Network Admin Stuff: July 2016

Sunday, July 24, 2016

Cisco: Beginner Level

Main Page | CCNA Exercises | CCNP Labs
Hacking | KidsPlayPython

How to install and Use IOS on Linux.

Mostly Harmless Weekend Hacking
with Raspberry PI and Kali Linux

'Hello World' Under the Hood (new!)
Ping Used as an OS Fingerprinting Tool
Passive Reconnaissance - Flowers in Corp Web Page
Whois?
Diving into Bash
Cheap Hacker's Lab
Raspberry PI Installation.

CCNA Packet Tracer Labs:

IOU Forbidden Fruit

How to install and Use IOS on Linux.

Disclaimer!
This is a personal weblog. The opinions expressed here represent my own and not those of my employer. Also the stupidity is mine and mine alone. Some post content might be rude, offensive or borderline obnoxious (anything marked with label 'Ranting' is not suitable for people under 18 years old). Since, I try to have an open mind you can expect that my opinions may and probably will change in time. You may leave some comments but I reserve the right to ignore them completely.

The technical content of this blog is a product of weekend/sleepless-and-or-hotel night/after-work technical struggle. Despite all efforts, it may be inaccurate and reflects the author's knowledge as of the time of writing the posts. The author of the posts will not assume any liability or responsibility to any person or entity with respect to loss or damages incurred from information contained in this blog. Any resemblance to some other training materials and/or CCNA/CCNP/CCIE exams is completely coincidental.

Hacking

Mostly Harmless Weekend Hacking
with Raspberry PI and Kali Linux

1. Raspberry PI Installation.
2. Cheap Hacker's Lab.
3. Diving into Bash.
4. WHOIS?
5. Passive Reconnaissance - Flowers in Corp Web Page.
6. Ping Used as an OS Fingerprinting Tool.
7. 'Hello World' Under the Hood.

Hello World under the Hood

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A simple code everybody starts with is a “hello world!” program. Here, using the ‘for’ loop, I make my computer display hello twice. Looking at the code it is easy to figure out what it does.

But it is not exactly how hackers look at it. There is some magic happening there.

What do computers really do? They obediently follow the program (step by step defined recipe). The same way we humans do things. Listen to master’s orders.
But the difference is that they can do the same thing over and over again without breaking sweat (loops) and without being bored don’t complain because they are machines. Dumb without a program, but boy are they fast if you provide a program to run!
But how do they do that? What’s under the hood.

#include 

int main(void) {

    int i;
    for (i = 0; i < 2; ++i) 
        printf("Hello, world!\n");    

    return 0;
}

The source code (like the one above) is set of instructions that must be translated (compiled) into a machine language that the CPU understands. All instructions are in fact strings of ones and zeros. Those form something called machine code. CPU can decode them as instructions and compute stuff, which means they operate on data.
Here is what my first program does.

A look into Computer Guts

Compile and run the code. See what it does.

pi@tron:~/dh $ gcc -g -o hello hello.c 
pi@tron:~/dh $ 
pi@tron:~/dh $ ./hello
Hello, world!
Hello, world!
pi@tron:~/dh $

Compilation -g allows gdb to read the code and step through it.
Inside the computer the code operates at a different level.
First GDB lesson courtesy of beej.us and few other places on the net.
My first program up close looks like this:

$ objdump -M intel -D hello | grep -A20 main.:
000000000040052d :
  40052d: 55                    push   rbp
  40052e: 48 89 e5              mov    rbp,rsp
  400531: 48 83 ec 10           sub    rsp,0x10
  400535: c7 45 fc 00 00 00 00  mov    DWORD PTR [rbp-0x4],0x0
  40053c: eb 0e                 jmp    40054c 
  40053e: bf e4 05 40 00        mov    edi,0x4005e4
  400543: e8 c8 fe ff ff        call   400410 
  400548: 83 45 fc 01           add    DWORD PTR [rbp-0x4],0x1
  40054c: 83 7d fc 01           cmp    DWORD PTR [rbp-0x4],0x1
  400550: 7e ec                 jle    40053e 
  400552: b8 00 00 00 00        mov    eax,0x0
  400557: c9                    leave  
  400558: c3                    ret    
  400559: 0f 1f 80 00 00 00 00  nop    DWORD PTR [rax+0x0]

