I just discovered this, and I thought it was worth documenting here in the forums.
It appears that the 5N has complete support for IPv6. I just configured my router to enable IPv6, and what a surprise to see this (info anonymized, of course):
# ifconfig -a
eth0 Link encap:Ethernet HWaddr XX:XX:XX:XX:XX:XX
inet addr:192.168.xxx.xxx Bcast:192.168.xxx.xxx Mask:255.255.255.0
inet6 addr: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/64 Scope:Global
inet6 addr: xxxx::xxxx:xxxx:xxxx:xxxx/64 Scope:Global
inet6 addr: xxxx::xxxx:xxxx:xxxx:xxxx/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:656502837 errors:0 dropped:0 overruns:0 frame:0
TX packets:103041726 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:532
RX bytes:1185076091 (1.1 GiB) TX bytes:1455609279 (1.3 GiB)
Interrupt:8
Sadly, the FS does not support IPv6.