81
HTTP Alternate
Medium RiskTCP — Web
Port Overview
Port Number
81
Service Name
HTTP Alternate
Transport Protocol
TCP
Category
Web
Security Risk
Medium
Port Range
Well-Known (0-1023)
What is Port 81?
Port 81 is an unofficial alternate HTTP port used when port 80 is unavailable or blocked, commonly seen on home routers, development servers, and some commercial web appliances. Publicly exposed port 81 web services are frequently targeted by automated vulnerability scanners.
TCP
Web
Commonly Used
Security Considerations
Port 81 (HTTP Alternate) is classified as medium risk. While this service is commonly exposed, consider using encrypted alternatives where available.
Recommendation: Keep the service updated. Monitor logs for unusual activity.