Hi Mark,
yes, we want to send to ES-nodes. We have multiple network interfaces on the machine where Metricbeats is running. And just a particular one can reach the Elasticsearch node.
To communicate via curl from the machine where the Metricbeats is installed to the ES node it would be for instance work with:
curl --interface 10.30.150.32 -XGET http://10.30.134.155:9200/_cat/indices