Filtering IPv6 RA on relay mode

My router is running on RA relay mode, only by this way, downstream devices can get their IPv6 global unicast address.
But my ISP has misconfigured RA for over two weeks.

Unfortunately, each of my devices registered to three /64 subnets isn't good news for me. Only one of them is connected to the Internet!
What‘s worse, all my devices running Linux (including my Android phone and the router itself) always stick on one of the broken two, instead of the working one. They lost their IPv6 Internet connection but believed they still had it. Thus, any IPv6 to IPv4 fallback costs tons of time waiting for an IPv6 connection timeout. Only my Windows laptop can choose the working one automatically.

I wonder if there are some methods to screen out the working subnet, not to send RA with the broken two subnets, since I had no way to manually adjust the router table of my Android phone.

PS: the working subnet has a constant prefix, it never changes.

Only if you could filter on the content of the RA packet. Check if iptables can do that.
However your ISP should fix that, not to look around in forums for workarounds.

Yeah, they should fix that. But they thought since this problem never influences Windows, there should be no problem...

Well, finally, with my help, the problem had been located. There is someone else broadcasting their RA. After the ISP asked them to stop doing this, the problem was solved.

Someone else in your house or in the network of your ISP?

Latter. Here is a university, that's why I need to use RA relay.

Still, they should have a minimum network hardening to avoid such issues.

Yeah, they should. But they just think IPv6 is a "plus" and are never willing to pay much attention to it since most users do not need IPv6... Hope they can take this incident seriously.

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