Jetty version(s)
Jetty 12.1.4

Jetty Environment
Jetty demo

HTTP version
HTTP/3

Java version/vendor (use: java -version)

openjdk version "25.0.1" 2025-10-21
OpenJDK Runtime Environment (Red_Hat-25.0.1.0.8-1) (build 25.0.1+8)
OpenJDK 64-Bit Server VM (Red_Hat-25.0.1.0.8-1) (build 25.0.1+8, mixed mode, sharing)

OS type/version
Fedora release 43 (Forty Three)

Description
I think Jetty demo has wrong default configuration for HTTP/3. After running demo on default settings my netstat output looks like:

  mn:~$ netstat -anp | grep 38203
  tcp6  0  0 :::8443   :::*       LISTEN      38203/java
  tcp6  0  0 :::8080   :::*       LISTEN      38203/java
  udp6  0  0 :::8444   :::*                   38203/java

In browser debug (F12) I see header:
alt-svc: h3=":8443"

HTTP/3 specification for this header:
https://datatracker.ietf.org/doc/html/rfc9114#name-http-alternative-services
says about UDP port, so I think it should be header alt-svc: h3=":8444", or default config should use 8443 as as a default UDP port.

How to reproduce?

1. run demo as described in documentation and add http3 module
2. look at netstat output and alt-svc response headers