0000000000400560 :
  400560: 41 57                 push   r15
  400562: 41 89 ff              mov    r15d,edi
  400565: 41 56                 push   r14
  400567: 49 89 f6              mov    r14,rsi

It is beautiful. Looking at the code like that.
I want gdb to debug code using Intel representation rather than default AT&T. Here’s my file that is going to take care of it:

$ cat ~/.gdbinit 
set disassembly intel

CPU registers are sort of like quick access variables. Here they are:

$ gdb -q hello
Reading symbols from hello...done.
(gdb) break main
Breakpoint 1 at 0x400535: file hello.c, line 6.
(gdb) run
Starting program: /home/jaro/Desktop/Jun-Dec-2016/14.Code/aoh/hello 

Breakpoint 1, main () at hello.c:6
6     for(i = 0; i < 2; ++i)
(gdb) info registers
rax            0x40052d 4195629
rbx            0x0 0
rcx            0x0 0
rdx            0x7fffffffe178 140737488347512
rsi            0x7fffffffe168 140737488347496
rdi            0x1 1
rbp            0x7fffffffe080 0x7fffffffe080
rsp            0x7fffffffe070 0x7fffffffe070
r8             0x7ffff7dd4e80 140737351863936
r9             0x7ffff7dea530 140737351951664
r10            0x7fffffffdf10 140737488346896
r11            0x7ffff7a36e50 140737348070992
r12            0x400440 4195392
r13            0x7fffffffe160 140737488347488
r14            0x0 0
r15            0x0 0
rip            0x400535 0x400535 
eflags         0x202 [ IF ]
cs             0x33 51
ss             0x2b 43
ds             0x0 0
es             0x0 0
fs             0x0 0
gs             0x0 0
(gdb)

Program listed in gdb:

(gdb) list
1 #include 
2 
3 int main(void) {
4 
5     int i;
6     for(i = 0; i < 2; ++i)
7         printf("hello, world.\n");
8 
9     return 0;
10 }
(gdb)

Now time to disassemble the code:

(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
=> 0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

The arrow points to the firs instruction to be executed as per address in rip (program counter register). The command x is for examine.

(gdb) info register rip
rip            0x400535 0x400535 
(gdb)

Funny thing is that I am no programmer. Not at all. I am just starting. But I do know the music when I hear one. Just like this one below:
Move value 0 to the memory location (here in hex) minus 4 bytes.

=> 0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

And next instruction (nexti). Once executed it will jump to the memory location: 0x40054c where the next command must be executed. The rip register (instruction pointer is always incremented to point to the next instruction.

(gdb) nexti
0x000000000040053c 6     for(i = 0; i < 2; ++i)
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
=> 0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

Here we go. Jump baby, jump!

(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
=> 0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

Is the value what variable i points to still lower than 2 (our loop condition)? Next instruction jle says: if less or equal/not greater. It relies on flags: SF<>OF or ZF == 1.
Let’s see those CPU flags after we executed comparison. Here SF is set but there is no OF (not set) if I understand it correctly.

(gdb) nexti
0x0000000000400550 6     for(i = 0; i < 2; ++i)
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
=> 0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb) info register eflags
eflags         0x297 [ CF PF AF SF IF ]
(gdb)

Jumping to the location pointed then!

(gdb) nexti
7         printf("hello, world.\n");
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
=> 0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

What is at this location? String to be printed of course. It is placed into Destination Index (EDI) register.
Let’s read what is at the location 0x4005e4. The gdb instruction x/12x means: examine 12 bytes in hex at the location (here: 0x4005e4).

(gdb) x/12x 0x4005e4
0x4005e4: 0x68 0x65 0x6c 0x6c 0x6f 0x2c 0x20 0x77
0x4005ec: 0x6f 0x72 0x6c 0x64
(gdb)

Hex 0x68 is lower case ‘h’, 0x65 is lower case ‘e’ etc. It gets ready to be used by C standard library function printf(). Calling the function and magic happens.

(gdb) nexti
0x0000000000400543 7         printf("hello, world.\n");
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
=> 0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

Go baby! Display it! Procedure Linkage Table (PLT) locates the library code to use (libc.so.x).
Next instruction goes back to for loop and adds 1 to variable i.

