[MULTICAST FORWARDING] Multicast forwarding lacks receiver-aware decision making

[ankohuu]

Current multicast forwarding in NuttX is local-membership driven rather than receiver-aware

• IPv4, forwarding is based on the device’s IGMP group list, performing a fan-out/relay for groups joined locally. here
• IPv6, multicast packets are just forwarded. here

This issue discusses whether NuttX should evolve toward receiver-aware multicast forwarding

Such a change may involve:

• Control path: introducing IGMP/MLD snooping or similar mechanisms to learn downstream membership
• Data path: adding a multicast forwarding struct and corresponding forwarding logic
• User space: other potential support

From project history I found that NuttX has evolved to supporting multiple netdevs and basic forwarding, extending multicast forwarding may be a reasonable next step.

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

Ubuntu 24

NuttX Version

All version

Issue Architecture

[Arch: all]

Issue Area

[Area: Networking]

Host information

No response

Verification

• I have verified before submitting the report.

[ankohuu]

@acassis Seems there hasn’t been enough time for a thorough discussion on multicast forwarding. So I created this issue to track the topic and discuss further.

Thank you

[acassis]

Hi @ankohuu thank you very much for your detailed Issue. I agree this will be a good improvement. And it will make NuttX more compatible with high-end OSes. Do you think this new feature will require more memory (flash and RAM)? If so, does it make sense to have a config option to keep the old behavior for low end MCUs?