Happy Eyeballs
Testing: SVCB/HTTPS AliasMode Test

This test verifies whether the browser correctly processes HTTPS AliasMode records (priority 0) and initiates a follow-up query for the alias target name (Section 4.2.1).

The test runs four subtests side by side. The first — Direct (control) — connects directly to the alias target host, which has full A, AAAA, and HTTPS records. A successful result here confirms the server infrastructure is reachable. The second — Via AliasMode HTTPS — connects to a domain that carries only an AliasMode HTTPS record (priority 0) pointing to the same target; no A or AAAA records exist on the alias name itself. The third — Via ServiceMode HTTPS — uses a ServiceMode record (priority 1) whose TargetName points to the same target instead of ".", again without A or AAAA records on the owner name.

If the browser correctly chases the target name, it resolves it and connects successfully, shown as Target Followed. If it ignores the record, the DNS lookup returns no addresses and the connection fails (ERR).

The fourth subtest — HTTPS port Override — queries a domain whose ServiceMode record carries a port=8444 parameter alongside regular A and AAAA records. The connection succeeds either way: a browser that applies the port parameter connects to port 8444 (Port Followed), while one that ignores it connects to the default port 443 (Port Ignored).