CS522 Questions and Answers

Reset password 9/30/2003

Dave Lohman, our system admin, has reset the passwords of CS522 class so that zeppo our sun enterprise server can be accessed for hw3 exercises. Let me know if you have problem access your account. 4 of you has multiple middle names or no middle name need to use just first and last initials with 4 last digits of your student ID.

-----Original Message-----
From: David Lohmann [mailto:lohmann@hawkeye.uccs.edu]
Sent: Tuesday, September 30, 2003 4:31 PM
To: chow@cs.uccs.edu
Subject: Passwords for Zeppo

I've changed passwords for all students in CS 522 to allow login
on zeppo. Solaris does not allow the first 8 digits of the
student ID so I used first initial, second initial, last initial,
last four digits of the student ID.

I will place a class list in you mailbox indicating the passwords
of accounts that do not fit the pattern.

Please let all students know their new password. They will not
be able to login to any of the Linux/Solaris systems until you
give it to them.

If they would like to change their password, they may use yppasswd
on zeppo and that will change it on all systems. If they try that
on the Linux systems they will not be able to login to zeppo.

Thank you,
David Lohmann

the 169.254.0.0 is the windows Automatic Private IP Addressing(APIPA).

On blanca, we have the following routing table entry.

blanca.uccs.edu> netstat -rn
Kernel IP routing table
Destination   Gateway       Genmask       Flags MSS Window irtt Iface
128.198.160.0 0.0.0.0       255.255.224.0 U     0   0      0    eth0
169.254.0.0   0.0.0.0       255.255.0.0   U     0   0      0    eth0
127.0.0.0     0.0.0.0       255.0.0.0     U     0   0      0    lo
0.0.0.0       128.198.160.1 0.0.0.0       UG    0   0      0    eth0

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Monday, September 15, 2003 1:16 PM
To: 'Sai Nandoor'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: cs 522 hw 2

Sai,

Here is the hint.
The destination MAC address in the Ethernet frame is used by the network
interface card of the receiver to decide whether it matches with the
burned in MAC address of its Ethernet card or interface card. If it
matches, the frame data is receive and its information field delivered
to the upper network layer for processing.

Edward

-----Original Message-----
From: Sai Nandoor [mailto:sainandoor@hotmail.com]
Sent: Monday, September 15, 2003 12:14 PM
To: chow@cs.uccs.edu
Subject: cs 522 hw 2

Dear Dr.Chow,
In problem 3 part e, when blanca tries to send a message to DNS server
128.198.1.250 will it use the MAC address of this machine (which is
00-02-b3-90-d9-3e) as the destination MAC address or will it use the
default
gateway MAC address (which is 00-00-0c-07-ac-01) as the destination MAC
address since the two machines are not on the same subnet?

From,
Sai Nandoor

hw1ex2.1: Receive 404 file not found and the response did not show Server header

Reason: It may be due to the missing space character between the url and HTTP protocol version number.

s.j.adair@att.net says:
Dr. Chow,
cedwardchow says:
hi.
s.j.adair@att.net says:
I am working on hw ex2. Before the questions you tell us to try telnet www.uccs.edu 80 and find out the web server that is running.
s.j.adair@att.net says:
I just did that and just get the Trying 128..
s.j.adair@att.net says:
Connected to
s.j.adair@att.net says:
Escape char
s.j.adair@att.net says:
so, I typed GET /HTTP/1.0 and see
s.j.adair@att.net says:
Apache/1.3.27 Server at www.uccs.edu Port 80
s.j.adair@att.net says:
I assume that is the web server?
s.j.adair@att.net says:
Thanks-
cedwardchow says:
yes. it is. The server header indicates that.
cedwardchow says:
It also indicates other related software package used with the apache web server.
s.j.adair@att.net says:
I did not see a SERVER: line in this interaction. It was buried in the html as <ADDRESS>Apache...
cedwardchow says:
It should show up at the very begining of server http response.
cedwardchow says:
right after HTTP/1.1 200 OK
Date: Tue, 02 Sep 2003 18:16:23 GMT

s.j.adair@att.net says:
It isn't, I am emailing you the entire out2.txt file. I did it by using putty to ssh to sanluis and then did the telnet to www.uccs.edu
cedwardchow says:
Let me read your out2.txt file.
cedwardchow says:
HTTP/1.1 200 OK
Date: Tue, 02 Sep 2003 18:16:23 GMT

