Android and DHCPv6 again

Wed Oct 7 01:09:09 UTC 2015

Your device may be getting an address, but without a recursive DNS server
it may be useless.

If you're going to do SLAAC you'll also need to supply your client with a
recursive DNS server. Android prefers RFC 6106. As you mentioned, Google
has decided not to support DHCPv6 in Android. Unfortunately some router
manufacturers are only now getting around to implementing RFC 6106.

BH

On Sat, Oct 3, 2015 at 9:52 PM, Baldur Norddahl <baldur.norddahl at gmail.com>
wrote:

> Hi
>
> I noticed that my Nexus 9 tablet did not have any IPv6 although everything
> else in my house is IPv6 enabled. Then I noticed that my Samsung S6 was
> also without IPv6. Hmm.
>
> A little work with tcpdump and I got this:
>
> 03:27:15.978826 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 120)
> fe80::222:7ff:fe49:ffad > ip6-allnodes: [icmp6 sum ok] ICMP6, router
> advertisement, length 120
> hop limit 0, Flags [*managed*, other stateful], pref medium, router
> lifetime 1800s, reachable time 0s, retrans time 0s
>  source link-address option (1), length 8 (1): 00:22:07:49:ff:ad
>  mtu option (5), length 8 (1):  1500
>  prefix info option (3), length 32 (4): 2a00:7660:5c6::/64, Flags [onlink,
> *auto*], valid time 7040s, pref. time 1800s
>  unknown option (24), length 16 (2):
>  0x0000:  3000 0000 1b80 2a00 7660 05c6 0000
>
> So my CPE is actually doing DHCPv6 and some nice people at Google decided
> that it will be better for me to be without IPv6 in that case :-(.
>
> But it also has the auto flag, so Android should be able to do SLAAC yes?
>
> My Macbook Pro currently has the following set of addresses:
>
> en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> ether 3c:15:c2:ba:76:d4
> inet6 fe80::3e15:c2ff:feba:76d4%en0 prefixlen 64 scopeid 0x4
> inet 192.168.1.214 netmask 0xffffff00 broadcast 192.168.1.255
> inet6 2a00:7660:5c6::3e15:c2ff:feba:76d4 prefixlen 64 autoconf
> inet6 2a00:7660:5c6::b5a5:5839:ca0f:267e prefixlen 64 autoconf temporary
> inet6 2a00:7660:5c6::899 prefixlen 64 dynamic
> nd6 options=1<PERFORMNUD>
> media: autoselect
> status: active
>
> To me it seems that the Macbook has one SLAAC address, one privacy
> extension address and one DHCPv6 managed address.
>
> In fact the CPE manufacturer is a little clever here. They gave me an easy
> address that I can use to access my computer ("899") while still allowing
> SLAAC and privacy extensions. If I want to open ports in my firewall I
> could do that to the "899" address.
>
> But why is my Android devices without IPv6 in this setup?
>
> Regards,
>
> Baldur
>