1. Network Administration Homework1 Perl Programming Exercises

2. Analysis Ethereal Output (1)
A tool that can be used to analysis network traffic passed through your network interface

3. Analysis Ethereal Output (2)
Network Monitoring
Turn on the “promiscuous mode” of your NIC
Normal mode
NIC will collect those packets that destined to your computer
That is, destination IP = My IP / Broadcast IP
Otherwise, NIC will drop it.
Promiscuous mode
NIC will collect “all” packets
Turning on the promiscuous mode needs Root privilege
Tools that can do this:
tcpdump, ssldump, Ethereal

4. Analysis Ethereal Output (3)
To install ethereal, you can use this URL:
Download and execute it
To begin monitoring your network, you can:
Ctrl + K
Choose your interface
Specify filter
Man tcpdump
Ex:
Host
dst port 22
Check
Update list of packets in real time
Start capture

5. Analysis Ethereal Output (4)
After you have captured packets
Spend some time to investigate the content of each packet
Frame header
IP header
TCP/UDP header
Application data

6. Analysis Ethereal Output (5)
Purpose of this first exercise:
Learn how to use ethereal
Learn how to use ethereal to inspect TCP/IP that we have taught
Learn how to use Perl built-in function “pack” and “unpack”
Learn how to use Perl Curses::UI CPAN
Works you have to do in this exercise
Install and user ethereal
Install /usr/ports/devel/p5-Curses-UI
Spend some time to investigate packets content that you have captured
How TCP/IP headers looks like
Write a Perl script that satisfies those requirements in next slide

7. Analysis Ethereal Output (6)
Requirements of the first exercise
Input:
One Ethereal output
Output:
One curses window that lists packets found in Ethereal-output file
Each line represents one packet
Each line should have the following fields
SrcMac: Source MAC of that packet
DstMac: destination MAC of that packet
SrcIP: Source IP of that packet
DstIP: destination IP of that packet
SrcPort: source port of that packet
DstPort: destination port of that packet
Timestamp: the “captured” timestamp add by ethereal
List 10 lines at most in one window
Use “Curses:UI:ButtonBox” to list remain 10s’ packets
Like:
Provide “sort-by” functionality
Sorting by the above 7 fields

8. Supplement Information

9. Ethereal Output Format
One single Ethereal output file
24bytes-Ethereal-Header
Packets-with 16 bytes added information
4bytes time stamp (captured)
4bytes length of packet
4bytes actual packet length
4bytes timestamp (micro-)
4bytes Magic (0xa1b2c3d4)
2bytes major version number
2bytes minor version number
4bytes time zone offset
4bytes time stamp accuracy
4bytes snapshot length
4bytes Link-Layer Type (1)
4bytes time stamp (captured)
4bytes length of packet
4bytes actual packet length
4bytes timestamp (micro-)
Ethereal
Dump
Header
(24bytes)
4bytes time stamp (captured)
4bytes length of packet
4bytes actual packet length
4bytes timestamp (micro-)

10. CPAN (1) CPAN Search what you may like Install in your BSD
Comprehensive Perl Archive Network
Collection of Perl software modules that are developed and upload by Perl enthusiasts
Search what you may like
Install in your BSD
/usr/ports/devel/p5-* # /usr/ports/devel/p5-Curses-UI

11. CPAN (2) #!/usr/bin/perl use strict; use Curses::UI;
my $cui = new Curses::UI;
$cui->dialog("Hello, world\n");

12. CPAN (3) use strict; use Curses::UI;
my $cui = new Curses::UI(-color_support => 1);
my $mainWin = $cui->add(
undef, 'Window',
-border => 1,
-padtop => 1,
-padright => 2,
-padbottom => 1,
-padleft => 1,
-titlereverse => 0,
-title => 'My Main Window' );
my $settingViewer = $mainWin->add(
undef, 'TextViewer',
-padright => 1,
-padbottom => 10,
-focusable => 0,
-x => 1,
-y => 1,
-text => ‘這樣呢?'
$cui->dialog(‘test’);

13. CPAN (4) … sub sayhello $mainWin->add( { undef, 'Buttonbox',
-buttons => [ {
-label => "sayhello",
-shortcut => 1,
-onpress => \&sayhello },
-label => "saybye",
-shortcut => 2,
-onpress => \&saybye } ] );
sub sayhello {
$cui->dialog('Hello'); }
sub saybye
my $choice = $cui->dialog(
-message => 'Are you going to leave?',
-buttons => ['yes','no'] );
exit(0) if $choice;
$cui->mainloop();

14. CPAN (5)

15. pack and unpack (1) Usage Ex: pack TEMPLATE, LIST
Takes a LIST of values and
Converts it into a string using the rules
Ex:
$foo = pack("CCCC", 65, 66, 67, 68); // $foo = “ABCD”
$foo = pack("C4", 65, 66, 67, 68); // $foo = “ABCD”
($a, $b, $c, $d) = unpack(“CCCC”, $foo); // $a = 66
C means unsigned char value (c means signed)
4 means repeat 4 times

16. pack and unpack (2)
open (FD, "ethereal_example") || die "Can't open file:$!";
binmode(FD);
read(FD, $buffer, 24);
while( read(FD, $buffer, 12) != 0){
read(FD, $buffer, 4);
$length = unpack("l", $buffer);
read(FD, $buffer, 6);
$dstMAC = unpack("H*", $buffer);
$srcMAC = unpack("H*", $buffer);
printf("length is $length\n");
printf("dstMAC is $dstMAC, srcMAC is $srcMAC\n");
read(FD, $buffer, $length - 12); }
close(FD);
length is 74
dstMAC is 00d0b7177b07, srcMAC is 000fea86ddd0
dstMAC is 000fea86ddd0, srcMAC is 00d0b7177b07
length is 82
length is 202 …