Can I run multiple public mainnet ethereum nodes on different machines that return the same external IP address, on internal home network. What I mean is if I hit this site, http://www.nirsoft.net/show_my_ip_address.php, from all machines they show the same IP address. It appears to work when I run two nodes, but am slightly afraid they will confuse/corrupt each other somehow.
It wont be an issue.
Kademlia nodes communicate among themselves using UDP. A virtual or overlay network is formed by the participant nodes. Each node is identified by a number or node ID. The node ID serves not only as identification, but the Kademlia algorithm uses the node ID to locate values (usually file hashes or keywords). In fact, the node ID provides a direct map to file hashes and that node stores information on where to obtain the file or resource.
Essence is, node discovery is not purely based on IP Address of the host