(gdb) nexti
hello, world.
6     for(i = 0; i < 2; ++i)
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
=> 0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

Now the variable i is 1 (0 + 1) so the same process is repeated. In order to jump out of the loop the variable i must not be less than 2. One more loop and we finish the job.

=> 0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb) info register eflags
eflags         0x202 [ IF ]
(gdb)

Now, neither SF<>OF or ZF == 1 are seem to show to be the case. We do NOT jump but follow to the next instruction that puts value 0 into the accumulator register.

(gdb) nexti
9     return 0;
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
=> 0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

We clean stuff up (exit status 0 is success I guess). And we leave the party and return to operating system.

(gdb) nexti
10 }
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
=> 0x0000000000400557 <+42>: leave  
   0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb) nexti
0x0000000000400558 10 }
(gdb) disassemble main
Dump of assembler code for function main:
   0x000000000040052d <+0>: push   rbp
   0x000000000040052e <+1>: mov    rbp,rsp
   0x0000000000400531 <+4>: sub    rsp,0x10
   0x0000000000400535 <+8>: mov    DWORD PTR [rbp-0x4],0x0
   0x000000000040053c <+15>: jmp    0x40054c 
   0x000000000040053e <+17>: mov    edi,0x4005e4
   0x0000000000400543 <+22>: call   0x400410 
   0x0000000000400548 <+27>: add    DWORD PTR [rbp-0x4],0x1
   0x000000000040054c <+31>: cmp    DWORD PTR [rbp-0x4],0x1
   0x0000000000400550 <+35>: jle    0x40053e 
   0x0000000000400552 <+37>: mov    eax,0x0
   0x0000000000400557 <+42>: leave  
=> 0x0000000000400558 <+43>: ret    
End of assembler dump.
(gdb)

Music's over and it's midnight on Saturday. Time to go to bed.

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Saturday, July 16, 2016

Ping as an OS Fingerprinting Tool

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What does PING utility do?
It sends an ICMP 'echo message' (type 8) and if firewalls don't block it, the sender gets ICMP 'echo reply' (type 0) back. If it works we can get an estimate round-trip time of a target host and we will know it's alive!

But there is more to it than that ;-)

Using ping utility venture a guess of what operating system it runs (Windows, Linux, or IOS).

Let's look at this ping results:

pi@tron:~ $ ping -c3 -n www.cisco.com
PING e144.dscb.akamaiedge.net (23.200.96.126) 56(84) bytes of data.
64 bytes from 23.200.96.126: icmp_seq=1 ttl=58 time=5.64 ms
64 bytes from 23.200.96.126: icmp_seq=2 ttl=58 time=7.03 ms
64 bytes from 23.200.96.126: icmp_seq=3 ttl=58 time=5.50 ms

Based on this output we can venture a guess regarding OS of target and how many routers away it is! The 'tell' is the TTL value of the responder.

We know that the default values of TTL are as follows:

MS Windows: TTL = 128.
Linux: TTL = 64.
Cisco IOS: TTL = 255.

Based on the above output I think www.cisco.com most likely runs on Linux system. It is also 6 hops (routers) away from my Raspberry PI computer. Systems on the Internet are rarely farther than 20 hops. So, if we assume that it is Linux, it uses the TTL value of 64, Response comes with ttl=58. That would be six hops away.

Let's verify that last fact using traceroute (if not installed use: apt-get install traceroute).

ppi@tron:~ $ traceroute -n www.cisco.com
traceroute to www.cisco.com (23.200.96.126), 30 hops max, 60 byte packets
 1  192.168.0.1  0.623 ms  0.726 ms  0.767 ms
 2  193.95.131.7  5.557 ms  5.915 ms  5.829 ms
 3  193.95.138.1  6.519 ms  6.548 ms  6.462 ms
 4  193.95.129.100  6.477 ms 193.95.129.104  6.577 ms 193.95.129.100  6.791 ms
 5  193.95.129.127  6.804 ms  6.975 ms  6.889 ms
 6  193.242.111.55  8.546 ms  8.142 ms  8.046 ms
 7  23.200.96.126  6.145 ms  5.620 ms  5.577 ms
pi@tron:~ $

Six routers and the seventh number is the target host.

