Is port 81 (HTTP Alternate) dangerous?

Port 81 is classified as medium risk. It is commonly exposed but consider using encrypted alternatives where available and monitor activity.

Should port 81 be open on my firewall?

Port 81 can be open but should be monitored closely. Keep the service updated and prefer encrypted alternatives where available.

What transport protocol does port 81 use?

Port 81 (HTTP Alternate) uses the TCP transport protocol and falls under the Web category.

:81 (TCP)

HTTP Alternate

Medium Risk

TCP — 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.

Related Ports — Web

70 Gopher 80 HTTP 280 http-mgmt 414 InfoSeek 418 Hyper-G 443 HTTPS 454 ContentServer 593 HTTP-RPC-EPMAP

Related Terms

ARP FTP HTTP ICMP IMAP NTP