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?