The recent Erebus attack shows that eclipse attacks with network-Sybil capability against Bitcoin's P2P network are possible. A few Bitcoin protocol tweaks have been quickly implemented to counter the attacks; yet, they are not complete solutions.

We present the Erebus attack, which allows large malicious Internet Service Providers (ISPs) to isolate any targeted public Bitcoin nodes from the Bitcoin peer-to-peer network. The Erebus attack does not require routing manipulation (e.g., BGP hijacks) and hence it is virtually undetectable to any control-plane and even typical data-plane detectors.

About the defenses [Q12] What should I do if I am currently running Bitcoin nodes? You should suspect if you are not receiving new blocks on time. Also, you should wait for Bitcoin Core updates.