@DKHK That's right. IGMP, I am not sure. Leave the to be the default. I don't try or use Router--SW---PC. I am doing researches on this and trying to help you out. That'll also be some experience for...

@SlowUsbPort The link I posted in the last reply was some kind of workaround.

@SlowUsbPort https://community.tp-link.com/en/business/forum/topic/511086 I am repeating what the User Guide says. And I am not dev. You wanna do that and you can refer to the workaround. Not "I...

@andrewclark7486 Wrong forum? It's business forum for TPLINK. What kind of device you have?

@SlowUsbPort Premise of the Link backup is Load Balance. But, read the User Guide. Sessions are not forwarded to the WAN2 if Primary is online, which means the Load Balance is not working because of...

@DKHK Try this guide first: https://www.tp-link.com/us/support/faq/2156/ Switch should pass through this packet. Did you try the default settings on your switch? Set up the static ARP on your switch