Media diagnostics · Primary-source explanation; examples are illustrative. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Keep the transport assumption current
RFC 7766 specifies DNS TCP support requirements and discusses the growth of response sizes, including IPv6 and DNSSEC related data. Although many DNS transactions use UDP, TCP is not reserved exclusively for full zone transfers. A network policy based on that old assumption can produce a narrower failure than all DNS is broken. Preserve the actual query, response and transport when a large answer behaves differently from a small one.
Compare equivalent requests
For an original administrator led diagnostic plan, use a harmless hostname and the same requested record type when comparing transport behaviour. Record whether the initial response was incomplete or whether another request followed. A small unrelated lookup succeeding over UDP is useful but answers a different question. Do not change a managed firewall or public resolver configuration without understanding the intended policy and the applicable service documentation.
Separate support evidence from a fix
A report can state that ordinary name resolution works in one tested case while a documented TCP dependent case fails. That is more useful than replacing it with a blanket internet outage label. It also does not prove that a video player itself uses TCP DNS directly, since applications can use system resolvers or other supported arrangements. This article explains why transport coverage matters and does not certify any router, DNS provider or UK IPTV delivery path from one lookup.