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Wednesday, July 13, 2016

Passive Reconnaissance - Flowers in Corp Web Page

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This week could not be busier so in order to relax this evening another small problem. All towards ultimate goal: hacking systems like a pro ;).

Find a few Cisco servers that could be out target for ... hmm... closer inspection, should we choose learn about their vulnerabilities

How about we try to look at in the company's web page?
Can we find any interesting target IP addresses there?

Raspberry PI to the rescue!

First let's create a working directory and download the index.html page:

pi@clu:~ $ mkdir playground
pi@clu:~ $ cd playground
pi@clu:~/playground $ wget www.cisco.com
--2016-07-13 21:37:53--  http://www.cisco.com/
Resolving www.cisco.com (www.cisco.com)... 23.38.210.91, 2a02:26f0:71:185::90, 2a02:26f0:71:18d::90
Connecting to www.cisco.com (www.cisco.com)|23.38.210.91|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘index.html’

index.html                                  [ <=> ]  66.06K  --.-KB/s   in 0.005s 

2016-07-13 21:37:53 (12.5 MB/s) - ‘index.html’ saved [67641]

pi@clu:~/playground $

Okay. Let's search for hyperlinks inside html code. See what we can find.

grep "href=" index.html

WOW! The output is huge! Calling 'cut' for help now.

I am going to match on slash (/) as a delimiting character (-d). Third field (-f3) is going to extract links. Hopefully...

pi@clu:~/playground $ grep "href=" index.html | cut -d "/" -f3

It is beginning to shape up a bit. But the output still has lines of text that are not DNS names. Another grep matching on a dot should clean the output (to match on a dot character it must be escaped with a backslash).

pi@clu:~/playground $ grep "href=" index.html | cut -d "/" -f3 | grep "\."

There is still some text I don't need. A few DNS names are followed by double quote and characters. Another 'cut' will fix it. Also it would be good idea to get rid of the duplicate names and save the whole "discovery" to file 'links.txt'.

pi@clu:~/playground $ grep "href=" index.html | cut -d "/" -f3 | grep "\." | cut -d '"' -f1 | sort -u > links.txt 
pi@clu:~/playground $

Reading the content...

pi@clu:~/playground $ cat links.txt

Sweet!
Now, just for fun, a bash 'for loop' will convert those into IP addresses. That's thanks to 'host' utility that comes with every Linux.

pi@clu:~/playground $ for url in $(cat links.txt); do host $url | grep "has address" | cut -d " " -f4; done > ip.txt
pi@clu:~/playground $ cat ip.txt

Who would think that so many corporate server IPs can be found on the main page?

And that is just a beginning of our fun!

Now, after this quick mental exercise I feel a bit more relaxed. I will be able to face tomorrow. And tough meeting with the suits I am NOT looking forward to.

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Sunday, July 10, 2016

Diving into Linux Bash

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Linux operating system has everything any hacker needs. Bash with all the tools that can be combined to create beautiful pyramid of fast actions will be the core of this blog. Let's log on to Raspberry PI and begin the adventure.

Send 10 ping packets to www.cisco.com. Using bash tools extract the slowest and fastest response.

Ping uses ICMP echo (type 8) and echo reply (type 0) messages. As long as firewall between the sender and the receiver do not block those messages, using ping utility we can check if the target system is alive (at least at the layer 3 of OSI model).

First how to send just 10 ping packets using Linux Bash?

pi@tron:~ $ ping -c10 www.cisco.com > ping.txt

Linux sends ping until you stop it with CTRL-C. In order to send a number of ping packets option -c (count) followed by number 10 will send only 10 packets. Then it stops.

The result of the ping is going to be sent to a file called 'ping.txt'

Let's see the results:

pi@tron:~ $ cat ping.txt

The output is nicely placed in columns separated by a 'space' character. There are 9 columns of output. This can be used to our advantage.

