I just observed some repeated logs with dmesg on two of my OpenWRT devices running the latest 24.10.0. One is an Edgerouter-X, the other one an X86-based router (APU2C4), so different CPU arch and network drivers. The repeated logs look like:
[ 255.296109] igb 0000:03:00.0 eth2: left allmulticast mode
[ 255.413475] igb 0000:03:00.0 eth2: entered allmulticast mode
[ 260.910925] igb 0000:03:00.0 eth2: left allmulticast mode
[ 261.033485] igb 0000:03:00.0 eth2: entered allmulticast mode
[ 261.073369] igb 0000:02:00.0 eth1: entered allmulticast mode
[ 265.787921] igb 0000:03:00.0 eth2: left allmulticast mode
[ 265.903506] igb 0000:03:00.0 eth2: entered allmulticast mode
[ 265.909623] igb 0000:02:00.0 eth1: left allmulticast mode
[ 266.073469] igb 0000:02:00.0 eth1: entered allmulticast mode
[ 561.576850] igb 0000:03:00.0 eth2: left allmulticast mode
[ 561.718932] igb 0000:03:00.0 eth2: entered allmulticast mode
[ 561.724991] igb 0000:02:00.0 eth1: left allmulticast mode
[ 561.818923] igb 0000:02:00.0 eth1: entered allmulticast mode
Same logs on Edgerouter-X with a different network driver.
Every 5 mins or so, all network interfaces seem to repeat the same left/entered allmulticast mode for no obvious reason. Network traffic does not seem impacted. Should I be worried? What could be causing those up/downs? Any advice appreciated, thanks!
Same to me
[ 36.203235] br-lan: entered allmulticast mode
[ 36.249380] br-lan: left allmulticast mode
[ 36.367259] br-lan: entered allmulticast mode
[ 40.962047] br-lan: left allmulticast mode
[ 41.111655] br-lan: entered allmulticast mode
[ 3510.556749] br-lan: left allmulticast mode
[ 3510.701014] br-lan: entered allmulticast mode
[ 3611.578967] br-lan: left allmulticast mode
[ 3611.745631] br-lan: entered allmulticast mode
[42924.393607] br-lan: left allmulticast mode
[42927.151144] br-lan: entered allmulticast mode
[45136.328481] br-lan: left allmulticast mode
[45136.607559] br-lan: entered allmulticast mode
[45145.789253] br-lan: left allmulticast mode
[45788.614113] br-lan: entered allmulticast mode
[46570.695057] br-lan: left allmulticast mode
[46570.962996] br-lan: entered allmulticast mode
[46578.993948] br-lan: left allmulticast mode
[47549.909984] br-lan: entered allmulticast mode
[47988.934290] br-lan: left allmulticast mode
[47989.184200] br-lan: entered allmulticast mode
[69249.520609] br-lan: left allmulticast mode
[69252.122961] br-lan: entered allmulticast mode
[73591.762876] br-lan: left allmulticast mode
[73594.341932] br-lan: entered allmulticast mode
[73893.031034] br-lan: left allmulticast mode
[73893.331107] br-lan: entered allmulticast mode
[74925.932119] br-lan: left allmulticast mode
[74928.548648] br-lan: entered allmulticast mode
[75070.718983] br-lan: left allmulticast mode
[75070.982822] br-lan: entered allmulticast mode
[76229.397129] br-lan: left allmulticast mode
[76229.666824] br-lan: entered allmulticast mode
[76717.499711] br-lan: left allmulticast mode
[76717.793889] br-lan: entered allmulticast mode
[140012.819307] br-lan: left allmulticast mode
[140012.922146] br-lan: entered allmulticast mode
[141226.700293] br-lan: left allmulticast mode
[141226.813893] br-lan: entered allmulticast mode
At last I am not the only one 
Since I get the same behaviour no matter what router I use, I am starting to suspect something from my ISP (SFR). Do you have the same ISP by any chance?
The issue creeped up with 24.10 version. It doesn't appear so often in 24.10.1, don't know about 24.10.2 as I didn't try it yet.
nitroshift