se, <code>destination_service_name</code> is set to PassthroughCluster and
the <code>destination_ip</code> is set to the IP address of the external service.
The <code>destination_ip</code> label can be used to do a reverse DNS lookup and
get the host name of the external service. As this cluster is passthrough,
other TCP related metrics like <code>istio_tcp_connections_opened_total</code>,
<code>istio_tcp_received_bytes_total</code> and <code>istio_tcp_sent_bytes_total</code> are also
updated.</p></li></ul>