www hostname

This follows www.<domain> to the end of whatever chain it is published as, up to eight hops, and reports where it lands. A missing www is a warning when the apex resolves — a good share of visitors and a great many old links still carry it, and they get a DNS error rather than your site — and only information when neither form resolves, since that domain is not hosting a website at all.

Two of the failures are about chains rather than about www itself. A chain longer than eight hops, or one that loops, will not resolve for most resolvers, because every resolver gives up after some number of hops — ours gives up after eight, so this report is one of the ones that saw it first. A chain that terminates without an A or AAAA record is the more common failure, and it is the signature of a service switched off without the DNS being tidied afterwards.

That last state deserves more attention than a broken hostname usually gets, because it is also the shape of a subdomain takeover. A CNAME pointing at a hostname on a cloud or SaaS platform that has since been deprovisioned resolves to nothing today — and to whatever the next person to claim that name on that platform puts there tomorrow, served under your domain and, if you use a wildcard certificate, under your certificate.

Publish www as a CNAME to your host, or as A and AAAA records alongside the apex. Then pick one of the two forms as canonical and redirect the other to it with a 301, so links, analytics and cookies do not split across two hostnames.

Make sure the certificate covers both names. Serving a redirect from the non-canonical name still requires a valid TLS handshake on that name first, and a certificate for only one of the two produces a browser warning on the way to the redirect.

Audit dangling CNAMEs across the whole zone, not just www. Any alias pointing at a platform hostname you no longer own is a takeover waiting for somebody to notice, and the fix is a one-line deletion — the cheapest security work available.