We know that IPSec is a suite of protocols used to establish is a secure VPN connection between two remote networks with the help of VPN gateways (routers or firewalls). Before the IPSec tunnel can be established to secure to traffic, a negotiation process needs to take place between the two peers (routers or firewalls) to agree on mutual parameters for the IPSec tunnel. The protocol that handles the exchange of the mutual parameters/policies is known as Internet Security Association and Key Management Protocol (ISAKMP).
The policies that are exchanged between the peers are used to determine the methods of authentication, such as a pre-shared key or the use of RSA signatures, the encryption algorithm for data confidentiality between the peers and the remote networks, the key exchange group (whether it's Diffie-Hellman 1, 2, or 5), and the hashing algorithm for validating...