[DOCS] Add loopback to X-Pack install info (elastic/x-pack-elasticsearch#2237)
Original commit: elastic/x-pack-elasticsearch@a809fbfec974ce9e5b1572d615e004532f14226a
@@ -151,8 +151,10 @@ bootstrap password is only intended to be a transient password that is used to
help you set all the built-in user passwords.
--
-.. If you have more than one node, you must configure SSL/TLS for inter-node
-communication. For more information, see
+.. If you have more than one node or a single node that listens on an external
+interface, you must configure SSL/TLS for inter-node communication. Single-node
+instances that use a loopback interface do not have this requirement. For more
+information, see
{xpack-ref}/encrypting-communications.html[Encrypting Communications].
... Generate node certificates. For example, you can use the `certgen` command
line tool to generate a certificate authority and signed certificates for your
