Please check whether this helps, I know that I am late :)
Yes, this is from the Wikipedia article, Internet Security Association and Key Management Protocol, but I didn't see any references so far to Wiki/RFC here in discussion.
ISAKMP defines the procedures for authenticating a communicating peer,
creation and management of Security Associations, key generation
techniques and threat mitigation (e.g. denial of service and replay
attacks). As a framework, ISAKMP is typically utilized by IKE for key
exchange, although other methods have been implemented such as
Kerberized Internet Negotiation of Keys. A Preliminary SA is formed
using this protocol; later a fresh keying is done.
ISAKMP defines procedures and packet formats to establish, negotiate,
modify and delete Security Associations. SAs contain all the
information required for execution of various network security
services, such as the IP layer services (such as header authentication
and payload encapsulation), transport or application layer services or
self-protection of negotiation traffic. ISAKMP defines payloads for
exchanging key generation and authentication data. These formats
provide a consistent framework for transferring key and authentication
data which is independent of the key generation technique, encryption
algorithm and authentication mechanism.
ISAKMP is distinct from key exchange protocols in order to cleanly
separate the details of security association management (and key
management) from the details of key exchange. There may be many
different key exchange protocols, each with different security
properties. However, a common framework is required for agreeing to
the format of SA attributes and for negotiating, modifying and
deleting SAs. ISAKMP serves as this common framework.
ISAKMP can be implemented over any transport protocol. All
implementations must include send and receive capability for ISAKMP
using UDP on port 500.