ike-scan discovers IKE hosts and can also fingerprint them using the
retransmission backoff pattern.

ike-scan does two things:

a) Discovery: Determine which hosts are running IKE.
   This is done by displaying those hosts which respond to the IKE requests
   sent by ike-scan.

b) Fingerprinting: Determine which IKE implementation the hosts are using.
   This is done by recording the times of the IKE response packets from the
   target hosts and comparing the observed retransmission backoff pattern
   against known patterns.

The retransmission backoff fingerprinting concept is discussed in more
detail in the UDP backoff fingerprinting paper which should be included
in the ike-scan kit as udp-backoff-fingerprinting-paper.txt.

The program sends IKE main mode requests to the specified hosts and displays
any responses that are received.  It handles retry and retransmission with
backoff to cope with packet loss.  It also limits the amount of bandwidth
used by the outbound IKE packets.