So I am using Virgin Business but I am posting in here as I assume the issue could affect anyone. I have my Virgin router in modem only mode and I recently replaced the actual router I was using.
Shortly after that users on my network reported very slow loading times on Instagram and Youtube in particular. Some videos would take 30s to load and some would not at all. But all played fine once they had started. Interestingly those using a VPN connection did not have the same issue.
After a lot of debugging with different DNS configurations I found this page which shows you which cache server you are using for googlevideos.com which provides the content for Youtube:
https://redirector.googlevideo.com/report_mapping
The result on that page for my connection showed:
82.39.109.XXX => teleitalia-lin2 (82.39.109.0/24)
And sure enough the googlevideo.com endpoints for the videos were resolving to an ISP in Italy...
I put two and two together and realised after replacing my router the IP address I was being assigned on the WAN had changed and for some reason Google now though my best cache server was in Italy.
Once I switched back to the old router with its MAC address I got another IP and the content issues stopped. The result from the google report mapping was now:
82.34.155.XXX => virginmedia-lcy4 (82.34.144.0/20)
Not sure if Virgin or Google need to update their configuration here?
