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libip_udp README
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Contents
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1. About libip_udp
2. Compilation
3. Testing
4. Usage
5. Provided Functions
6. Guarantee
7. Getting the Latest Version
8. Future Versions
9. Contact Information
10. References


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1. About libip_udp
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The students at the Vrije Universiteit Amsterdam who are in their 3rd year of
Computer Science must do computer networks practical work. They have to
implement TCP and HTTP on top of an IP library that is given on Minix.

Unfortunately, even though we respect Minix very much, development on that
operating systems means that we can't use our favorite editors and revision
control systems easily. Also, if we want to work at home, we need a native
install, a VMWare installation or a Bochs installation. All have their little
problems.

Therefore, we wrote this library, which emulates the CN IP library on Linux.
This is done by sending the IP packets over UDP on localhost.

In minix, the current ethernet device has to be specified by setting the ETH
environment variable. This works the same with libip_udp. The number is then
used to create the UDP port. For example, if ETH contains "1", the UDP port
will be 2809, if ETH contains "2" the UDP port will be 2810, etc. Currently,
up to 20 virtual ethernet devices can be created this way and they can all
send packets to eachother.

Virtual IP addresses are linked to virtual Ethernet devices using a very simple
scheme. Ethernet device 1 has IP 192.168.0.1, 2 has 192.168.0.2, etc.

Added benefits of using this library are:

- You can use the GNU Debugger
- (see Future Versions)


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2. Compilation
--------------

Provided that you have the GNU C Compiler, just do:

$ make
$ cd origtest
$ make


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3. Testing
----------

Once compiled, you can test the library by running the client and server
programs in the "origtest" directory. These are directly taken from the CN IP
library. Open two terminals. First, start the server in one of them:

$ export ETH=2
$ ./server

Then, start the client in the other:

$ export ETH=1
$ ./client

The client should now have sent a packet and the server should have received
one.


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4. Usage
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The computer networks practicum tells you to make directory structure that
looks like this:

cn
|-ip
|-tcp
|-http
|-test

Simply rename the ip directory to something else and then put a symlink to
libip_udp in its place:

$ cd cn
$ mv ip ip_orig
$ ln -s <path-to-libip_udp> ip

Now you can use it like you would under Minix according to the CN practicum
instructions. Keep in mind that the virtual IP addresses are 192.168.0.1,
192.168.0.2, etc. Make sure your IP<x> environment variables and/or the
#define statements in your code are set accordingly.

You can specify the virtual reliability of libip_udp with the PACKET_LOSS
environment variable. Set it to a number between 0 and 100 that specifies
the percentage of packets to be dropped.

It is possible to connect two programs using libip_udp via the Internet or
a LAN. To do this, set the REAL_PEER_IPADDR environment variable to the
other side's IP address. If there is a firewall, make sure the appropriate
UDP port is open (2809+ETH-1).

The same is possible for the logger. The variable is named REAL_LOG_IPADDR.


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5. Provided Functions
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The libip_udp library provides the following functions:

- ip_init()
- ip_send()
- ip_receive()
- inet_checksum()
- inet_aton(), inet_ntoa()
- signal()

Also the following types can be used:

- iphdr_t (do not use directly! only for sizeof())
- ipaddr_t
- u8_t, u16_t, u32_t

Of course, standard UNIX functions like printf(), malloc() and free() can also
be used because they are defined in POSIX.


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6. Guarantee
------------

This library is provided solely as an aid for doing the computer networks
practicum. We, the authors, give no guarantee whatsoever that code developed
using this library will work perfectly under Minix. Also, we have no
affiliation (except being students) with the people of the CN practicum.

MAKE SURE that your code works fine in the Minix environment before submitting
it.

Please mail us about any problems you encounter so we can fix them.


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7. Getting the Latest Version
-----------------------------

The latest release can be found on the website (see Contact Information). If
you want to keep up to date on the development, you may clone the latest
development revision from Git:

$ git clone git://github.com/mklencke/libip_udp.git

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8. Future Versions
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We are working on some new features for future version:

- Solaris and BSD Support
- Packet insertion. A tool to insert extra packets that have nothing to do
  with the current TCP connection. Your TCP library must be able to handle
  this.


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9. Contact Information
----------------------

libip_udp is being developed by Marten Klencke <[email protected]> and
Erik Bosman <[email protected]>.

Website  : http://www.cs.vu.nl/~mklencke/libip_udp.php
E-Mail   : [email protected]


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10. References
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- http://www.cs.vu.nl/~cn/
- http://www.cs.vu.nl/
- http://www.cs.vu.nl/~ast/minix.html
- http://www.vmware.com/
- http://bochs.sourceforge.net/