private Stream<HostName> findUnusedHostnames(NodeList nodes) {
            Set<String> usedHostnames = nodes.stream().map(Node::hostname).collect(Collectors.toSet());
            return hostnames.stream().filter(hostname -> !usedHostnames.contains(hostname.value()));
        }
Finds all unused IP addresses in this pool

@param nodes a list of all nodes in the repository
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java