Support for NU5 on Mainnet will be implemented in zcashd version 5.0.0, which will advertise protocol version 170100.
Backward compatibility in zcashd 
- The minimum peer protocol version that NU5-compatible zcashd nodes will connect to is 170002.
+The minimum peer protocol version that NU5-compatible zcashd nodes will connect to is 170002. They will immediately disconnect from Testnet nodes advertising a peer protocol version less than 170040.
NU5 deployment for zcashd
For each network, approximately 1.5 days (defined in terms of block height) before the corresponding NU5 activation height, nodes compatible with NU5 activation on that network will change the behaviour of their peer connection logic in order to prefer pre-NU5 peers on that network for eviction from the set of peer connections:
diff --git a/zip-0252.rst b/zip-0252.rst index ca4a288a..3af2d2e2 100644 --- a/zip-0252.rst +++ b/zip-0252.rst @@ -156,7 +156,8 @@ Backward compatibility in zcashd -------------------------------- The minimum peer protocol version that NU5-compatible `zcashd` nodes will -connect to is 170002. +connect to is 170002. They will immediately disconnect from Testnet nodes +advertising a peer protocol version less than 170040. NU5 deployment for zcashd -------------------------