An entry comes in three kinds: an exact domain, a subdomain pattern and an address range in CIDR notation. The difference is the same as in any network policy: a pattern covers the whole subtree of names, including hosts you have never heard of and ones that may appear tomorrow, while an exact domain covers only itself. When composing your own list it is worth preferring exact entries and adding a pattern only where subdomains are actually used - for example with artifact storage that has dynamic host names.

The sign of a network restriction in real work rarely looks like a network error. More often a package manager fails during dependency resolution, an image download hangs or a tool's cache silently stays empty, and the output shows only the top-level failure. So the first step is to find the specific host that could not be reached, and only then to decide. That host is the missing entry; everything else in the output is usually a consequence.

The main limitation to remember: an address list governs where it is possible to reach but not what comes back. An allowed registry can serve a package containing anything, and an allowed source host a repository with hostile content. A network policy reduces the surface but does not check meaning, and it works as one layer among several rather than as a replacement for the rest.

The gap is closed by other mechanisms, and it is worth naming them alongside. A version lockfile and checksums answer for the content being exactly what was expected rather than a substitution under the same name. An internal registry mirror narrows the source to a single address you control and, as a bonus, makes the build reproducible when the outside world is unavailable. In sensitive environments a short list plus a mirror of your own is almost always better than a long list of someone else's addresses.

There is also a practical technique: start from the default set, observe actual refusals and add what is missing precisely. That way you get a list that reflects your real build rather than someone's idea of it. And, more importantly, every added entry is explainable: it appeared in response to a specific need rather than just in case, and it can be removed when the need is gone.

The engineering conclusion is simple: the default list is a convenient base for development rather than a security policy. For sensitive environments a list of your own is assembled; for ordinary work the base is used and extended. In both cases remember that an open domain is permission to reach rather than a guarantee about the content.

The typical failures are predictable. Treating the default list as a security policy. Turning on the mode without domain restrictions to avoid dealing with it. Writing patterns where exact entries would do. Reading the topmost build error instead of finding the host that was refused. And adding addresses in advance instead of reacting to a specific refusal.