First I am going to get rid of the output that does NOT have 'ms' leaving only what I want:

pi@tron:~ $ grep "ms" ping.txt

Then, using 'awk' utility I will print out the last two columns (awk breaks each line into variables $1 = 64, $2 = bytes $3 = from, etc.).

pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}'

There is some garbage left at the end of the output now. So, let's get rid of it:

pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}' | grep "ms"

Now, I am only interested in displaying the number and ms:

pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}' | grep "ms" | cut -d "=" -f2

Sort them from lowest to highest delay:

pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}' | grep "ms" | cut -d "=" -f2 | sort -n

And finally using 'head -1', display the lowest delay value and 'tail -1' display the highest delay value:

pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}' | grep "ms" | cut -d "=" -f2 | sort -n | head -1
5.30 ms
pi@tron:~ $ grep "ms" ping.txt | awk '{ print $8,$9}' | grep "ms" | cut -d "=" -f2 | sort -n | tail -1
5.68 ms
pi@tron:~ $

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Cheap Hacker's Lab

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If you want to play the piano, you must get yourself a piano.

It is fun to learn Cisco stuff but without access to their proprietary toys, you can learn the basics but you can't become a virtuoso, can you?

So what's the alternative for my restless mind?

OPEN SOURCE SYSTEMS BABY!

Quick assessment of the situation:

I have two Raspberry PI computers running Raspbian OS, and a salvaged old Dell Optiplex 745 tower that was being decommissioned and doomed to be scrapped. It has 4 GB of RAM memory and 80GB HD. It's enough to install ... KALI LINUX.

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Raspberry PI Installation

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Download the Linux image for Raspberry Pi (I use Raspbian)

Image Download

Then follow the installation instructions:

Windows users
Click here for Installation instructions

Linux Users
Click here for installation instructions

Since I use Linux to image the SD card, so this is what it is going to look like:

1. Checksum check if the file is intact.

$ sha1sum 2015-05-05-raspbian-wheezy.zip

$ cb799af077930ff7cbcfaa251b4c6e25b11483de

Compared with the number on 'download' page and the digest value is the same.

2. Check how my system detects sd card.

First 'df -h' without sd card installed

Output without SD Card

Then insert sd card and repeat the same command:

Output with SD Card Inserted

My system mounts sd card as: /dev/mmcblk0p1.

3. Unzip the image downloaded:

$ unzip 2015-05-05-raspbian-wheezy.zip

4. Unmount sd card

$ umount /media/jaro/D681-1D95

5. Using 'dd' copy the image onto the sd card (make sure you use the whole partition of the card - here: /dev/mmcblk0)

$ sudo dd bs=4M if=2015-05-05-raspbian-wheezy.img of=/dev/mmcblk0

It will take a while to copy image and nothing shows on the screen during that time. Just give it a time.

6. Insert sd card into Raspberry PI and connect to your TV set.

Once my Raspberry PI is hooked up to the TV set

A tool called 'raspi-config' is the first thing that is greeting me. It can be invoked at any point from CLI (command line interface) using the following command:

$ sudo raspi-config

all information on raspi-config can be found at: http://elinux.org/RPi_raspi-config

Avoiding too much deliberation I arrive with the following settings:

Option 1: Expand Filesystem

This allows system to see and use the whole SD Card.

Option 2: Change User Password.

I have changed default password (defaults: user=pi, password=rasbberry)

Option 3: Enable Boot to Desktop/Scratch

Console Text console, requiring login (default)

In case I wanted Graphical User Interface (GUI) I can always type:

$ startx

Graphical User Interface is pretty and makes simple task simple. But my goal is to discover the full power of this little computer and Linux. This is why I will be using SHELL most of the time.

Option 8: Advanced Options

A3: Memory Split

(How much memory should the GPU have)? 32

Since I don't use GUI, 32 MB should do.

A4: SSH (in order to be able to log on to PI from other computers (putty etc.)

If I don't like them I can change them anytime I want by invoking the tool again.

The last thing I want to do is to make sure that IP address of my Raspberry PI has a static IP address rather than using DHCP server. It will make my ssh access much easier later.

I edit the file in which system keeps the information about IP settings (I'm choosing IP address that is not part of DHCP in my network (A.B.C.D are values used in my home network):

$ sudo nano /etc/network/interfaces

iface eth0 inet static

address A.B.C.D

netmask 255.255.255.0

network A.B.C.0

broadcast A.B.C.255

gateway A.B.C.254

Content saved with CTRL-x / save
(Note: learn VIM text editor. It's usage is more difficult but gives more power as well).

And...

IT'S ALIVE

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