Public bug reported:

This is occurring on Ubuntu 20.04 with kernel 5.4.0-56-generic.

To demonstrate, run
$ sudo tcpdump -nv -ienp4s0 igmp
(adjusting the interface name appropriately).

The result will be 0 packets captured, even though all other Ubuntu systems on 
the same ethernet
lan are reporting igmp queries from the router and responding with reports 
every minute or so.

One consequence of this is that a CUPS server using the Comet Lake onboard 
ethernet controller
cannot be detected by any clients, except within the first 120 seconds after 
restarting the
avahi-daemon. Since the Comet Lake server does not receive the igmp queries, it 
does not respond
with a report and so the router unsubscribes the interface from the multicast 
group that is used
by avahi and bonjour.  This makes the CUPS server disappear.

The output of ubuntu-bug linux is attached.

** Affects: ubuntu
     Importance: Undecided
         Status: New

** Attachment added: "igc.txt"
   https://bugs.launchpad.net/bugs/1906418/+attachment/5440046/+files/igc.txt

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https://bugs.launchpad.net/bugs/1906418

Title:
  igc driver for Comet Lake  onboard 15f3 NIC drops all igmp packets

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