Can two directly peered Bitcoin nodes temporarily diverge onto different chain tips?
Question
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?
Answer 1
Yes, they will temporarily diverge. Each node will keep its own tip until it sees a longer chain. Since both Y and Z have the same work, the tie won't break until a miner finds the next block on top of either Y or Z. When that happens, the node on the losing side will reorg to the longer chain.