DNS & IP address management

Thu Sep 23 01:45:27 UTC 2021

Many organizations will use their in-addr.arpa zone(s) as an alternative form of poor-man’s IPAM.

It looks like you’ve come across some such organizations.

Likely those are simply the free (unassigned) addresses within the organization. Likely there are other similar host names in other /24s in the same organization if they have more than a /24 of total address space.

OTOH, organizations which do this tend to be relatively small as it doesn’t scale well to multiple administrators managing the same free pool.

Owen

> On Sep 22, 2021, at 07:12 , Joel Sommers <jsommers at colgate.edu> wrote:
> 
> Hello all -
> 
> I am a researcher at Colgate University, working with colleagues at the University of Wisconsin and Boston University on studying aspects of the DNS.
> 
> We're wondering if anyone here would be willing to share some insight into an apparent IP address management practice we have observed that is evident through the DNS.  In particular, we've seen a number of organizations that have a fairly large number of IPv4 addresses (typically all within the same /24 aggregate or similar) all associated with a single FQDN, where the name is typically something like "reserved.52net.example.tld".  Besides the common "reserved" keyword in the FQDN, we also see names like "not-in-use.example.tld", again with quite a few addresses all mapped to that one name.  The naming appears to suggest that this is an on-the-cheap IP address management practice, but we are wondering if there are other operational reasons that might be behind what we observe.
> 
> Thank you for any insights you have -- please feel free to respond off-list.
> 
> Regards,
> Joel Sommers