UDP port 500 is the ISAKMP protocol, part of IPSEC. You can define this as a 'port' service for NMIS to check; see Managing Servers and Services with NMIS8 for details.
Please be aware that remotely checking UDP ports for openness is not entirely reliable as UDP is a connection-less protocol.
Hello,
How can I monitor VPN port 500.
No icmp is available.
Regards,
Johny