[TriLUG] Understanding why invalid hostnames and short names resolve to my home router IP

[Kristopher Kane]

I have a home network which uses DynDNS.org on my router.

I'm trying to understand what causes an invalid hostname, and short names,
 to return the IP associated with my DynDNS hostname.

For example:

>ping unreachable-host
 resolves back to my router's IP and pongs.


I normally use OpenDNS in my resolv.conf but have tested this with 8.8.8.8
as well.  I only use nameserver entries with no search or domain entries.

I am seeing some inconsistent behavior when I disable the wildcard matching
on my DynDNS account.  If I disable it, then flush the DNS cache on the
Mac, invalid hostnames and short hostnames don't resolve in a ping
(desired).  On some CentOS 6 VMs, within the same home network, they
continue to resolve back to my router's IP.  I'm not aware of any caching
on my part between the VM and the DNS server.  There are no /etc/host
entries that resolve as well.

My desire is that short hostnames should only resolve from a ping if they
are valid in DNS or /etc/hosts.

It seemed like something easy to figure out but I am unable to identify it.


Kris