What is this

I guess the "500" represents the number of the error.

500 is the default port IPsec traffic is on.
I guess someone is trying to put a IPsec tunnel online.

What is the solution to help me

Switch off ipsec and block unwanted communication by firewall.

What is the solution to help me

First, tell us what the problem is.

Is the remote IP one of your VPN clients attempting to connect to the VPN server?

• If so, they are failing to connect for some reason.
  1. Enable IPSec debugging.
  2. Find out what the error was.

If the remote IP is not one of your users attempting to make a VPN connection, you have two choices.

1. Ignore the log entries when crackers fail to log in to your VPN server.
2. Use firewall rules to block access to your VPN server from locations from which it is not likely for your users to connect.

Port 500 is used for IPSec IKE (phase1) connection setup.

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