Time synchronization ports
Overview
NTP is simple but abused for reflection attacks. Restrict mode 6/7 queries, use authenticated time where possible, and keep servers patched.
Ports in this category10
Range coveredAll registry ranges
All Time synchronization port numbers
Every port below is assigned to this category in the registry or by a widely used convention. Open a port for its check and block commands, risk rating and troubleshooting notes.
| Port | Service | Transport | Risk | Description |
|---|---|---|---|---|
| 52 | XNS-TIME | TCP / UDP | Standard/Low | XNS Time Protocol |
| 119 | NNTP | TCP / UDP | Standard/Low | Network News Transfer Protocol |
| 123 | NTP | TCP / UDP | Medium | Network Time Protocol |
| 433 | NNSP | TCP / UDP | Standard/Low | NNTP for transit servers (NNSP) |
| 563 | NNTPS | TCP / UDP | Standard/Low | nntp protocol over TLS/SSL (was snntp) |
| 580 | SNTP-HEARTBEAT | TCP / UDP | Standard/Low | SNTP HEARTBEAT |
| 4881 | SOCP-T | UDP | Standard/Low | SOCP Time Synchronization Protocol |
| 5319 | ROUGHTIME | TCP / UDP | Standard/Low | Roughtime time synchronization |
| 8384 | MARATHONTP | UDP | Standard/Low | Marathon Transport Protocol |
| 23053 | GNTP | TCP | Standard/Low | Generic Notification Transport Protocol |
Other categories
Authentication and access 19Caching and in-memory stores 10Containers and orchestration 10DNS and naming 10Databases 54Development servers 13Directory services 14Email 26File transfer and sharing 27Gaming 6Infrastructure and administration 30IoT and device telemetry 7Message queues and streaming 17Monitoring and metrics 29Networking and proxies 31Printing 19RPC and service APIs 14Remote access 29VPN and tunnelling 10Voice and real-time media 29Web and HTTP 62Windows networking 14
Primary data: IANA Service Name and Transport Protocol Port Number Registry, plus clearly marked community conventions.
Last reviewed 2026-10-30 · Methodology · About · Privacy