On Tue, 24 Oct 2017, Nick Hilliard wrote: (...)
I'd politely suggest that this is an area that the RIPE NCC should not get involved in, especially from the point of view of implicitly issuing recommended practice by implying that there is a problem with doing this. The IXP associations are better placed to gather consensus for creating best practices, and there is no general consensus in the IXP community on this issue.
As regards using this as a metric for determining whether an ixp address assignment is being used for legitimate purposes, I'd suggest that this is of only marginal use at best. By all means run a port scan to see if there is any obvious mis-use (e.g. services listening on www/smtp/etc), but the presence or absence of the route in the dfz doesn't mean anything one way or another.
Nick CTO, INEX
+1. I only have some doubts about running (regular) portscans. Cheers, Carlos