Port 81 — HTTP alt
Quick reference for TCP/UDP port 81, used by HTTP alt. Includes what the service does, security guidance and related ports.
What is port 81?
Alternate HTTP port; used by many router admin panels and Synology DSM.
What port does HTTP alt use?
HTTP alt listens on port 81 by default.
Security guidance
Medium risk — open with care
Port 81 (HTTP alt) can safely face the internet if you keep the software up to date, restrict admin endpoints, and use TLS where possible. Audit who can reach it and watch your logs.
Related ports
Frequently asked
What is port 81 used for?+
Port 81 is the standard TCP/UDP port for HTTP alt. Alternate HTTP port; used by many router admin panels and Synology DSM.
What port does HTTP alt use?+
HTTP alt listens on port 81 by default.
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