   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 = "/opt/local/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 = "/opt/local/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.
