IPv6 BIRD filters

Hello Guys, Anyone create maybe a good filters for BIRD IPv6 upstreams? I just add this to my import filter: import filter { if bgp_path.len > 49 then reject; if (net.len < 16) || (net.len > 48) then reject; accept; }; But i saw i get strange routing: root@it-bgp:~# birdc6 show route 2404:1710::/28 BIRD 1.6.3 ready. 2404:1710::/28 via 2a02:XXXX:XXXX:1 on eth0 [Italy 13:52:47 from 2a02:XXXX:XXXX::2] * (100/?) [AS65332i] Anyone got any good filter to block something like this? Best Regards Marek