cedwardchow says:
requested URL /HTTP/1.0 was not found on this server
cedwardchow says:
From the response, it indicates it is 404 file not found response.
cedwardchow says:
You may have type in the incorrect http request.
cedwardchow says:
you should have GET followed by a space character, then followed by "/" , then followed by another space, finall the "HTTP/1.0"
cedwardchow says:
You did not have a space character between / and HTTP/1.0
cedwardchow says:
Therefore the server try to interpret the "/HTTP/1.0" as the url or file you try to request.
s.j.adair@att.net says:
Thank you! It works much better now!
cedwardchow says:
Great.

Using netsh to set IP address of an interface

$ netsh interface ip set address name="Local Area Connection" source=static add
r=192.168.0.100 mask=255.255.255.0
Ok.

$ipconfig

...
Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 192.168.0.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.0.1

Set primary DNS server address:

netsh interface ip set dns name=<the name of your network card>
source=static addr=<your DNS IP address> register=primary

---

for example:

netsh interface ip set dns name="Ethernet Broadcom 440x 10 100 built
in" source=static addr=243.234.0.15 register=primary

Set secondar DNS server address :

netsh interface ip add dns name="Ethernet Broadcom 440x 10 100 built
in" addr=243.234.0.16 index=2

Question project:Choosing Semester Projects related to web services

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Sunday, September 29, 2002 5:42 PM
To: 'Ramarao Desaraju'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: CS 522 Semester Project

Ramarao,

I would prefer to have projects tie the java web service package study
with certain network services/protocols. The title can be "Apply Java
Web Services Developer Pack to yyy".
http://java.sun.com/webservices/webservicespack.html
Example of network services:
Instant Messaging (Jabber) http://www.jabber.org
Dynamic cache services,
JESI,
active web query,
timestamp service,
authentication services (e.g., work on PEAP, 802.1x). Any emerging
protocols (see IETF documents).

You can also look at the specific aspects of java web services and try
to see if they can be improved. These include security, reliability,
performance, benchmarking.

I will be happy to guide you in selecting specific network services or
protocols.

I do not want the projects to be just a generic survey without in-depth
study/applications.

I believe there are quite a few of you interested in web services (some
of you interested in MS .NET; some of you interested in Java Web
Services.) But the above is my general guideline for choosing web
services related projects.

Edward

Question: hw3ex3: Explain byte ordering problem using mathematical equation.

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Sunday, September 29, 2002 11:25 AM
To: CS522@cs.uccs.edu
Cc: Edward Chow
Subject: CS522 ex3.3

Dear class,

For ex3.3, I am expecting the answer to be more precise so I add
"Specify the relationship between the values sent and the value received
mathematically based your understanding of byte ordering."
For example, if you send sessionID as 63 but zeppo receives 1056964608,
send x as 7 and receive 1792.
Note that 1056964608/63=16777216; log2(16777216)=24. 1792/7=256;
log2(256)=8. Explain why 2^24 and 2^8 play a role here between the
values sent and received.

Edward

Use pens to send this pen message on wetterhorn to penr on zeppo.
set pen.x with the last digit of your SS#. Here we use -x 8 option to
set it to 8.
set sessionID with the first two digits of your SS#. Here we use -i 45
to set it to 45.
Document what penr reports on zeppo.
Discuss why the values of session ID and x are interpreted differently.
Specify the relationship between the values sent and the value received
mathematically based your understanding of byte ordering.

Question: Packet lost in the channel will not be detected by the sender or receiver.

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Sunday, September 29, 2002 10:46 AM
To: 'Ramarao Desaraju'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: CS 522 Homework #3 Solutions

Ramarao,

When C2 lose A0, both sender and receiver will not detect such event.
Er is intended for receiving garbled msg.
Therefore (4,3,E,E)--R:Er-->(7,3,E,E) in the following sequence is not
correct.

(4,3,E,A0)--C2:-lose A0-->(4,3,E,E)
(4,3,E,E)--R:Er-->(7,3,E,E)

Edward

Question: hw2ex2.1: Why ARP is sent before DNS request.

