Port4500— IPSec NAT-Traversal
UDP 4500 carries IPSec/IKEv2 NAT-Traversal (NAT-T). When a VPN client sits behind NAT, IKE negotiates a switch from port 500 to 4500 and encapsulates ESP traffic there. It almost always pairs with UDP 500.
Registry assignments, software defaults and local listeners are different things. A port number alone does not identify or secure a service.
Configuration and troubleshooting
For IPSec VPN failures behind NAT: allow both 500 and 4500, and either permit ESP (IP protocol 50) or confirm NAT-T encapsulation is active. `ipsec statusall` (strongSwan) shows IKE_SA state; Windows clients log to Event Viewer. Cloud VPN gateway docs list 500/4500 as hard dependencies.
Important limitations
Some carrier and corporate firewalls block 4500, making the VPN work on some networks only. Diagnose by switching networks first (mobile hotspot). Port 4500 carries IPSec only — never repurpose it.
Read-only checks: run on the server host
Choose the commands for your OS. Check TCP and UDP separately. No result is not a lasting availability guarantee; inspect host and container separately.
Linux
sudo ss -lunp 'sport = :4500'macOS
sudo lsof -nP -iUDP:4500Windows PowerShell
Get-NetUDPEndpoint -LocalPort 4500Sources and review
Sources checked on:
This review covers the explanations and sources on this page, not your device or every community software entry below.
Software Using This Port (1 software)
Community software entries: links are references, not individual verification.
Usage Suggestions
- Before using port 4500, please confirm it is not occupied by other services
- If you encounter port conflicts, consider using other ports or stopping the occupying service
Frequently asked questions
What is port 4500 used for?
Port 4500 sits in the Security & Authentication category. This page lists the registered purpose and the software commonly associated with it; to see what is actually listening on a specific machine, check the process with ss/netstat.
Is port 4500 TCP or UDP?
The registered protocol on this page is UDP. The same number behaves independently on each protocol: TCP may be listening while UDP is idle, so check them separately.
How do I check if port 4500 is in use?
On Linux: sudo ss -tlnp 'sport = :4500' for an exact port match. On macOS: sudo lsof -nP -iTCP:4500 -sTCP:LISTEN. On Windows PowerShell: Get-NetTCPConnection -LocalPort 4500 -State Listen. A listener counts as confirmed only when you can see the bind address and process name; without root/admin you will not see other users' processes.
Is port 4500 secure? Should I open it in my firewall?
A port number has no inherent security — it depends on whether the listening service is correctly configured and whether it needs exposure at all. Keep loopback/internal-only services firewalled; where public access is required, pair it with source restrictions, VPN or authentication. The caution section on this page lists port-specific risks.
Quick Info
- Port
- 4500
- Protocol
- UDP
- Categories
- Security & Authentication
- Usage Status
- 1 software in use
Related Ports
Need Help?
If you find incorrect information or need to add more, please submit correction information.
Submit Correction