3 ms·

Dual stack means twice as much to maintain and twice as much to go wrong.

eqvinox 5y ago
It also means twice as much can go right. I've been able to rescue a broken IPv4 config via IPv6 access several times, and vice versa.
magicalhippo 5y ago
> twice as much to go wrong Actually it's more than that, given that extra services like DNS are pretty much required these days and that DHCP has been replaced with two things, RA and DHCPv6, instead of just one. As a concrete example, I run split-horizon DNS for an internal service I want Let's Encrypt certificates for. This was trivial to set up and worked great from my desktop computer, but for some reason my service didn't work with my phone. Turns out Android refuses to use provided IPv4 DNS addresses if it got allocated an IPv6 address, and reverts to Google's own DNS servers.
- jeroenhd 5y ago
  > Turns out Android refuses to use provided IPv4 DNS addresses if it got allocated an IPv6 address, and reverts to Google's own DNS servers. That's strange, I haven't seen this happen to my devices at all, and my pihole is IPv4 only for now. From what I can find online, it seems that this happens when Android is configured with an IPv6 address but the provided DNS server won't resolve AAAA queries. Allowing your DNS server to look up AAAA addresses would probably fix your problem?
  - magicalhippo 5y ago
    > Allowing your DNS server to look up AAAA addresses would probably fix your problem? I'm running Pi-Hole as well, and I don't have an issue with AAAA records as far as I can determine. I found several forum posts suggesting I make my router hand out the IPv6 address to my DNS server (also Pi-Hole) and after I did that it started working right away.
  - midasuni 5y ago
    I think the problem is you have www.somesite.com which resolves publicly to an A and AAAA record, and you override its A record with a local DNS entry, but not its AAAA entry? Sounds like an Android bug if you NXdomain the AAAA entry and it still insists on using it (or it overrides your DNS server and goes to a google one)
    - jeroenhd 5y ago
      I couldn't find the code that does this in my cursory check of the Android source code, but I think it's a misconfiguration check that's failing. That's the feeling I get from others reporting similar issues on help forums, anyway. I think Android sees a world routable IP address, notices it has connectivity and then finds out the DNS server doesn't return IPv6 addresses for known IPv6 capable hosts (such as Google.com). That seems like a fair way to detect misconfiguration to me, though I would've put up a notification warning about the switchover so users can get someone to fix their issue.

It also means twice as much can go right. I've been able to rescue a broken IPv4 config via IPv6 access several times, and vice versa.

magicalhippo 5y ago

> twice as much to go wrong Actually it's more than that, given that extra services like DNS are pretty much required these days and that DHCP has been replaced with two things, RA and DHCPv6, instead of just one. As a concrete example, I run split-horizon DNS for an internal service I want Let's Encrypt certificates for. This was trivial to set up and worked great from my desktop computer, but for some reason my service didn't work with my phone. Turns out Android refuses to use provided IPv4 DNS addresses if it got allocated an IPv6 address, and reverts to Google's own DNS servers.

jeroenhd 5y ago
> Turns out Android refuses to use provided IPv4 DNS addresses if it got allocated an IPv6 address, and reverts to Google's own DNS servers. That's strange, I haven't seen this happen to my devices at all, and my pihole is IPv4 only for now. From what I can find online, it seems that this happens when Android is configured with an IPv6 address but the provided DNS server won't resolve AAAA queries. Allowing your DNS server to look up AAAA addresses would probably fix your problem?
- magicalhippo 5y ago
  > Allowing your DNS server to look up AAAA addresses would probably fix your problem? I'm running Pi-Hole as well, and I don't have an issue with AAAA records as far as I can determine. I found several forum posts suggesting I make my router hand out the IPv6 address to my DNS server (also Pi-Hole) and after I did that it started working right away.
- midasuni 5y ago
  I think the problem is you have www.somesite.com which resolves publicly to an A and AAAA record, and you override its A record with a local DNS entry, but not its AAAA entry? Sounds like an Android bug if you NXdomain the AAAA entry and it still insists on using it (or it overrides your DNS server and goes to a google one)
  - jeroenhd 5y ago
    I couldn't find the code that does this in my cursory check of the Android source code, but I think it's a misconfiguration check that's failing. That's the feeling I get from others reporting similar issues on help forums, anyway. I think Android sees a world routable IP address, notices it has connectivity and then finds out the DNS server doesn't return IPv6 addresses for known IPv6 capable hosts (such as Google.com). That seems like a fair way to detect misconfiguration to me, though I would've put up a notification warning about the switchover so users can get someone to fix their issue.