Current behaviour

Tests should not try to open connections to the internet because:

• they may succeed or fail unpredictably, depending on external environment
• are slow
• dox the developer to their ISP that they are running Bitcoin Core tests

Expected behaviour

Tests should only open local connections (e.g. on the lo interface).

Enforce this in the CI, having it to detect non-local traffic and fail accordingly.

Steps to reproduce

Run the functional tests and monitor the traffic.

Relevant log output

No response

How did you obtain Bitcoin Core

Compiled from source

What version of Bitcoin Core are you using?

master@22ef95dbe3e467039e6cd18988e66557d94041d1

Operating system and version

Ubuntu 28.04 LTS

This is being fixed in two parts:

• Fix all tests as of Jan 15 2025: test: avoid internet traffic #31646
• Detect future regressions in CI: ci: detect outbound internet traffic generated while running tests #31349