android$ nslookup www.kame.net Server: 192.168.0.2 Address 1: 192.168.0.2 Name: www.kame.net Address 1: 2001:200:dff:fff1:216:3eff:feb1:44d7 Address 2: 18.104.22.168 orange.kame.net
wheezy$ nslookup www.kame.net Server: 192.168.0.2 Address: 192.168.0.2#53 Non-authoritative answer: www.kame.net canonical name = orange.kame.net. Name: orange.kame.net Address: 22.214.171.124
And host v9.8.4 has it the other way around:
wheezy$ host www.kame.net www.kame.net is an alias for orange.kame.net. orange.kame.net has address 126.96.36.199 orange.kame.net has IPv6 address 2001:200:dff:fff1:216:3eff:feb1:44d7
Glibc returns the AAAA record:
wheezy$ getent hosts www.kame.net 2001:200:dff:fff1:216:3eff:feb1:44d7 orange.kame.net www.kame.net
- MacOS 10.7.5 seems to behave like Linux here
- there's no host(1) utility on Android!
The kernel configuration differs only slightly:
$ sysctl -a -r ipv6 | egrep -v '(conf|neigh)\.(wlan|ip6tnl0|sit0|rmnet|dummy|lo|default|eth0)' $ diff out.wheezy out.android 6c6,7 < net.ipv6.conf.all.accept_redirects = 0 --- > net.ipv6.conf.all.accept_ra_rtr_pref = 1 > net.ipv6.conf.all.accept_redirects = 1 18c19 < net.ipv6.conf.all.ndisc_notify = 0 --- > net.ipv6.conf.all.optimistic_dad = 0 20a22 > net.ipv6.conf.all.router_probe_interval = 60 28,29c30,31 < net.ipv6.ip6frag_high_thresh = 4194304 < net.ipv6.ip6frag_low_thresh = 3145728 --- > net.ipv6.ip6frag_high_thresh = 262144 > net.ipv6.ip6frag_low_thresh = 196608 41a44 > net.ipv6.xfrm6_gc_thresh = 2048
gai.conf has not been changed on the wheezy system (and is not present on Android):
wheezy$ grep ^[a-z] /etc/gai.conf precedence ::ffff:0:0/96 100
But this only controls resolver should alter the output of dnsutils, but it did not:which seems to be fine for Linux. Changing the
wheezy$ cat /etc/resolv.conf domain example.org nameserver 192.168.0.2 options inet6
Still, host returns the A record first on Linux / MacOS X.
What I really like to do is disable IPv6 for certain addresses: some hosts have an AAAA record but are not reachable via IPv6. Some applications do not detect this and try to contact their AAAA record until a timeout is reached.
- Android only queries for AAAA records in IPv4 network without default route
- HTTPS won't fall back from IPv6 to IPv4
- Mail does not fall back from IPv6 to v4 in an v6 network