Every ISP has an IPAM. For a worrying number of operators, it is a spreadsheet named IP_addresses_FINAL_v3.xlsx, last reliably updated by someone who no longer works there. IP address management sounds like a solved, boring problem - until two customers get the same static /32, or you discover mid-audit that nobody knows what lives in half of a /23.
This is an honest comparison of the real options in 2026, written from the ISP operator's chair - because most IPAM comparisons are written for enterprise IT, and an ISP's needs are meaningfully different.
What an ISP actually needs from IPAM
Enterprise IPAM tracks which server has which address. ISP IPAM has a harder job, because addresses are inventory that generates revenue:
- Subnets and pools by function - CGNAT pools (100.64.0.0/10 done right), public dynamic pools, static assignment blocks, infrastructure ranges, IPv6 prefix-delegation space
- Assignment tied to subscribers - who holds 203.0.113.42, since when, on which plan, and is it billed as an add-on
- Integration with provisioning - the address a subscriber should have and the one RADIUS actually hands out must be the same fact, not two databases drifting apart
- IPv6 as a first-class citizen - per-subscriber delegated prefixes, not just "we have a /32 somewhere"
Hold every candidate against that list and the field sorts itself quickly.
phpIPAM - the default self-hosted answer
The workhorse: free, open-source, PHP/MySQL, subnets, VLANs, VRFs, ping-based discovery, an API, and years of production mileage. If your goal is documenting address space, phpIPAM does it well.
Its limits from an ISP chair: it is fundamentally a documentation system. It knows a subnet exists and that an address is marked "used" - it does not know the address belongs to a paying subscriber whose invoice is overdue, and it will not tell RADIUS anything. Keeping phpIPAM synchronized with your billing system and your RADIUS reality is a manual process or a custom-scripts project, and drift is the default failure mode. The interface has also aged, which matters when technicians are supposed to update it in the field (they will not).
Right fit: documenting infrastructure ranges; teams with scripting appetite and a separate source of truth for subscribers.
NetBox - infrastructure source of truth, not subscriber IPAM
NetBox is the darling of network engineering teams, and deservedly - racks, devices, cables, circuits, prefixes, and a first-class API make it the best infrastructure modeling tool on this list. Large ISPs absolutely should model their core network in it.
But NetBox is explicitly a source-of-truth for infrastructure intent, not a subscriber management system. Ten thousand residential customers with dynamic pool assignments, statics as billable add-ons, and prefix delegations are not what its data model is for - you would be building the ISP layer yourself on top. It is also a heavier self-hosted commitment (Python stack, migrations, upgrades) than small-team operators usually want to own.
Right fit: modeling towers, routers, and transit at engineering-driven ISPs - alongside, not instead of, subscriber IPAM.
Windows Server IPAM and enterprise suites
Microsoft's IPAM ships with Windows Server and manages Microsoft DHCP/DNS estates. The commercial DDI suites (Infoblox, BlueCat and friends) are excellent and priced for banks. Neither category understands PPPoE sessions, RADIUS pools, or subscribers, and the DDI suites cost more per year than a small ISP's entire software budget.
Right fit: the corporate IT network at a large ISP; not the access network.
Spreadsheets - the honest baseline
Free, flexible, and the single most common IPAM in the industry. Also: no validation (nothing stops two rows claiming one address), no history, no API, no connection to what RADIUS actually does, and a bus factor of one. Every horror story in this niche - duplicate statics, blackholed ranges, the /24 nobody dares touch - traces back to a spreadsheet that was authoritative right up until it silently was not.
IPAM built into the ISP platform - ISPbox
The structural problem with every option above is the same: IPAM lives apart from the systems that consume addresses. The fix is not a better standalone database - it is IPAM that shares a brain with subscribers, billing, and provisioning. That is how IPAM in ISPbox works:
- Pools and subnets are defined once, and the RADIUS/PPPoE layer assigns from them directly - documentation and reality cannot drift, because they are the same record.
- A static IP is a subscriber attribute and a billable add-on: sell it in the portal, and it provisions on the next session (or live via CoA) and appears on the invoice.
- IPv6 prefix delegation is managed per subscriber alongside IPv4, not in a parallel spreadsheet.
- When a customer churns, their addresses return to the pool automatically - no orphaned "reserved" rows aging into folklore.
The trade-off, stated plainly: ISPbox's IPAM is subscriber-and-access-network IPAM. If you want to model every patch cable in a datacenter, NetBox does that better - and pairing NetBox (infrastructure) with ISPbox (subscribers, pools, billing) is a genuinely good architecture for larger operators.
The verdict
- Documenting infrastructure, comfortable self-hosting: phpIPAM
- Engineering-grade infrastructure modeling: NetBox
- Microsoft corporate estate: Windows Server IPAM
- Subscriber addresses at an ISP - pools, statics, PD, billing: an integrated platform. That is ISPbox, from $25/month with IPAM, RADIUS provisioning, billing, and the customer portal in every plan.
And whichever you choose: retire the spreadsheet this quarter, while its errors are still small.
FAQ
What is the best free IPAM tool? phpIPAM is the most established free self-hosted option for general address documentation; NetBox is the stronger choice for modeling network infrastructure. Neither ties addresses to subscribers or billing - that requires an ISP platform.
What is the difference between IPAM and DHCP? DHCP hands out addresses at connection time; IPAM is the system of record for which ranges exist and who holds what. In ISP practice the two must stay synchronized, which is why integrated assignment beats standalone documentation.
Do small ISPs need IPAM software? Yes - earlier than most expect. Duplicate static assignments and undocumented ranges start causing outages and audit pain well below 500 subscribers, and migrating off a spreadsheet only gets harder with size.
Can IPAM handle IPv6 prefix delegation? Standalone tools track IPv6 subnets, but per-subscriber prefix delegation is an assignment decision made at session time - it belongs in the platform that drives RADIUS, which is how ISPbox manages it.
