Installation

Module Dependencies

argparse (if Python version is <= 2.6)
netattr
netifaces

Note

As long as your setuptools installation is reasonably up to date, setup.py will take care of installing any required dependencies.

1. Clone the cidrchk git repository

git clone https://github.com/jhunkeler/cidrchk.git

2. Install the script

cd cidrchk
sudo python setup.py install

If you are unable to install cidrchk as root, please use the following notation instead:

python setup.py install --user

What is cidrchk?

cidrchk is a simple Python script with only one purpose: To inform a user whether or not their computer is connected to a particular network.

How do I use it?

Let's assume you depend on autofs to automatically mount NFS directories at-will.

However, when you are off-site or not connected to your institution's VPN, you quickly realize attempting to access these data areas causes significant delays (i.e. a five minute default timeout)

Consider the following .cshrc example:

setenv PATH ${HOME}/bin:${PATH}
setenv MYDATA /remote/data1
alias badidea "cd ${MYDATA}"

What happens if you attempt to execute your favorite alias?

$ badidea
[ no output, waiting for autofs to timeout ]

Whoops! Things didn't go as planned, so let's take a look at the same .cshrc example using cidrchk:

setenv PATH ${HOME}/bin:${PATH}
setenv MYDATA /remote/data1

set _OFFSITE = `cidrchk 10.0.0.0/20 66.55.32.0/20 >/dev/null`
setenv OFFSITE ${status}
unset _OFFSITE

alias badidea "cd ${MYDATA}"

if ( ${OFFSITE} ) then
    unalias badidea
endif

In the above example the following is true:

If 10.0.0.0/20 represents your institution's VPN address space and 66.55.32.0/20 represents your company's local intranet, and your home IP was 192.168.1.101, cidrchk returned a non-zero value indicating your computer was "off-site".

Furthermore, if your computer's IP address was 66.55.45.10 (i.e. you are in your cubicle), cidrchk would return zero indicating your computer was "on-site".

Other Possibilities

Issuing -v to cidrchk will echo the return value to the console, resulting in slightly cleaner code:

setenv OFFSITE `cidrchk -v 10.0.0.0/20 66.55.32.0/20`

if ( ${OFFSITE} ) then
    # do something clever to prevent personal hardship
endif

The downside to parsing a string rather than an integer is logical operators will not work as expected. ${OFFSITE} > "0" is not the same as evaluating ${OFFSITE} > 0.

What about BASH?

The required notation is nearly identical to TCSH:

_OFFSITE=$(cidrchk 10.0.0.0/20 66.55.32.0/20 >/dev/null)
export OFFSITE=$?

if (( ${OFFSITE} )); then
    #do something clever to prevent personal hardship
fi

Options

usage: cidrchk [-h] [--ignore IGNORE] [--debug] [--verbose] cidr [cidr ...]

Detects whether or not any ethernet devices match to a defined CIDR range.

positional arguments:
  cidr                  IP range(s) to detect

optional arguments:
  -h, --help            show this help message and exit
  --ignore IGNORE, -i IGNORE
                        IP range(s) to ignore (Default: link-local and
                        localhost)
  --debug, -d
  --verbose, -v

Bug Reporting

Submit bug reports via this project's issue tracker: https://github.com/jhunkeler/cidrchk/issues

Please remember to include your computer's operating system, the name of the shell you executed cidrchk from, the output of cidrchk -d, and any relevant code snippets you may have.