IPv6 with DHCP -- how is default route set?

[Eloy Paris <peloy chapus net>]

Hello,

The company I work for has an IPv6-enabled network that requires
configuration via DHCP. I get assigned a global IPv6 address just fine
after configuring the NetworkManager entry for my NIC with "Automatic,
DHCP only".

The problem, however, is that a default route is never installed. I am
confused as to who is responsible for setting up the default route,
which should be learned via Neighbor Discovery router advertisement
messages, which I am seeing:

11:22:13.534922 IP6 (class 0xe0, hlim 255, next-header ICMPv6 (58) payload length: 64) 
fe80::208:e3ff:feff:fd90 > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 64
        hop limit 64, Flags [managed], pref medium, router lifetime 1800s, reachable time 0s, retrans time 0s
          source link-address option (1), length 8 (1): 00:08:e3:ff:fd:90
            0x0000:  0008 e3ff fd90
          mtu option (5), length 8 (1):  1500
            0x0000:  0000 0000 05dc
          prefix info option (3), length 32 (4): 2001:x:x:x::/64, Flags [onlink], valid time 0s, pref. time 0s

For this to work, do I need a userspace daemon that processes these
router advertisement messages? Or can the kernel install the default
route if some tunables like accept_ra are set properly? I notice that
NetworkManager seems to set accept_ra to 0, though, and there is no way
to configure the behavior that I can see.

I've searched online left and right but have not been able to find a
conclusive answer on how to properly set up NetworkManager so IPv6 with
DHCP configuration is usable beyond the local subnet. Pointers would be
greatly appreciated.

Running NetworkManager 1.0.4 with Linux kernel 4.2.0 (this is what comes
with Ubuntu 15.10, which is about to release in the next day or two).

Cheers,

Eloy Paris.-