KeG0733 : Dr Chow?
cedwardchow : yes. identify yourself
KeG0733 : hi..this is Kevin Gigax from CS522
KeG0733 : trying to complete assignment 2
KeG0733 : I am also confused about the ARP and DNS protocols
cedwardchow : yes.
cedwardchow : You got 25/25 for hw2ex4.
cedwardchow : explain the problem.
cedwardchow : and why you are confused.
KeG0733 : Well, I am not sure what the ARP request is trying to get
KeG0733 : b/c before we send out a DNS request, we do not know the IP address that we are trying to connect to
KeG0733 : I guess I am unsure what the ARP request is returning
KeG0733 : Is it the MAC address of the router that I am going out of my subnet on?
cedwardchow : DNS request need to be sent to the DNS server.
cedwardchow : But DNS server's IP address turns out to be not a IP address belongs to the local subnet.
cedwardchow : It needs to be relayed by the default gateway.
cedwardchow : We know the gateway IP address but the first time we start it up we will need to find its MAC address.
cedwardchow : That is the reason why ARP request is sent and ask for who own the gateway IP address 128.198.167.254.
cedwardchow : The gateway replies with ARP response that contain the MAC address associated with 128.198.167.254.
KeG0733 : ok...so the destination MAC address is the MAC address of our default gateway?
cedwardchow : In this case, it is. But depends on the packet destination.
cedwardchow : if you try to send a packet to wetterhorn from sanluis, they are all in the same subnet. In that case, the MAC address of wettherhorn will be used as destination MAC address.
KeG0733 : ok...that helps my understanding...thx
cedwardchow : You are welcome.

Question related to hw2ex3:Analyze the Signal Propagation Delay/Transmission Delay/Queueing Delay on traceroute resutls.

The following are discussion captured on Microsoft Messenger.

Never give out your password or credit card number in an instant message conversation.

chow@cs.uccs.edu says:
hi
chow@cs.uccs.edu says:
Is this Ed?
Terri says:
yes
chow@cs.uccs.edu says:
You got 25/25 for hw2ex4.
Terri says:
Thanks. I had a couple of questions about exercise 3.
chow@cs.uccs.edu says:
yes.
Terri says:
for the last question regarding the round trip time being shorter, is it because a different path is being taken back to the source machine
chow@cs.uccs.edu says:
most of the path to router 11 overlap with that of the path to router 10 ( has one more link segment between router 10 and router 11 and router 11.
chow@cs.uccs.edu says:
longer path but shorter time.
Terri says:
so there are more links than going than coming back if I understand?
chow@cs.uccs.edu says:
2 more links and one mre router.
chow@cs.uccs.edu says:
round trip
chow@cs.uccs.edu says:
Those msg to router 10 go through 10 link segments and 9 intermediate router each way.
Terri says:
makes sense. for the equation i have it as twice the delays for routers i=1..x-1 plus the queueing delay for the last router. also how do you account for the delay between the source machine and router one. i just assumed a queueing delay at this point. I can send you my word document so you could take a look.
chow@cs.uccs.edu says:
Sure.
Terri says:
great. I'll send it to you in just a second please let me know when you get it.
chow@cs.uccs.edu says:
It is up to you to model whether there is a queueing delay on the hosting machine's network interface. You can assume the host machine is not busy.
Terri says:
I just sent you my word document
chow@cs.uccs.edu says:
got it.
Terri says:
I drew the diagram and explained it in words so it should be easy to follow what I did.
Terri says:
Sorry the message says Terri. she's the only one with a hotmail account.
chow@cs.uccs.edu says:
You can assume that the return path is the same as the forwarding path for the three ICMP packets to router 10 and the same paths are used for those three msg to router 11.
chow@cs.uccs.edu says:
The experiment done by Vern Paxon and others show that the routing path rarely changed.
Terri says:
are you talking about the equation or the last question regarding the change in round trip time?
chow@cs.uccs.edu says:
The equation is fine. But if it applies to obtain the difference of roundtrip delay between router 10 and router 11, then you can simplify it.
chow@cs.uccs.edu says:
The word "slight variant in queueing delay" has no basis.
chow@cs.uccs.edu says:
How do you know it is "slight"?
Terri says:
I was assuming that the amount of traffic back could hypothetically be slightly higher or less on the return trip.
chow@cs.uccs.edu says:
That is a big if. You can have a more general assumption. Kimberley kaffe at UCSD done some roundtrip experiments and find indeed some path has un-even traffic volume.
chow@cs.uccs.edu says:
But you can use that to explain clearly what we oberved here.
chow@cs.uccs.edu says:
I should say cannot.
Terri says:
So I think I'm done with my homework then unless you think I should rephrase my answers to the last exercise.
chow@cs.uccs.edu says:
Should I restrict the answer by adding the path is not changed over all experiments?
chow@cs.uccs.edu says:
I would say your answer to 3.3 is not quite correct.
chow@cs.uccs.edu says:
You attribute the cause to different path but it could be other reasons-queueing delay.
Terri says:
rereading what I have. please give me a minute. thanks
chow@cs.uccs.edu says:
I would like some analysis that compare the terms in the formula.
chow@cs.uccs.edu says:
the two formula.
Terri says:
So I should base my answer to 3.3 on what I came up with in my equation?
chow@cs.uccs.edu says:
definitely. Apply your equation to find out the difference between the round trip tiimes. You then can explain why the result is negative.
chow@cs.uccs.edu says:
(roundtriptimeof router(11)-roundtriptimeofrouter(10))
Terri says:
okay. I'll rework 3.3 and talk to you Monday. What is the difference between the three times listed in the traceroute command though.
chow@cs.uccs.edu says:
10 mdf3-bi4k-2-eth-1-1.rwc1.attens.net (216.148.209.66) 38.866 ms 38.651 ms 38.282 ms
11 www.redhat.com (216.148.218.197) 35.488 ms 35.469 ms 35.380 ms

