I know blockchain but I'm really a noob for all internet techs.
My question is simple but not too simple to put in words. Can nodes communicate between each others so they know for sure who they receive message from if the sender wants to be known? (I add the "if the sender..." because theoretically nodes could hide themselves and send anonymously)
Can a node require other nodes to sign their messages. Do they actually do it?
Do they use another technique than signing to be sure who they're communicating with? like I send a code to the address of a node and this node as to send the code back with its message.

If someone malevolent attacks all the nodes at ounce by sending many messages to the nodes.  Would they need to all change their addresses and find each other again?