Separate the name from the connection

A failed request can begin before a connection is attempted. Name resolution supplies an address; routing and transport must then reach it. Keeping these steps separate makes an investigation easier to reproduce.

Record what was resolved

A name can have several IPv4 or IPv6 addresses. Record the returned values, the resolver and the time of the check. A cached answer can remain valid until its time to live expires, even after an authoritative record changes.

Compare the same endpoint

Two devices may receive different answers or prefer different address families. Compare the address actually used by each connection before drawing conclusions from a hostname alone. A successful lookup is evidence about DNS, not proof that the remote service is reachable.

Keep verification intact

When testing a particular address, preserve the intended TLS hostname and certificate verification. Changing the connection address and changing the expected service identity are separate operations. Record certificate errors independently from transport timeouts.

Change one variable

Use a small known request, repeat it from the same network interface and preserve timestamps. Then compare a second network or resolver deliberately. This produces a useful before-and-after record without confusing several changes.