Hostname Matrix

What to test here

This website is available under multiple hostnames that deliberately advertise and accept different protocol combinations. The hostnames are designed to make HTTP version selection visible: DNS HTTPS records, Alt-Svc headers, TLS ALPN negotiation, server-side protocol enforcement, and port hints can be tested separately.

If you want to learn more about how those mechanisms drive protocol selection, read DNS HTTPS Records and Alt-Svc. Click any hostname below to load the page on that host; the protocol widget in the header updates to show what was actually negotiated.

Click any hostname below to load this page on that host. The protocol widget in the header shows what was actually negotiated. To compare all hostnames in one view, open the Protocol Detection page.

Legend

Each protocol is indicated by its color badge as shown here. H3 stands for HTTP/3 over QUIC and TLS, H1C stands for HTTP/1.1 in cleartext (HTTP — not TLS encrypted). Different browsers show different protocol selection behavior. We show the expected behavior for the most widely used browsers and indicate each with a small logo.

Reference Hostnames — all ports

The reference hostnames accept all protocols on the relevant ports. Together with h2-h3-alt in the next section, they form a three-way test for HTTP/3 discovery:

• sse-testcenter.org advertises HTTP/3 through both DNS HTTPS records and Alt-Svc.
• www.sse-testcenter.org advertises HTTP/3 through DNS HTTPS records only.
• h2-h3-alt.sse-testcenter.org advertises HTTP/3 through Alt-Svc only.

This separates DNS-based discovery from learned Alt-Svc discovery. Safari is expected to use only the DNS HTTPS signal. Chrome is expected to use both mechanisms independently.

curl --http3 https://sse-testcenter.org/

curl --http2 https://www.sse-testcenter.org/

TLS Hostnames — port 443

Each hostname enforces only the protocols its name lists — the server rejects ALPN tokens it does not advertise. The DNS HTTPS record priority (p1 preferred) lets you verify whether an SSE gateway respects the advertised ALPN order. h2-h3-alt has no DNS HTTPS record, but supports H2 and H3 and sends an Alt-Svc header advertising H3. With a fresh Safari website state, Safari is expected to start and remain on H2. We have not observed Safari switching to H3 based on Alt-Svc alone. However, after Safari has learned H3 support for another related hostname under `sse-testcenter.org`, it may also attempt H3 for this hostname. Chrome upgrades via Alt-Svc on the next page object (usually within the same page load). h3 (H3-only) is the most demanding: Chrome has no Alt-Svc and cannot fall back to H2, so it will fail unless it follows the DNS HTTPS record.

curl --http3 https://h1-h3.sse-testcenter.org/

curl --http3 https://h2-h3.sse-testcenter.org/

curl --http3 https://h2-h3-alt.sse-testcenter.org/

curl --http2 https://h1-h2.sse-testcenter.org/

curl --http2 https://h2.sse-testcenter.org/

curl --http1.1 https://h1.sse-testcenter.org/

curl --http3 https://h3.sse-testcenter.org/

TLS Hostnames — port 8443

The DNS HTTPS records for these hostnames advertise port 8443, not the default port 443. This creates two distinct test scenarios: clicking a link without an explicit port tests whether the client follows the DNS HTTPS port hint; clicking with :8443 forces the port directly.

Explicit port — :8443 in URL

The URL includes :8443 explicitly, so all clients connect to the right port regardless of DNS HTTPS support. This is the baseline for comparing protocol negotiation at port 8443 without the port-hint variable.

curl --http2 https://h2-8443.sse-testcenter.org:8443/

curl --http3 https://h3-8443.sse-testcenter.org:8443/

curl --http3 https://h2-h3-8443.sse-testcenter.org:8443/

DNS-guided — no port in URL

The hostnames in this subsection are intentionally not linked. A plain https://hostname/ URL depends on the client following the DNS HTTPS port hint. Clients that ignore the port hint will try standard port 443 and will fail.
For testing, copy/paste the URL to your address bar.

Cleartext Hostnames — port 80

No TLS. Most modern browsers will show a "Not Secure" indicator. SSE products typically inspect cleartext HTTP even when they do not perform TLS inspection. Note that H2C requires the client to send the HTTP/2 connection preface without ALPN negotiation — many proxies do not support it.

curl --http1.1 http://h1c.sse-testcenter.org/

curl --http2-prior-knowledge http://h2c.sse-testcenter.org/

curl --http2-prior-knowledge http://h1c-h2c.sse-testcenter.org/

Cleartext Hostnames — port 8080

Same as the port 80 group but on port 8080. Useful for testing forward proxy configurations that intercept a specific alternate port.

curl --http1.1 http://h1c-8080.sse-testcenter.org:8080/

curl --http2-prior-knowledge http://h2c-8080.sse-testcenter.org:8080/

Want to see all hostnames at a glance? The Protocol Detection page polls every hostname in parallel and shows the negotiated protocol for each — useful for a quick overview when you are not inspecting a specific host.