Port 500 — IPsec ISAKMP
Quick reference for TCP/UDP port 500, used by IPsec ISAKMP. Includes what the service does, security guidance and related ports.
What is port 500?
IPsec key exchange.
What port does IPsec ISAKMP use?
IPsec ISAKMP listens on port 500 by default.
Is port 500 open? How to check
Run one of these from your computer, replacing HOST with the IP address or domain you want to test.
nc -zvu HOST 500
Test-NetConnection HOST -Port 500
nmap -sU -p 500 HOST
A refused or timed-out connection means the port is closed or filtered by a firewall.
Security guidance
Medium risk — open with care
Port 500 (IPsec ISAKMP) can safely face the internet if you keep the software up to date, restrict admin endpoints, and use TLS where possible. Audit who can reach it and watch your logs.
Related ports
Frequently asked
What is port 500 used for?+
Port 500 is the standard TCP/UDP port for IPsec ISAKMP. IPsec key exchange.
What port does IPsec ISAKMP use?+
IPsec ISAKMP listens on port 500 by default.
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