Add some DSN clarifications

Author: David Engel

docs/connect/odbc/linux-mac/connection-string-keywords-and-data-source-names-dsns.md

@@ -2,7 +2,7 @@
 title: "Connecting using ODBC"
 description: "Learn how to create a connection to a database from Linux or macOS using the Microsoft ODBC Driver for SQL Server."
 ms.custom: ""
-ms.date: "01/19/2017"
+ms.date: "05/11/2020"
 ms.prod: sql
 ms.prod_service: connectivity
 ms.reviewer: ""
@@ -16,7 +16,9 @@ ms.assetid: f95cdbce-e7c2-4e56-a9f7-8fa3a920a125
 author: David-Engel
 ms.author: v-daenge
 ---
+
 # Connecting to SQL Server
+
 [!INCLUDE[Driver_ODBC_Download](../../../includes/driver_odbc_download.md)]
 
 This topic discusses how you can create a connection to a [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)] database.  
@@ -30,34 +32,40 @@ See [DSN and Connection String Keywords and Attributes](../dsn-connection-string
   
 The value passed to the **Driver** keyword can be one of the following:  
 
--   The name you used when you installed the driver.
+- The name you used when you installed the driver.
 
--   The path to the driver library, which was specified in the template .ini file used to install the driver.  
+- The path to the driver library, which was specified in the template .ini file used to install the driver.  
 
-To create a DSN, create (if necessary) and edit the file **~/.odbc.ini** (`.odbc.ini` in your home directory) for a User DSN only accessible to the current user, or `/etc/odbc.ini` for a System DSN (administrative privileges required.) The following is a sample file that shows the minimal required entries for a DSN:  
+DSNs are optional. You can use a DSN to define connection string keywords under a `DSN` name that you can then reference in the connection string. To create a DSN, create (if necessary) and edit the file **~/.odbc.ini** (`.odbc.ini` in your home directory) for a User DSN only accessible to the current user, or `/etc/odbc.ini` for a System DSN (administrative privileges required.) The following is a sample file that shows the minimal required entries for a DSN:  
 
-```  
+```ini
+# [DSN name]
 [MSSQLTest]  
-Driver = ODBC Driver 13 for SQL Server  
-Server = [protocol:]server[,port]  
-#   
+Driver = ODBC Driver 17 for SQL Server  
+# Server = [protocol:]server[,port]  
+Server = tcp:localhost,1433
+#
 # Note:  
 # Port is not a valid keyword in the odbc.ini file  
 # for the Microsoft ODBC driver on Linux or macOS
 #  
 ```  
 
+To connect using the above DSN in a connection string, you would specify the `DSN` keyword like: `DSN=MSSQLTest;UID=my_username;PWD=my_password`  
+The above connection string would be the equivalent of specifying a connection string without the `DSN` keyword like: `Driver=ODBC Driver 17 for SQL Server;Server=tcp:localhost,1433;UID=my_username;PWD=my_password`
+
 You can optionally specify the protocol and port to connect to the server. For example, **Server=tcp:**_servername_**,12345**. Note that the only protocol supported by the Linux and macOS drivers is `tcp`.
 
 To connect to a named instance on a static port, use <b>Server=</b>*servername*,**port_number**. Connecting to a dynamic port is not supported before version 17.4.
 
 Alternatively, you can add the DSN information to a template file, and execute the following command to add it to `~/.odbc.ini` :
  - **odbcinst -i -s -f** _template_file_  
- 
+
 You can verify that your driver is working by using `isql` to test the connection, or you can use this command:
  - **bcp master.INFORMATION_SCHEMA.TABLES out OutFile.dat -S <server> -U <name> -P <password>**  
 
 ## Using TLS/SSL  
+
 You can use Transport Layer Security (TLS), previously known as Secure Sockets Layer (SSL), to encrypt connections to [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)]. TLS protects [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)] user names and passwords over the network. TLS also verifies the identity of the server to protect against man-in-the-middle (MITM) attacks.  
 
 Enabling encryption increases security at the expense of performance.
@@ -73,7 +81,7 @@ Regardless of the settings for **Encrypt** and **TrustServerCertificate**, the s
 
 By default, encrypted connections always verify the server's certificate. However, if you connect to a server that has a self-signed certificate, also add the `TrustServerCertificate` option to bypass checking the certificate against the list of trusted certificate authorities:  
 
-```  
+```
 Driver={ODBC Driver 13 for SQL Server};Server=ServerNameHere;Encrypt=YES;TrustServerCertificate=YES  
 ```