Re: DNS & IP address management

[Owen DeLong via NANOG <nanog () nanog org>]

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 () 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