Alt-Svc

Advertises an alternative service for reaching an origin.

Use Alt-Svc to let clients discover HTTP/2 or HTTP/3 endpoints without changing the origin URL. The client must validate the alternative service.

httpheaderhttp2http3

Reference (http)

Alt-Svc: h3=":443"; ma=86400

Use Alt-Svc to let clients discover HTTP/2 or HTTP/3 endpoints without changing the origin URL. The client must validate the alternative service.

Common mistakes

Treating an Alt-Svc advertisement as a redirect or serving it with an invalid certificate.

IANA registry: http-fields/field-names

Sources