Get all connected IP´s on the Linux machine

Question

Recently i was asked a question in an interview which i couldn't do. Anyone got a solution for this?

Grab all connected IP´s on the Linux machine
check every connected IP if TCP port 1706 is open

if its open > execute command.  CURL ‘http:// some address ’ 
Else do nothing.
program will check this every 60 minits



Plattform Linux Ubuntu Server 12. X64 / x32

WAP in C++

Thanks!!

Answer 1

Make a bash script.

LOGIC:

Use netstat -natp (filter it through awk/sed to get the ports, then grep it) Then use a simple test to see if the result was empty. Run curl if it was.

Put this in a cron job. Simple stuff, really.

EDIT:

netstat is a utility which will show you all of the connections on your computer. netstat -natp shows a list of the programs which have tcp sockets on your computer.

sed and awk are used for text formatting. You can use them to list a specific column.

grep searches input to find a specified string.

bash allows for basic logic, and can be used to see if a string is empty.

cron is a linux process which schedules commands to be run at certain times.

EDIT #2:

You COULD poll /proc/net/tcp, but since netstat does that and formats it nicely, why bother?

Answer 2

In Linux, you look for files in /proc/net and parse that.

For example, TCP connections are listed in /proc/net/tcp

head /proc/net/tcp

will show something like this

  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode                                                     
   0: 00000000:0007 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 38148735 1 0000000000000000 100 0 0 10 -1                 
   1: 00000000:1F48 00000000:0000 0A 00000000:00000000 00:00000000 00000000   116        0 38923158 1 0000000000000000 100 0 0 10 -1                 
   2: 00000000:0CEA 00000000:0000 0A 00000000:00000000 00:00000000 00000000   120        0 12364094 1 0000000000000000 100 0 0 10 -1                 
   3: 0100007F:13AD 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1000        0 26454267 1 0000000000000000 100 0 0 10 -1                 
   4: 0100007F:008F 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 5570 1 0000000000000000 100 0 0 10 -1                     
   5: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 27328173 1 0000000000000000 100 0 0 10 -1                 
   6: 0100007F:1913 00000000:0000 0A 00000000:00000000 00:00000000 00000000   116        0 38923868 1 0000000000000000 100 0 0 10 -1                 
   7: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 18983193 1 0000000000000000 100 0 0 10 -1                 
   8: 0100007F:0277 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 38681424 1 0000000000000000 100 0 0 10 -1                 

You can then split the lines, look for the open connections and act accordingly. Look at thesource of netstat for more.