CSCI 251 - Lab5

CSCI 251 Systems and Networks

Lab 5 – Accessing the Internet from your vbx and Vice Versa

Friday, February 10, 2010

Note: The assignment is to be completed by the end of the lab session.

Discussion

Introductory Comments

You have already accessed the outside Internet by using the Debian package management tools i.e. aptitude and synaptic. But in this assignment you will use more typical user tools such as

ssh (secure shell) and sftp (secure file transfer protocol)
a web browser

You'll find that, as installed, your vbx can reach the outside Internet with those tools. Note that the interaction with the outside Internet will be initiated from within the vbx.

The reverse is not true by default. You cannot reach the vbx by attempting to initiate the contact from the outside Internet. In this assignment, we will change this default behavior. As a practical example, we'll focus on building a web site within the vbx that can be accessed from outside your machine.

[Note: the location of a machine's default web site and those of its default web sites for individual users are not necessarily universal. We'll follow the Debian conventions. However, we'll also see the configuration file where such defaults are established, information which is applicable to other distributions.]

Instructions

Before starting the various tasks comprising this assignment

logon to your assigned machine
then start up you virtualized guest system, vbx

We'll eventaully need an ssh server on your vbx, so at your vbx command line, as root, enter

aptitude install openssh-server

The tasks described below are to be performed on your host system or your vbx as specified in each case.

Task #1: sftp to the outside Internet

Here, as a review, you will repeat part of Task #1 from Lab 3 - except that we'll use sftp instead of ssh. Contact your host machine from your vbx. Do you recall how to find the address of your host system? Find out by using a terminal window on host OS and enter

/sbin/ifconfig eth0

and find what it says for the inet addr of that interface. Represent that by xxx.xxx.xxx.xxx.

1.1 Now try to establish an sftp connection with your host machine from the vbx screen via

sftp <your_host_username>@xxx.xxx.xxx.xxx

for example, using a fictitious username and IP address:

ssh schwartzd@192.168.0.205

Then transfer a file from your vbx to your host system. Record the result: Was it as expected? Explain.

1.2 By now you should have an account on csciun1, try to sftp into that from your vbx screen e.g.

sftp schwartzd@csciun1.mala.bc.ca

Then transfer a file from your host system to your vbx. Record the result: Was it as expected? Explain.

[Note that the prior two subsections illustrate the ability to transfer files into or out of your vbx, a useful option.]

1.3 Get together with one of the other lab students and see if you can ssh into your vbx from that student's vbx.

Record the result: Was it as expected? Explain.

1.4 Try to ssh into your vbx from your csciun1 account.

Record the result: Was it as expected? Explain.

Task #2: Use the vbx's browser to contact various web sites

If you have not yet installed a browser on vbx, enter

aptitude install iceweasel

[Note that iceweasel is a fork of firefox, arising from a debate over parts of firefox considered non-free. The iceweasel package uses only free components e.g. artwork and plugins.]

2.1 Use the vbx browser to contact some well known external site e.g. Google.

Were you successful?

2.2 Let's determine whether your vbx has a default web site.

Ultimately, we would like web sites on the vbx. So we begin by seeing if one is already there.

To find out, use the vbx browser to contact the url for your vbx, known to vbx as

http://127.0.0.1

or, equivalently,

http://localhost

If this fails, it is likely that no default web site is present, nor the underlying web server.
[Note that this will be the case, unless you installed a web server on your own.]

To choose a web server, Start synaptic and do a search on web server. Of course, you'll get back all sorts of information. Certainly, you'll see references to apache2, the current king of web servers. You'll also see another named boa. Find the number of bytes required

to download apache2 (but don't actually download it)
to download boa (but don't actually download it)

Ask your instructor to show you how to determine these download sizes. Record those numbers for the Demonstration (later). Let's continue our quest for small packages and choose the smaller, that is, the boa web server, using synaptic.

Once it's installed, look at its man page to see how its design philosophy differs from that of apache2.

Again attempt to contact the default web site of your vbx by trying

http://127.0.0.1

or, equivalently,

http://localhost

There should now be a default web site on your vbx. But where is it? We'd like to replace it with our own. There are various ways to do the detective work required to find where the default web site is. For example,

we know that /etc often contains configuration information; is there a directory /etc/boa/ with useful information?
does the default web site itself contain any clues (not always, but sometimes)

Find the location of the default vbx web site and create your own index.html file. Demonstrate that it works by browsing to

http://127.0.0.1

or, equivalently,

http://localhost

2.3 Does your vbx have a web site support for individual users?

The web site at

http://127.0.0.1

or, equivalently,

http://localhost

is for the vbx itself and requires root access in order to make changes. But we hope that there would be some sort of built in support allowing individual users to have their own web sites. For example, on csciun1, my web site is at

http://csciun1.mala.bc.ca/~jayeward

So, if your vbx username is, say, schwartzd, you might expect to find a web site on your vbx at

http://127.0.0.1/~schwartzd/

Try this with your vbx username. You'll likely get the dreaded 404 Not Found message. Nevertheles, it doesn't take much work to implement this:

figure out what to do
then make your own index.html file
access it as discussed above

[Hint: Start by looking through /etc/boa/boa.conf for ideas.]

