[FS#580] Netgear R7800 does not receive multicast messages on LAN interfaces

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Graham Cobb (gcobb) 

Attached to Project - LEDE Project
Summary - Netgear R7800 does not receive multicast messages on LAN interfaces
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Netgear R7800 running lede-17.01.

Multicast packets are not received on LAN (wired) interfaces but work fine on WiFi interfaces. I think the problem is at device/driver level.

The problem was first noticed using Avahi, which did not see announcements on LAN interfaces. However it can be easily reproduced with a simple IP Multicast sender/receiver like https://github.com/GrahamCobb/Multicast-Client-Server-Example

To reproduce:

Run the "client" on the R7800 using:

client 232.0.1.1 4545 100


Run the "server" on another system using:

server 232.0.1.1 4545 100 1000


If the server is connected to the client using a WiFi interface, the messages are received. If it using a LAN, they are not.

The messages **are** received if the LAN interface is set in promiscuous mode (//ifconfig ... promisc//) or all multicast mode (//ifconfig ... allmulti//). They stop again immediately if the mode is turned off.

I believe this is the same problem as reported in https://forum.lede-project.org/t/ipv6-works-only-with-wan-in-promiscuous-mode/490/9 -- in that thread it is mentioned that the AC2600 (which uses the same driver) has the same problem.

As the problem goes away in promiscuous or all multicast modes, I am guessing that the device is just not sending the multicast packets to the driver. This could be a hardware bug, a bug in the multicast filter setup code in dwmac1000_core.c or the devicetree incorrectly reporting device characteristics such as the number of multicast filter bins.

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=580