We wrote a paper [0] in 2015 performing eclipse attacks against Bitcoin. You can watch me talk about it here [1]. At the time it required an attacker with 400 IP addresses. Many of our countermeasures were adopted by Bitcoin-core raising the difficulty of the attack even further. In fact at this very moment I am still working on adding some of our countermeasures to Bitcoin-core [2].
In our attack on Ethereum, only 2 IP addreses were required. We discuss this in our paper:
>"We present new eclipse attacks showing that, prior to the disclosure of this work in January 2018, Ethereum’s peer-to-peer network was significantly less secure than that of Bitcoin. Our eclipse attackers need only control two machines, each with only a single IP address. [..] By contrast, the best known off-path eclipse attacks on Bitcoin [23] require the attacker to control hundreds of host machines, each with a distinct IP address. For most Internet users, it is far from trivial to obtain hundreds (or thousands) of IP addresses. This is why the Bitcoin eclipse attacker envisioned by [23] was a full-fledged botnet or Internet Service Provider, while the BGP-hijacker Bitcoin eclipse attacker envisioned by [17] needed access to a BGP-speaking core Internet router. By contrast, our attacks can be run by any kid with a machine and a script."
-Low-Resource Eclipse Attacks on Ethereum's Peer-to-Peer Network [3]
[0]: https://eprint.iacr.org/2015/263.pdf
[1]: https://www.usenix.org/node/190891