2.4 Backup your individual user website and transmit the backup file to your csciun1 account

Once you have successfully completed the prior section, tar and gzip the directory containing your individual user website. Then copy that backup file to your csciun1 account using sftp.
[Note: if the required shell commands aren't familiar, request help from your instructor.]

Obviously, the amount of material being backed up is trivial. But in a more realistic setting where you are developing a complex web site, you will want to make frequent onsite and offsite backups ... for both the current web site and its previous version.

2.5 Try to access your vbx web site using the browser in some other student's vbx

Now try to access your vbx web site using the browser in some other student's vbx, by using the url

http:<your_host_IP_address>/

Record the result: Was it as expected? Explain.

Then try

http:<your_host_IP_address>:8080/

Record the result: Was it as expected? Explain.
[Note: The 8080 will make more sense after Task #4 is completed.]

Task #3: Use Port Forwarding so you can ssh (or sftp) to your vbx from the outside Internet

In Tasks #1 and #2, you hopefully determined that you can ssh or sftp out from vbx, but not in. This follows from the fact that, by default, virtualbox uses NAT (Network Address Translation). In effect, each packet sent from vbx is modified so that it appears to have come from the host machine. But part of the outgoing payload is the ID of vbx as the originator. The outside receiver responds to the host machine, but the responding message also includes the vbx ID. The host OS knows to route that to vbx because of that ID. However, if an outside agent initiates the contact, the vbx ID is not present and the host system keeps that message for itself. Port forwarding is one way to solve this problem. You'll first apply this to ssh.

Now ssh, by default, uses port 22. You'll leave that as is, so any 'normal' ssh activity will still be received by the host OS and kept as its own. But you'll assign a new port number for ssh attempts intended for the vbx. As the new port number, use 2222 (must be greater than 1024, lower numbers require root privileges). Thus if an outside agent contacts the host IP address via ssh, but specifies port 2222, your host system will forward this to your vbx. Virtualbox provides a high level tool. To set this up, using a host console window, enter the 3 commands listed below (you might put all 3 into an executable script, if your typing isn't fast and accurate):

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort" 2222

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort" 22

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol" TCP

Next, close your vbx with the "Save the machine state option". Then restart from the virtualbox interface, as usual. Then try it out as follows:

from the host system:

ssh
-l <your_vbx_username> -p 2222 localhost or ssh
-l <your_vbx_username> -p 2222
<host-IP-address>

from you csciun1 account

ssh -l <your_vbx_username> -p 2222 <host-IP-address>

Record the results from the above ssh activities: Were the results as expected? Explain.

Task #4: Use Port Forwarding so you can contact your vbx with a browser from the outside Internet

This is the same solution as for ssh/sftp, except applied to http. The default port for http is 80. So to set this up, enter the 3 commands listed below (as before, you might put all 3 into an executable script, if your typing isn't fast and accurate):

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/boa/HostPort" 8080

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/boa/GuestPort" 80

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/boa/Protocol" TCP

Next, close your vbx with the "Save the machine state option". Then restart from the virtualbox interface, as usual.

Then try it out by

using the browser in the host system,

contact

http://127.0.0.1/

then

http://127.0.0.1:8080/

then try those both again using the IP address of the host machine instead of 127.0.0.1

using the browser in the vbx of one of the other students to contact your host'e web site using the IP address of your host

using the browser in the vbx of one of the other students to contact your vbx web site using the IP address of your host with the appended :8080

Record the results from the above browser activities: Were the results as expected? Explain.

Task #5: Verifying and Clearing Port Forwarding Settings

There is a command to verify your current port settings:

VBoxManage getextradata vbx enumerate

You can also clear the settings, returning them to defaults. For example, to clear the ssh settings, use:

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort"

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort"

VBoxManage setextradata vbx "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol"

Task #6: Demonstration

Before you leave for the day, ask the instructor to stop by and

look at the results you recorded (with explanations)
check your system for compliance with this assignment.

Once finished, ensure that the instructor enters that fact in his record book.