IPv6 DNS Part 3 (authoritative DNS via IPv6 transport)

In this post I’ll finish off DNS by ensuring that I have publicly accessible IPv6 DNS servers. As I pointed out in the first two IPv6 posts, there are three parts of getting to “IPv6 DNS”:

  1. The first is to get AAAA (quad-A) records into your DNS system. At that point clients can ask for the AAAA records over IPv4 and everything will work just fine.
  2. The second is for you to actually serve your DNS zones over IPv6.
  3. The third is to get hooked into the global IPv6 DNS system, so that you (and others) can resolve your IPv6 addresses.

In this post, we will deal with the third part, ensuring that all the DNS servers needed to resolve my AAAA records are IPv6 capable. This step isn’t strictly necessary since, as I pointed out before, there’s nothing wrong with serving your AAAA records via IPv4.

First, let’s take a look at the symptoms of my problem:

$ dig -6 +short +trace ipv6.thuktun.org aaaa
 ;; connection timed out; no servers could be reached

What has happened here is that there is no authoritative DNS server that can be reached via IPv6. So, what’s the problem?

One thing that I’ve never mentioned is that “my” local DNS server is a hidden master. It holds all the zone files, but is not advertised. My advertised public DNS servers are elsewhere, and they pick up my zone data via AXFR whenever I make changes and they are sent a NOTIFY. So, while my local server has all the zone data, it will never be queried during a normal DNS lookup. The advertised DNS servers, the slaves, actually serve all the answers.

It turns out that there are two problems here:

  1. My external slave name servers aren’t IPv6 capable;
  2. My resolv.conf has no IPv6 name servers listed.

My external nameservers are run by a friend at his organization’s datacenter. They aren’t prepared to serve DNS over IPv6, and won’t be any time soon. The fastest way to fix this is to move my external DNS to a DNS hosting provider that is IPv6 capable. Fortunately, I can get IPv6 DNS from the same place that I get my IPv6 tunnel: Hurricane Electric.

Using their DNS slave server setup page, I can easily make Hurricane’s DNS servers be my public slave DNS servers. I do have to ensure that their DNS servers can do zone transfers from my hidden master, which is mostly handled by using the the allow-transfer statement in my Bind config files, which is left as an exercise for the student.

After setting up the slave servers at Hurricane, I can wait for them to zone transfer my data to their servers. This can take 5-10 minutes for the first transfer.

At this point, there are three completely independent sets of name servers that have correct data for my domain:

  1. My home hidden master
  2. The current advertised DNS servers at my friend’s organization
  3. The as-yet unadvertised DNS servers at Hurricane Electric

All that remains is to remove the advertisements for the “old” servers and to add advertisements for the new servers. This is done at your domain registrar. Fortunately, my registrar is Register4Less, and their DNS system can take IPv6 addresses. In fact, it was easier than I expected. Unlike some other registrars I’ve used in the past, at Register4Less, you enter the names of your DNS servers, not the IP addresses. Register4Less resolved the hostnames ns1-ns5.e.net and created NS records for both the IPv4 and IPv6 addresses.

There’s still one step left, and that’s to add some IPv6 name servers to my resolv.conf file.  I could use the five DNS servers that Hurricane Electric has advertised, but I’ll go one step farther. I’ll use the anycast DNS server address that Hurricane gave me when I established my tunnel:

$ more /etc/resolv.conf
nameserver                     ;; IPv4 nameservers from my ISP
nameserver 2001:470:20::2                 ;; IPv6 anycast name server from HE.NET

And now here’s a full “trace” of IPv6 DNS resolution:

$ dig -6 +trace ipv6.thuktun.org aaaa

; <<>> DiG 9.7.3 <<>> -6 +trace ipv6.thuktun.org aaaa
;; global options: +cmd
.            79981    IN    NS    g.root-servers.net.
.            79981    IN    NS    j.root-servers.net.
.            79981    IN    NS    a.root-servers.net.
.            79981    IN    NS    i.root-servers.net.
.            79981    IN    NS    h.root-servers.net.
.            79981    IN    NS    l.root-servers.net.
.            79981    IN    NS    c.root-servers.net.
.            79981    IN    NS    b.root-servers.net.
.            79981    IN    NS    d.root-servers.net.
.            79981    IN    NS    m.root-servers.net.
.            79981    IN    NS    f.root-servers.net.
.            79981    IN    NS    e.root-servers.net.
.            79981    IN    NS    k.root-servers.net.
;; Received 509 bytes from 2001:470:20::2#53(2001:470:20::2) in 31 ms

org.            172800    IN    NS    b0.org.afilias-nst.org.
org.            172800    IN    NS    a2.org.afilias-nst.info.
org.            172800    IN    NS    d0.org.afilias-nst.org.
org.            172800    IN    NS    c0.org.afilias-nst.info.
org.            172800    IN    NS    a0.org.afilias-nst.info.
org.            172800    IN    NS    b2.org.afilias-nst.org.
;; Received 436 bytes from 2001:7fe::53#53(i.root-servers.net) in 157 ms

thuktun.org.        86400    IN    NS    ns5.he.net.
thuktun.org.        86400    IN    NS    ns4.he.net.
thuktun.org.        86400    IN    NS    ns2.he.net.
thuktun.org.        86400    IN    NS    ns3.he.net.
;; Received 112 bytes from 2001:500:c::1#53(b0.org.afilias-nst.org) in 188 msipv6.thuktun.org.    28800    IN    AAAA    2001:470:67:84::10
;; Received 62 bytes from 2001:470:500::2#53(ns5.he.net) in 28 ms

And I’m done with DNS. Now I can go on to some other services, like SSH, FTP, HTTP, etc.

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  1. #1 by Kimani on June 15, 2012 - 1:09 am

    I am configuring a DNS server in linux (Fedora) in a lab environment. I am wondering if it is possible to have IPv6 as a standalone address. At the moment it works only if both IPv4 and IPv6 are enabled. Please advice..

    Here is an image for reference: http://i47.tinypic.com/ih5fyf.png

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