anyone knows how Russia limited the access?
All ISP providers are required to have black boxes installed on-site. These boxes can do traffic shaping (e.g. Twitter is degraded) and basic filtering based on IP addresses. I think, deep packet inspection is also feasible.
Config updates are pushed centrally to these boxes.
Self-managed VPNs still work.
Or if Twitter gets more IP addresses, they'll work for a short while, until black box config updated?