chow@cs.uccs.edu says:
35.488 -38.l866=-3.378

chow@cs.uccs.edu says:
it is negative.
Terri says:
sorry. what i meant was why does traceroute list 3 different times for each router
chow@cs.uccs.edu says:
The sending machines send out three different ICMP reqeusts.
chow@cs.uccs.edu says:
note path we specify spd not as spd(i,t). It implies the propagation delay is fix and not change. therefore the distance of link segment is fix and not changed.
Terri says:
okay. I'm going to go work on my homework some more. I will talk to you Monday afternoon. Thanks.
chow@cs.uccs.edu says:
The discussion is very help. I would like to post this discussion to our Q&A web page if you do not mind.
Terri says:
no problem.
chow@cs.uccs.edu says:
bye. Have a good weekend.
Terri says:
by

Question: HW2Exercise 2. End Host Routing.

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Friday, September 13, 2002 1:57 PM
To: 'Pham, Thao'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: CS522 homework2 exercise 2

Thao,

I add the following hints for hw2ex2 and updated the homework web page
to include them also. I hope it helps. Let me know.

Edward

Exercise 2. End Host Routing.
Assume we use the lynx text-based browser to retrieve an 802.1x related
powerpoint presentation.
"lynx http://www.drizzle.com/~aboba/IEEE/BAWUG.ppt" on sanluis.uccs.edu.

Questions:
1. For the above web retrieval, what network services are used by
sanluis.uccs.edu? In what order?

Hint. Look at the handout
http://cs.uccs.edu/~cs522/intro/index.html#msgs4WebAccess
on "Messages generated for a simple web access".
Especially, observe the protocol in the protocol field generated by
Ethereal for all frames generated. They give indication of what protocol
or network services are used.

2. For the Ethernet frame that contains the HTTP request sent by lynx
for this request, what are the destination and source IP addresses in
the IP header and the destination and source MAC addresses in the
Ethernet Frame? Explain how you find the information.
There are three routing table entries on sanluis.uccs.edu's routing
table.

Hint. For the frame sent by the sanluis for the HTTP request, first you
identify who is the sender and who is the receiver of the http request.
Based on the domain names of the sender and the receiver, you can then
use "dig <domainname", "host <domainname>", or "nslookup <domainname>"
to find out the corresponding IP address of the domain name. Those
commands use DNS protocol to retrieve the IP address mapping.
For the source Mac address, it is related to the Ethernet address
associated with the sending machine, sanluis.uccs.edu. As indicated in
"PC Network Setup"
http://cs.uccs.edu/~cs522/intro/pcnetsetup/pcnetsetup.htm,
/sbin/ifconfig can be used to find out the IP address assignment to a
specific network interface card. For example, we get the following
result on lamar.uccs.edu

[root@lamar root]# /sbin/ifconfig
eth0 Link encap:Ethernet HWaddr 00:06:5B:62:FE:A5
inet addr:128.198.60.168 Bcast:128.198.60.255 Mask:255.255.255.128
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:4715180 errors:0 dropped:0 overruns:1 frame:0
TX packets:71023 errors:0 dropped:0 overruns:0 carrier:1
collisions:0 txqueuelen:100
RX bytes:345321859 (329.3 Mb) TX bytes:9466097 (9.0 Mb)
Interrupt:11 Base address:0xdc00

It indicates that the Ethernet card has a MAC address of
00:06:5B:62:FE:A5.
You can run the same command on sanluis to find the source MAC address
for the frame.

