Suppose two Bitcoin nodes, A and B, are directly peered, and each also has additional peers:
A → B, C, D
B → A, E, F
Assume both nodes are currently at block X.
Now imagine two miners produce competing blocks Y and Z at the same height. Block Y reaches node A first (via C), and block Z reaches node B first (via E). While A is validating Y, B is validating Z, resulting in:
Node A: X ← Y
Node B: X ← Z
Both chains have the same amount of work because blocks Y and Z have equal difficulty. Now, when the nodes A and B exchange blocks Y and Z, will they update their tips or just hold on those blocks until one chain becomes longer than the other?
