Entry

Why do I get multiple identical IP addresses returned for some hosts?

Jun 17th, 2001 01:45
Brian Coogan,

Tinydns will return an IP address for each line defining an A record 
and what is happening is that you are defining A records multiple times 
accidentally.  This happens because tinydns data lines generate several 
record types depending on the fields given in each line.  If you take a 
look at the FAQ entry for "What records do the various tinydns data 
lines generate?" you'll see that data lines of the following types all 
generate A records if an IP address is present:  MX ('@'), Child ('&'), 
SOA ('.'), A ('=') and alias ('+').  The problem will be that you have 
multiple definitions for the A record by having more than one line 
containing both a name and an IP address for the host in question.
For instance, this incorrect data:
  .eg.com:1.2.3.4:host.eg.com                 (SOA, NS, A)
  =host.eg.com:1.2.3.4                        (PTR, A)
  @eg.com:1.2.3.4:host.eg.com:10              (MX, A)
actually generates three IP to name mappings for host.example.com and 
thus three A records; tinydns will helpfully return all 3 when asked.  
[Tinydns does this to allow multiple different IP addresses to be 
defined for a host - there are some situations when you might want some 
of the set of IP addresses returned to be the same.]
To correct this situation you need to ensure the IP address ('ip' 
in '.fqdn:ip:x:ttl:timestamp:lo') is only defined in one place.  The 
example above modified to define only a single A record is:
  .eg.com::host.eg.com                        (SOA, NS)
  =host.eg.com:1.2.3.4                        (PTR, A)
  @eg.com::host.eg.com:10                     (MX)
If a name -> address mapping is defined in one place, it is used in the 
whole file, even in references before the actual definition, so once is 
sufficient. [thanks Peter]
To read more about the meaning of the different tinydns data fields 
look at the tinydns-data documentation:
  http://cr.yp.to/djbdns/tinydns-data.html