The frame sent by sanluis will be forwarded to the default gateway of
128.198.160/24 subnet, then the IP packet in the frame payload will be
routed to www.drizzle.com. Therefore, the destination MAC address of the
frame sent by sanluis will be the MAC address associated with the
default gateway. The default gateway IP address can be found in the
routing table. The arp table contains the cached IP address and MAC
address mapping. See "PC Network Setup"
http://cs.uccs.edu/~cs522/intro/pcnetsetup/pcnetsetup.htm which discuss
the related commands for finding those info.

3. For an IP packet destined to 128.198.162.68, explain which routing
table entry will be picked and used in sending the packet out.

-----Original Message-----
From: Pham, Thao [mailto:Thao.Pham@hp.com]
Sent: Friday, September 13, 2002 9:55 AM
To: chow@cs.uccs.edu
Subject: homework2 exercise 2

Dr. Chow,

I was looking at this excercise and I am at a loss as to how to start
carrying out this assignment.
Would you please provide guidance on this?
thanks,

Thao L. Pham

Question relate to CS Unix machines: How can we see our home directory no matter which CS Unix Machines we log in?

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Monday, September 09, 2002 2:15 PM
To: 'Detorie Casey C Capt SWC/SOPSC'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: Networking question

Casey,

The CS Unix machines (cs, wetterhorn, redcloud, shavano, crestone,
sanluis, blanca, zeppo) all have Fast Ethernet Network interface cards
(100Mbps) that connect via cat 5 twisted pair cable to HP 4000 switch,
which has a gigabit fiber port that connect to the UCCS computing
service CISCO router.
They belong to subnet 128.198.160.0/21 and was assigned with
128.198.162.x address, (cs.uccs.edu is 128.198.162.68, blanca is
128.198.162.60).

Network File System (NFS) client is run on all those machines with
cs.uccs.edu being the NFS server which has the physical disks that
contains files of our home directories. At the boot time, the file
system /usr2/students is mounted. See the attached mount command result
on blanca.uccs.edu.

When the NFS client machine tries to access file in directory that under
file type of NFS. The operating system will detect that can issue NFS
request to the NFS file server on cs.uccs.edu to retrieve the
corresponding block of data. For efficient reason, NFS uses UDP protocol
instead of TCP. Since one can login to multiple machines and edit the
same file, the NFS file system needs to consider file lock mechanism to
ensure the integrity of the files. Since all file updates are going to
cs.uccs.edu, it may take some time for the data to actually get there if
the system is busy. Normally it is rather quick.

Hope that answer your question.

Edward

CS 522blanca.uccs.edu> mount
/dev/sda3 on / type ext2 (rw)
none on /proc type proc (rw)
usbdevfs on /proc/bus/usb type usbdevfs (rw)
/dev/sda1 on /boot type ext2 (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
none on /dev/shm type tmpfs (rw)
blanca:(pid987) on /net type nfs
(intr,rw,port=1023,timeo=8,retrans=110,indirect,map=/etc/amd.net,dev=000
00009)
cs:/usr2/faculty on /.automount/cs/root/usr2/faculty type nfs
(nosuid,nodev,dev=0000000a,vers=3,proto=udp)
cs:/usr2/research on /.automount/cs/root/usr2/research type nfs
(nosuid,nodev,dev=0000000b,vers=3,proto=udp)
cs:/usr2/students on /.automount/cs/root/usr2/students type nfs
(nosuid,nodev,dev=0000000c,vers=3,proto=udp)

-----Original Message-----
From: Detorie Casey C Capt SWC/SOPSC
[mailto:Casey.Detorie@schriever.af.mil]
Sent: Monday, September 09, 2002 8:35 AM
To: chow@cs.uccs.edu
Subject: Networking question

Dr. Chow:
Can you explain how the various Unix machines in the uccs.edu domain
(ie.
wetterhorn, sanluis, etc.) are interconnected? How is it that when one
logs
on to wetterhorn and alters a file, that change is reflected when one
views
the file on sanluis? Is it that the network automatically updates these
changes on each user's home directory on each individual machine, or
does
each user have exactly one home directory, and wetterhorn, sanluis, etc.
all
have access to it?

