How to do it...

To configure ike-scan follow the given steps:

Browse to the directory where ike-scan is installed.
Install autoconf by running the following command:

        apt-get install autoconf

Run autoreconf --install to generate a .configure file.
Run ./configure.
Run make to build the project.
Run make check to verify the building stage.
Run make install to install ike-scan.
To scan a host for an aggressive mode handshake, use the following commands:

        ike-scan x.x.x.x -M -A

The following screenshot shows the output for the preceding command:

Sometimes we will see the response after providing a valid group name like (vpn):

        ike-scan x.x.x.x -M -A id=vpn

The following screenshot shows the example of the preceding command:

We can even brute force the groupnames using the following script:
https://github.com/SpiderLabs/groupenum.

The command:
./dt_group_enum.sh x.x.x.x groupnames.dic