stination_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><h3 id=blackholecluster-metrics>BlackHoleCluster metrics</h3><p>Similar to the PassthroughCluster, this section explains the metrics and the
labels emitted based on the listener t