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8.8.8.8:53
1.1.1.1:123
192.168.0.1:161
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$ checkhost monitor --type udp port --interval 30s
Need continuous udp port monitoring?
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About
UDP Port Checker — Test UDP Connectivity Globally
UDP (User Datagram Protocol) is a connectionless transport protocol used for speed-sensitive applications where some packet loss is acceptable. Unlike TCP which establishes a formal connection, UDP sends packets without handshaking, making it faster but less reliable. UDP is used by DNS (port 53), VoIP and video conferencing (various ports), online gaming (game-specific ports), VPN protocols (OpenVPN on 1194, WireGuard on 51820, IKEv2 on 500/4500), streaming media, NTP time sync (port 123), and SNMP monitoring (port 161). Testing UDP ports is inherently trickier than TCP because there's no connection handshake to definitively confirm the port is open. An open UDP port may simply not respond, making it hard to distinguish from a filtered port. CheckHost tests UDP connectivity from multiple global locations, sending UDP probes and analyzing the response (or lack thereof) to determine port status.
Usage
How to Check UDP Ports With CheckHost
Enter the host and UDP port in the format host:port (e.g., 8.8.8.8:53 for DNS, my-vpn.com:51820 for WireGuard).
Select 'UDP' from the tool tabs and click Check to test from global locations.
Results show whether the UDP port appears open or filtered from each testing location.
Note: UDP testing is less definitive than TCP. An 'open' result means the port didn't respond with ICMP unreachable (which could mean a service is listening or a firewall is silently dropping). A 'closed' result (ICMP port unreachable received) is more definitive.
FAQ
Frequently Asked Questions
What are common UDP ports?
53 = DNS, 67/68 = DHCP, 69 = TFTP, 123 = NTP (time synchronization), 161/162 = SNMP (monitoring), 500 = IKE/IPSec VPN, 514 = Syslog, 1194 = OpenVPN, 4500 = IPSec NAT-T, 5060 = SIP (VoIP), 51820 = WireGuard VPN, 27015+ = Game servers (Steam, etc.).
Why is UDP testing less reliable than TCP?
TCP has a 3-way handshake (SYN → SYN-ACK → ACK) that definitively confirms a port is open. UDP has no handshake — an open port may not respond at all, making it look identical to a filtered port. Only a 'closed' UDP port is definitive: the OS sends back an ICMP 'Port Unreachable' message. For the most reliable UDP test, use application-specific probes (e.g., a DNS query for port 53).
What's the difference between TCP and UDP?
TCP = reliable, ordered delivery with error checking and retransmission. Best for: web browsing, email, file transfers, APIs. UDP = fast, no guaranteed delivery, no connection overhead. Best for: gaming, video streaming, VoIP, DNS queries, VPN tunnels. TCP guarantees your data arrives intact; UDP prioritizes speed over reliability.