diff --git a/main.py b/main.py
index dd51fd5..a72605c 100644
--- a/main.py
+++ b/main.py
@@ -288,7 +288,7 @@ async def cli_loop(sk, pk, chain, mempool, network):
 # Main entry point
 # ──────────────────────────────────────────────
 
-async def run_node(port: int, connect_to: str | None, fund: int, datadir: str | None):
+async def run_node(port: int, host: str, connect_to: str | None, fund: int, datadir: str | None):
     """Boot the node, optionally connect to a peer, then enter the CLI."""
     sk, pk = create_wallet()
 
@@ -326,7 +326,7 @@ async def on_peer_connected(writer):
         await writer.drain()
         logger.info("🔄 Sent state sync to new peer")
 
-    network.set_on_peer_connected(on_peer_connected)
+    network._on_peer_connected = on_peer_connected
 
     await network.start(port=port, host=host)
 
@@ -373,7 +373,7 @@ def main():
     )
 
     try:
-        asyncio.run(run_node(args.port, args.connect, args.fund, args.datadir))
+        asyncio.run(run_node(args.port, args.host, args.connect, args.fund, args.datadir))
     except KeyboardInterrupt:
         print("\nNode shut down.")
 
diff --git a/minichain/p2p.py b/minichain/p2p.py
index ee52d7d..5e4950a 100644
--- a/minichain/p2p.py
+++ b/minichain/p2p.py
@@ -43,7 +43,7 @@ def register_handler(self, handler_callback):
             raise ValueError("handler_callback must be callable")
         self._handler_callback = handler_callback
 
-    async def start(self, port: int = 9000):
+    async def start(self, port: int = 9000, host: str = "127.0.0.1"):
         """Start listening for incoming peer connections on the given port."""
         self._port = port
         self._server = await asyncio.start_server(
@@ -206,7 +206,13 @@ def _validate_block_payload(self, payload):
     def _validate_message(self, message):
         if not isinstance(message, dict):
             return False
-        if set(message) != {"type", "data"}:
+        # Allow _peer_addr field added by _listen_to_peer
+        required_fields = {"type", "data"}
+        if not required_fields.issubset(set(message)):
+            return False
+        # Reject messages with unexpected fields (except _peer_addr)
+        allowed_fields = {"type", "data", "_peer_addr"}
+        if not set(message).issubset(allowed_fields):
             return False
 
         msg_type = message.get("type")