Casey Detorie

Question related to web page setup:

-----Original Message-----
From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Wednesday, August 27, 2003 12:06 PM
To: 'Malillos, Esquivel'
Cc: Edward Chow; CS526@cs.uccs.edu; CS522@cs.uccs.edu
Subject: RE: cs 526

Esquivel,

It is a unix file protection mechanism and a common web site setup
mistake. We will cover that today.

Basically, your home directory is protected with only "owner" access.
Others including that of web server running as an account called apache
CANNOT access files/directories in your home directory or public_html
directory.
You need to perform the following command in your home directory to open
up the access a bit.

chmod 755 ../<your login>

Here substitute <your login> with your CS Unix login.
Also make sure the public_html directory and the files in it have 755
access right permission. You can use the following command

chmod -R 755 public_html

Make sure all new files or directories you create for web access has
same file permission. You can add "umask 022" to your shell profile that
will create files with 755 access right pattern.

Edward

-----Original Message-----
From: Malillos, Esquivel [mailto:esquivel.malillos@hp.com]
Sent: Wednesday, August 27, 2003 11:23 AM
To: chow@cs.uccs.edu
Subject: cs 526

Dr. Chow,

I cannot setup my personal web page. I cannot drop by your office on
your normal office hour so directing me thru email is very appreciated.
I already have an account but I got a "forbidden" msg whenever I access
http://cs.uccs.edu/~ecmalill so I need to change the access rights.
Where should I telnet to?

Thanks.
Esquivel Malillos - CS 526 Student

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Wednesday, August 28, 2002 10:53 AM
To: sirubey@excite.com
Cc: 'Edward Chow'; CS522@cs.uccs.edu
Subject: RE: login

Sid,

I just checked your home directory and found that you have not open up access permission for other to look into your home directory. System admin set up that way to protect you. But I and web server needs read and execute permission to look or retrieve documents for processing. It is a common problem for first time web designer/publisher on unix system.

Please change your home directory permission by executing the following command in your home directory:

chmod 755 ../<login>

Here <login> is sirubey.

For the public_html directory and any web documents you create, you need to do that same thing

chmod 755 public_html
cd
chmod 755 *

You may want to change the umask command in your Unix profile from

Umask 077

To

Umask 022

That will allow future files to be created to allow others with read/execute access.

Note that I am sending this email to our class net aliase CS522@cs.uccs.edu, since many of you may face the same problem. Make sure you create .forward file to forward your email to your prefer mail server at excite.com.

Drop by my office if you still have problem.

Edward

-----Original Message-----
From: Sid [mailto:sirubey@excite.com]
Sent: Tuesday, August 27, 2002 11:49 PM
To: chow@cs.uccs.edu
Subject: login

Dr. Chow,
I am ready to go with my webpage, but am having difficulty changing by permissions. Perhaps I can see you briefly before class, or maybe after. Thank you,
Sid Rubey

Question related to Unix Basic Command and Tutorial

From: Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Tuesday, March 19, 2002 10:34 PM
To: 'Callahan Robert C CPT NORAD/USSPACECOM/J22X'
Cc: Edward Chow; CS522@cs.uccs.edu
Subject: RE: Help with UNIX commands

Bob,

It is rm.

http://www.emba.uvm.edu/CF/basic.html
There is one page summary at
http://www.nmsu.edu/~CandN/DOCS/UNIX/DOCS.Unix_commands.html

There is a Unix basic tutorial at
http://www.isu.edu/departments/comcom/unix/workshop/unixindex.html

Edward
UCCS CS Interim Graduate Advisor
=================================================
Professor Edward Chow Email: chow@cs.uccs.edu
University of Colorado at Colorado Springs http://cs.uccs.edu/~chow/
1420 Austin Bluffs Parkway TEL: (719)262-3110
Colorado Springs, CO 80933-7150 FAX: (719)262-3369

