   There are two cases that can cause the "dangling CNAME" message
   to appear:

     * When a CNAME points to an external host name.
     * When a CNAME is misspelled or the host the CNAME points
       to is misspelled

  CNAMEs pointing to external host names

   Sometimes, people may wish to have local names point to external
   entries with CNAME records. For example, it may be desirable to
   have the shortcut "google" for "www.google.com". One way one may
   wish to do this is as follows:

         google.example.com. +86400 CNAME www.google.com.

   MaraDNS' default configuration will not complete the record. In
   other words, some people may expect Mara to output the following
   for "google.example.com":

         google.example.com. +86400 CNAME www.google.com.
         www.google.com. +900 A 66.102.7.104

   Instead, Mara simply outputs:

         google.example.com. +86400 CNAME www.google.com.

   I call this a "dangling CNAME record", since the CNAME record is
   not resolvable by some stub resolvers. In order to resolve
   dangling CNAME records, MaraDNS can be configured thusly:

     * We run two servers of MaraDNS on two different IPs.
     * For the sake of this example, we will suppose that the
       server people send queries to for resolving hostnames has
       the IP 192.168.1.1. We will further suppose that there is a
       server which has the dangling CNAME issue with the IP
       192.168.1.2
     * Set up 192.168.1.1 to use 192.168.1.2 as an upstream server
       by the use of the upstream_servers mararc variable.
     * Set up 192.168.1.2 to be both an authoritative and recursive
       DNS server, and have dangling CNAME records in the
       authoritative half.

   This will cause dangling CNAME records to be fully resolved;
   here is what the two MaraDNS servers do to resolve such a
   record:

    1. A stub resolver asks 192.168.1.1 the IP address for, say
       "google.example.com"
    2. 192.168.1.1 asks 192.168.1.2 the IP address for
       "google.example.com"
    3. 192.168.1.2 tells 192.168.1.1 "google.example.com is a CNAME
       for www.google.com, and I don't have an IP for it"
    4. 192.168.1.1, seeing that it has a CNAME without an IP, asks
       192.168.1.2 the IP for "www.google.com"
    5. 192.168.1.2 recursively resolves the IP for www.google.com,
       and gives this IP for 192.168.1.1
    6. Now that 192.168.1.1 has a complete record, it will send
       this record to the stub resolver. In other words,
       192.168.1.1 will tell the stub resolver that
       google.example.com is a CNAME for www.google.com, and then
       give out the IP for www.google.com.

   Here is an example mararc file for 192.168.1.1:

 ipv4_bind_addresses = "192.168.1.1"
 chroot_dir = "/etc/maradns"
 recursive_acl = "192.168.1.0/24"
 upstream_servers = "192.168.1.2"

   Here is an example mararc file for 192.168.1.2:

 ipv4_bind_addresses = "192.168.1.2"
 chroot_dir = "/etc/maradns"
 recursive_acl = "192.168.1.1"
 csv2 = {}
 csv2["example.com."] = "db.example.com"

   If dangling CNAMEs are not an issue for a given setup, or if
   they are resolved by the above setup with two instances of
   MaraDNS, the warnings about dangling CNAMEs can be turned off by
   adding this to a mararc file:

 no_cname_warnings = 1

  A typo can cause a dangling CNAME record

   A typo can also cause a dangling CNAME record. E.g:

 www.example.com. CNAME hoost1.example.com.
 host1.example.com. A 10.1.2.3

   Here, we mispelled the CNAME record; we meant to type
   "host1.example.com" but typed in "hoost1.example.com". We can
   also get a dangling CNAME thusly:

 www.example.com. CNAME host1.example.com.
 hoost1.example.com. A 10.1.2.3

   Or by a typo in the mararc file:

 csv2["exammple.com."] = "db.example.com"

   (We typed in exammple.com when we should have typed in
   "example.com")

   Followed by a zone file that looks like this:

 www.example.com. CNAME host1.example.com.
 host1.% A 10.1.2.3

   Since the % will expand to "exammple.com" instead of
   "example.com".

   In all of these cases, the dangling CNAME warning will go away
   when the typo is found and corrected.
