What is the interface type on the upstream link? Are you sending v6 natively on the link, or is there some encapsulation? Static route, or some IGP, or BGP, or ? When you said "isn't answering", do you mean that you have an ndp cache entry, but when the unicast packet is sent, there is no link-level receiver? Or do you mean that there is no ndp entry, because it doesn't answer the ndp request packets? I'm reading code in -current, but look in src/sys/net/if_ethersubr.c:ether_output() and audit the memory handling. I haven't found anything yet, but that's what I would first suspect.
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