When you're an ISP offering access to the Internet, you need to keep track of a number of things.

• Which address space is assigned to who.
• Forward DNS entries, reverse DNS entries with possible delegation.
• Per-customer consumed bandwidth. This can be useful if a subscriber keeps sucking up transit bandwidth, which may end up being deadly expensive for a small ISP.
• Payment history, in case it's not fully automated already.

Don't forget that subscribers may wish to view/change information themselves (bandwidth graph, DNS delegation, etc).

For all these tasks, you need some kind of software.

• LDAP

• FDN system, written in Perl and only masterable by experienced Gurus
• Ambre, developped in 2013 by Rézine (Eastern France). Ruby on Rails.
• COIN, being developed by Illyse in France. Written in Django, with a generic backend system (for now, OpenVPN backend through LDAP). In English as much as possible, but some French may remain.
• Other tools by FFDN members, in French

This is the process of assigning configuration to the end-user equipment (CPE). This includes IPv4 and IPv6 ranges, DNS servers, NTP servers, and so on.

• Radius is pretty common
• https://en.wikipedia.org/wiki/TR-069