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.

On Oct 2, 2020, at 2:50 PM, Matt Brennan <brennanma@gmail.com> wrote:

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.

-Matt

On Fri, Oct 2, 2020 at 2:00 PM Matt Hoppes <mattlists@rivervalleyinternet.net> wrote:

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?