Description

Attempting to test multicast sockets results in routing errors, which suggests that the code is running without "local network access" permissions.

Ideally this would be configurable, so that code could be tested to ensure that it doesn't need this permission, but when it is necessary for a certain function it would be nice to have.

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 20.04
• Ubuntu 22.04
• Ubuntu 24.04
• macOS 12
• macOS 13
• macOS 13 Arm64
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• Windows Server 2019
• Windows Server 2022

Image version and build link

https://github.com/twisted/twisted/actions/runs/11713225981/job/32625578908?pr=12357

Is it regression?

sort of? it regressed from macos 14

Expected behavior

I would expect to be able to test multicast sockets

Actual behavior

Multicast sockets give a "no route to host" error when sending

Repro steps

1. bind a multicast socket
2. send some data to it