stage in the course do you know what that means? I'm not sure. If you don't, you will soon. But if you try to have the service do anything that it doesn't (clean your socks, chill your beer, connect to a remote machine with ssh...) I hope you won't ask me why it didn't work.

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.

Opportunity - I'm happy to tell you that as a class we have the fortunate invitation to use a network testbed facility operated by USC/ISI called DETER. I will request individual DETER accounts for you; when they are created you will get an email message with info and credentials. In class I will describe DETER and how we will use it. This will come some weeks into the semester. In the meantime, you can explore the links under the heading "DETER net testbed" at left if you like.


 

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

"lo"
October 29, 1969