IPv4 Mismanagement

I'm sitting here in the office on a Friday performing some IP maintenance and I see that one of our upstreams is still filtering an IP range we haven't used in years. I dig into it a bit more and it turns out a major carrier still has them SWIPed to us.

This got me curious and I dug more into IPs from back in our early days and discovered there are two Tier-1 carriers we no longer do business with that still have large blocks of their own IPs SWIPED and allocated to us.

This is really confusing and concerning. I know it's not the end-all-be-all, but I wonder how much IPv4 exhaustion is being caused by this type of IPv4 mis-management, where IPs are still shown as "allocated" to a customer who hasn't used them in years.

I've seen this behavior from Frontier and CenturyLink to name just a few.

Any thoughts on this?

A service I disconnected more than 2 years ago still has a /24 of their space SWIPED to me. Their NOC closed the ticket I opened to remove. Unknown if it’s actually in use for another customer.

I also had a conversation last week with another ISP (we were renegotiating our contract) about this. The order form they sent me had multiple /28’s we had “given back” years ago still listed. Turns out they’re still being routed to us as well.

I would bet it happens all over the place.


I have the same thing with a service that was disconnected a couple years ago. Four IP blocks of /24 size are still swipped to us and we’re announcing them. I don’t put any customers on them and just use them for temporary things for fear that some day someone will want them back.

I suspect many providers don’t have good business processes for reclaiming IP space that was assigned to customers who have either disconnected or voluntarily returned the space.

The provider I started out with in the mid/late 90s bootstrapped itself with IP space from MCI (now, CenturyLink… I think?) and UUNET (now Verizon Business), but we handed those blocks back when we started getting provider-independent space from ARIN. No idea what became of that space after we stopped announcing it.


Groups that have such things I can only presume do not do a good job
of periodically going through and auditing their IP allocations or, if
they do, then they don't do a good enough job of cleaning up all the

It is a long-winded, laborious, thankless task (well, mostly thankless)
and we should be writing software to do it for us. Of course, we all
know how bad everyone is at that, ergo it isn't often done.

On the other hand, perhaps these ISPs are worried that they might be
audited by an RIR?

It is a thankless task, but something that becomes increasingly important as $provider starts to run low on IPv4 space to assign to customers.

Thank you