How to automatically configure IPv6

[Aaron LI]

Hi DFlyers,


I'm studying in an university, where IPv6 is provided.  But all IPv6
addresses are directly and automatically distributed from the shcool's
routers, i.e., each of my machine will get a /128 address via DHCP.(*)

Yesterday, I configured "IPv6 pass-through" for my router (flashed with
DD-WRT), and my Linux boxes inside the LAN can automatically obtain IPv6
configurations, e.g.,

debian-linux> /sbin/ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.234  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 2001:da8:8000:6440::1188  prefixlen 128  scopeid 0x0<global>
        inet6 fe80::49a6:fb37:128a:a30b  prefixlen 64  scopeid 0x20<link>
        ether fc:aa:14:dc:35:1a  txqueuelen 1000  (Ethernet)

However, I cannot make my DFly box with IPv6 automatically configured. 
Here is my related settings in "/etc/rc.conf"(**):

ifconfig_em0="inet 192.168.1.237 netmask 255.255.255.0"
defaultrouter="192.168.1.1"
ipv6_enable="YES"
ipv6_network_interfaces="em0"
ipv6_ifconfig_em0="DHCP"

dfly> uname -a
DragonFly dflyvbox.aaronly.me 4.9-DEVELOPMENT DragonFly 2032f72fa-
DEVELOPMENT #1: Sun Jun 11 22:10:06 CST 2017

dfly> ifconfig em0
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=1b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING>
	inet 192.168.1.237 netmask 0xffffff00 broadcast 192.168.1.255
	inet6 fe80::a00:27ff:fe91:4474%em0 prefixlen 64 scopeid 0x1 
	ether 08:00:27:91:44:74
	media: Ethernet autoselect <rxpause> (1000baseT <full-duplex>)

How could I make DFly to automatically configure IPv6?  Thanks a lot.


(*) Some time ago, I tried to configure my DD-WRT router with IPv6
prefix delegation in order to enable IPv6 for my LAN, but in no vein. 
Now I found that this configuration was not supported by the school.

(**) I also tried without 'ipv6_ifconfig_em0="DHCP"', but the results
were the same.


Cheers,
-- 
Aly
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