title: Google Cloud VM instance SSH connection ~60 seconds timeout with 30 second keepalive
body: <p>I've been connecting to a Google Cloud VM instance via gcloud ssh from my macOS:</p>
  
  <pre><code>$ gcloud compute ssh [username]@[instance]
  </code></pre>
  
  <p>Starting from a week ago, the connection will just drop after ~60 seconds of idle connection and returns:</p>
  
  <pre><code>Connection to [my_external_ip] closed by remote host.
  Connection to [my_external_ip] closed.
  ERROR: (gcloud.compute.ssh) [/usr/bin/ssh] exited with return code [255].
  </code></pre>
  
  <p>I configured the TCP keepalive time to 30 seconds on both my macbook and the VM. But that did not solve the problem. </p>
  
  <p>Any idea how do I extend the connection duration?</p>