I have been burned too many times by address space that looks abundant on paper but collapses under real routing conditions. My current threat model involves verifying whether a provider actually delivers clean legacy IP transit or if they are hiding carrier-grade NAT behind marketing slides. I want to measure latency, packet loss, and path diversity before I allocate any of my own address space to their machines.
What tools exist for this? I know of some public looking glasses, but most only show the upstream perspective, not the last mile. I am unwilling to deploy dual-stack as a compromise if the IPv6 side is an afterthought. NAT is not an option I will tolerate.
How do you validate network quality without first becoming a paying customer?