diff --git a/doc/source/cluster/index.rst b/doc/source/cluster/index.rst
index 224bb2f19..b69cb5134 100644
--- a/doc/source/cluster/index.rst
+++ b/doc/source/cluster/index.rst
@@ -102,6 +102,13 @@ The command will print out the address of the Redis server that was started
 ``<address>`` with the value printed by the command on the head node (it
 should look something like ``123.45.67.89:6379``).
 
+Note that if your compute nodes are on their own subnetwork with Network
+Address Translation, to connect from a regular machine outside that subnetwork,
+the command printed by the head node will not work. You need to find the
+address that will reach the head node from the second machine. If the head node
+has a domain address like compute04.berkeley.edu, you can simply use that in
+place of an IP address and rely on the DNS.
+
 .. code-block:: bash
 
   $ ray start --address=<address> --redis-password='<password>'
@@ -115,11 +122,53 @@ should look something like ``123.45.67.89:6379``).
 If you wish to specify that a machine has 10 CPUs and 1 GPU, you can do this
 with the flags ``--num-cpus=10`` and ``--num-gpus=1``. See the :ref:`Configuration <configuring-ray>` page for more information.
 
+If you see ``Unable to connect to Redis. If the Redis instance is on a
+different machine, check that your firewall is configured properly.``,
+this means the ``--port`` is inaccessible at the given IP address (because, for
+example, the head node is not actually running Ray, or you have the wrong IP
+address).
+
 If you see ``Ray runtime started.``, then the node successfully connected to
-the ``<address>``. If the ``<address>`` is inaccessible (because, for example,
-the head node is not actually running), then you will get an error such as
-``Unable to connect to Redis. If the Redis instance is on a different machine,
-check that your firewall is configured properly.``
+the IP address at the ``--port``. You should now be able to connect to the
+cluster with ``ray.init(address='auto')``.
+
+If ``ray.init(address='auto')`` keeps repeating
+``redis_context.cc:303: Failed to connect to Redis, retrying.``, then the node
+is failing to connect to some other port(s) besides the main port.
+
+.. code-block:: bash
+
+  If connection fails, check your firewall settings and network configuration.
+
+If the connection fails, to check whether each port can be reached from a node,
+you can use a tool such as ``nmap`` or ``nc``.
+
+.. code-block:: bash
+
+  $ nmap -sV --reason -p $PORT $HEAD_ADDRESS
+  Nmap scan report for compute04.berkeley.edu (123.456.78.910)
+  Host is up, received echo-reply ttl 60 (0.00087s latency).
+  rDNS record for 123.456.78.910: compute04.berkeley.edu
+  PORT     STATE SERVICE REASON         VERSION
+  6379/tcp open  redis   syn-ack ttl 60 Redis key-value store
+  Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
+  $ nc -vv -z $HEAD_ADDRESS $PORT
+  Connection to compute04.berkeley.edu 6379 port [tcp/*] succeeded!
+
+If the node cannot access that port at that IP address, you might see
+
+.. code-block:: bash
+
+  $ nmap -sV --reason -p $PORT $HEAD_ADDRESS
+  Nmap scan report for compute04.berkeley.edu (123.456.78.910)
+  Host is up (0.0011s latency).
+  rDNS record for 123.456.78.910: compute04.berkeley.edu
+  PORT     STATE  SERVICE REASON       VERSION
+  6379/tcp closed redis   reset ttl 60
+  Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
+  $ nc -vv -z $HEAD_ADDRESS $PORT
+  nc: connect to compute04.berkeley.edu port 6379 (tcp) failed: Connection refused
+
 
 Stopping Ray
 ~~~~~~~~~~~~