-----Original Message-----
From: Callahan Robert C CPT NORAD/USSPACECOM/J22X
[mailto:Robert.Callahan@PETERSON.af.mil]
Sent: Tuesday, March 19, 2002 12:00 PM
To: 'chow@cs.uccs.edu'
Subject: Help with UNIX commands

Professor,

What is the UNIX command used to delete a file? I tried 'del',
'delete',
'df', and a bunch of others. Since I don't have any training at all on
UNIX, I am shooting in the dark (and missing the intended target). It
would
be really helpful if I could get my hands on a list of basic UNIX
operating
commands. I am very familiar with DOS, but UNIX is enough different
that
I'm not having any luck with my DOS commands (except for 'cd').

Thanks for your help.

Bob Callahan

Question related to UCCS dialup (ISP) service, STP, ARP, DNS, SMTP, and PPP protocols:

From: C. Edward Chow [mailto:chow@cs.uccs.edu]
Sent: Thursday, August 29, 2002 12:03 AM
To: dbwilkin@netscape.net
Cc: Edward Chow; CS522@cs.ucc.edu
Subject: Re: a couple questions

David,

Here are short answers to your questions.

Edward

Quoting dbwilkin@netscape.net:

> Dr. Chow,
>
> I had a couple network-related questions:
>
> 1) Does UCCS offer ISP service for CS students? I have a CompuServe
> account but unfortunately it won't let me log on in Linux.

yes. there is dialup service for all UCCS students. The phone number is 5930109
See setup instruction at http://www.uccs.edu/~it/helpsheetsmenu/dial-up.htm
You need to apply for a computer service Unix/Email account that can be used
for dial up login. Apply at http://www.uccs.edu/cgi-bin/unac/index.html.

>
> 2) What is STP and ARP? Is DNS also a protocol?

STP: Spanning Tree Protocol. It is used by bridges of interconnected LANs to
exchange information and form a span tree relationship among them for
forwarding frames from LAN segment to another without looping.

ARP: Address Resolution Protocol. Since an Ethernet card (a Datalink layer
device) on each machine only read the frame header and not the IP address on
the frame payload, it only accepts frames with two kinds of destination
addresses in the frame header:

1. broadcast address with special 48 bit pattern (all ones).
2. the same burn in MAC 48 bit pattern (address) of the Ethernet card.

The sender needs to know the destination machine's ethernet 48 bit MAC to fill
in the frame header. ARP protocol is used by a network host to ask its
neighbors in the same LAN segment whether they own a particular IP address. The
sender sends a frame with broadcast address as destiation MAC address and frame
type as ARP. The frame payload contains an ARP packet. Every machine on the LAN
segment receives this Ethernet frame since it is a broadcast address. It
recognizes the frame type=ARP and sends the ARP packet to the ARP process on
the host machine for processing. ARP process will examine whether the IP
address is assigned to the Ethernet card during the network configuration step
of the machine.
If the IP address belongs to it, the machine will reply to the request machine
its 48 bit MAC (medium access control) (Ethernet Card) address. Once the
request machine receives the MAC address, it will save the association of the
IP and MAC addresses in a table (cache) for future use. All subsequent Ethernet
frames to be sent to the same IP address wil then be sent with frame containing
the same MAC address.

Yes. DNS (Domain Name System) is also a protocol. Every networked machine will
be configured to have 2-3 DNS servers for asking the IP address of a particular
DNS name (such as cs.uccs.edu). When receving a DNS packet with a domain name,
the DNS server will look up its table and reply with IP address. If there is
no entry there with the same DNS name, the DNS server will ask the root DNS
servers in the Internet for DNS server responsible for that domain, and then
get a DNS-IP mapping information back. The return entry will be cached in the
table for a certain period specified in the DNS configuration file.

>
> 3) What is the difference between SMTP and PPP protocols?

SMTP (simple mail transfer protocol). PPP (Point-to-Point Protocol).
SMTP is used for mail agents (servers) to exchange and deliver emails.
IMAP and POP3 protocol is for retrieving email from mail servers.
PPP is used by a dialup machine to negotiate the connection with a terminal
server including the authentication (login and password checking) and the
assignment of IP address by the terminal server to the dialup machine.

>
> Thank you very much for your help!
>
> David Wilkinson