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This document describes the issue faced by an user.


What is ISAKMP?

ISAKMP is a protocol which defines standar procedures and packet formats in order to establish, negotiate, modify and delete Security Associations. SAs contains the required information required to execute various network security services, some mentioned below:

  • IP layer services (header authentication and payload encapsulation)
  • transport or application layer services or self-protection of negotiation traffic.

ISAKMP also defines payloads which in turn is used for exchanging key generation and authentication data.


isakmp header.png


WIth the help of these formats user can achieve:

  • A consistent framework for transferring key and authentication data (independent of the key generation technique) encryption algorithm and authentication mechanism.

ISAKMP can easily be implemented over any transport protocol.All implementations must include send and receive capability for ISAKMP using UDP on port 500.


Core issue


When two peers use Internet Key Exchange (IKE) to establish IPSec associations, each peer sends its ISAKMP identity to the remote peer. It sends either its IP address or host name, depending on how it has its ISAKMP identity set.

The default ISAKMP identity on the PIX Firewall is hostname, so the PIX sends its Fully Qualified Domain Name (FQDN), instead of its IP address. If the other device does not understand that parameter, then a tunnel is not established.




Issue the isakmp identity address command to the PIX configuration to bring up VPN tunnels with non-Cisco devices. 

Refer to the isakmp command for configuration details.

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