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Bash script for ping in your own subnet


 
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# 1  
Power Bash script for ping in your own subnet

I have a question for one who wants to help me.

I want to create a bash script to ping IP-adresses. It must first ask me the beginnen IP, then the ending IP like: 192.168.100.1 - 192.168.100.255.
When nothing is filled in, then it must find my subnet and ping that, like when my ip is 192.168.100.6, it must ping from 192.168.100.1 - 192.168.100.255.

Yes I do have a script where the IP is already filled in, but not one, which knows in which subnet you are, to ping all of the IP adresses there...

How can I accomplish this?
Help is welcome!
# 2  
If you want to know your external IP, this is the simplest way:
Code:
IP="$(curl -s jackson.io/ip/)"

If you want to know your local IP, this should work:
Code:
DEV="$(netstat -nr | sed -n '/^0.0/s/.* //p')"
IP="$(/sbin/ifconfig $DEV 2>/dev/null | sed -n '/net /s/.*addr:\([0-9.]*\).*/\1/p')"

# 3  
netmask (utility of the Debian project) can be useful
Code:
~$ netmask -r 192.168.100.6/24
192.168.100.0-192.168.100.255 (256)

perts of the the man page:
Code:
SYNOPSIS
       netmask [ options ] spec [ spec ... ]
DESCRIPTION
       This  program  accepts and produces a variety of common network address and netmask formats.  Not only can it convert address and
       netmask notations, but it will optimize the masks to generate the smallest list of rules.  This is very handy if you've ever con‐
       figured  a  firewall  or  router and some nasty network administrator before you decided that base 10 numbers were good places to
       start and end groups of machines.

(...)

DEFINITIONS
       A spec is an address specification, it can look like:

address             One address.
address1:address2   All addresses from address1 to address2.
address1:+address2  All addresses from address1 to address1+address2.
address/mask        A group starting at address spanning mask.

       An address is an internet network address, it can look like:
ftp.gnu.org   An internet hostname.
209.81.8.252  A standard dotted quad internet address notation.
100           A decimal number (100 in this case).
0100          An octal number preceded by "0" (64 in this case).
0x100         A hexadecimal number preceded by "0x" (256 in this case).

       A mask is a network mask, it can look like:
255.255.224.0  A dotted quad netmask (netmask will complain if it is not a valid netmask).
0.0.31.255     A Cisco style inverse netmask (with the same checks).
8              The number of bits set to one from the left (CIDR notation).
010            The number of bits set to one from the left in octal.
0x10           The number of bits set to one from the left in hexadecimal.

AUTHOR
       netmask was written by Robert Stone.  Some algorithm design and optimization was provided by Tom  Lear.   This  manual  page  was
       written by Robert Stone.

# 4  
I use the script below to see my own IP from bash script:
Code:
#!/bin/bash
ifconfig | grep 'inet addr:' | grep -v '127.0.0.1' |
cut -d: -f2 | awk '{ print $1 }'

It will show your IP. If my IP is something like 192.168.1.5, it has to ping every addres in the 192.168.1.* segment.
This script must also ping every address when I am also in a different segment like 192.1.1.*

How can I accomplish that?

---------- Post updated at 06:55 AM ---------- Previous update was at 06:18 AM ----------

The above will only grep the whole ip. I want to grep 192.168.1.
Only the first 3 adresses. The last one will be filled in by a sequence {1..255}

The question is how to grep the first 3 numbers. now it is 192.168.1 but on a different subnet it could be something like 10.1.1.*

Last edited by Scott; 04-11-2011 at 08:52 AM.. Reason: Code tags
# 5  
You're assuming it's a 24-bit subnet. That's usually a good assumption with a local address like 192.168.x.x. But there's no reason it couldn't be a 16-bit or 26-bit or other size subnet (16-bit or larger for 192.168).

The Genmask column of the netstat -nr command output reveals the size of the netmask. A 24-bit subnet is shown as 255.255.255.0. A 27-bit subnet would be 255.255.255.224. Both are legitimate.

To answer your 3-number question:
Code:
IP=192.168.1.5
SUBNET=${IP%.*}
echo $SUBNET
192.168.1

# 6  
Here is my try, matching output for IP in all interfaces on machine.
Ping it once, if ping failes, print it (or do whatever you want there)

Code:
/inet addr:?[0-9]*.?[0-9]+\.[0-9]+\.[0-9]+/ {
gsub("(addr:|addr:127.0.0.1|.[0-9]*$)","",$2)
split($2,ipz,"\n")
	for ( i in ipz)
		for ( j=1; j <= 255; j++ )
		if (system("ping -c 1 " ipz[i]"."j ) != 0)
		print "ping FAILED on "ipz[i]"."j
}

Save this as pong.awk and run like
Code:
ifconfig | awk -f pong.awk

It will take a while ofcourse to 'scan' everything, if you have multiple interfaces in various subnets.
# 7  
Quote:
Originally Posted by KenJackson
You're assuming it's a 24-bit subnet. That's usually a good assumption with a local address like 192.168.x.x. But there's no reason it couldn't be a 16-bit or 26-bit or other size subnet (16-bit or larger for 192.168).
Yhat's why you can use the IP command to get information about address - mask, i.e:ip addr show eth0returns me
Code:
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 00:21:97:22:e8:4d brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.2/28 brd 192.168.0.15 scope global eth0

You can then tail/grep/sed/awk or what you can to get what you need (in this example, the mask has 28 bits).

You can also try ip route list which gives other useful information.

All those commands can be used to get info to ping the whole subnet.

Last edited by frans; 04-10-2011 at 02:53 PM.. Reason: added info aboute ip route

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