21.Can I start a Managed Server if the Administration Server is unavailable?
By default, if a Managed Server is unable to connect to the specified Administration Server during startup, it can retrieve its configuration by reading a configuration file and other files directly. You cannot change the server's configuration until the Administration Server is available. A Managed Server that starts in this way is running in Managed Server Independence mode. For more information, see Starting a Managed Server When the Administration Server Is Not Accessible in Configuring and Managing WebLogic Server.
22.What is the function of T3 in WebLogic Server?
T3 provides a framework for WebLogic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of WebLogic Server clusters and HTTP and other product tunneling. T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications. T3 is a superset of Java Object. Serialization or RMI; anything you can do in Java Object Serialization and RMI can be done over T3. T3 is mandated between WebLogic Servers and between programmatic clients and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and WebLogic Server. It depends on what you want to do. For example: when you want to communicate between a browser and WebLogic Server -- use HTTP, or an ORB and WebLogic Server-IIOP.
23.What is the easiest way to set the classpath?
WebLogic Server installs the following script that you can use to set the classpath that a server requires:
WL_HOME\server\bin\setWLSEnv.cmd (on Windows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX)

Where WL_HOME is the directory in which you installed WebLogic Server. For more information, see "Setting the Classpath" in the WebLogic Server Command Reference.
24.How do I edit the config.xml file?
The persistent configuration for a domain of WebLogic Servers and clusters is stored in an XML configuration file (config.xml). You can modify this file in the following ways:

Using the Administration Console.
If you want to create scripts that automate domain management, use the weblogic.Admin utility. See "weblogic.Admin Command-Line Reference".
If you want to create Java-based management applications, use the Java Management Extensions (JMX) Application Programming Interface (API). See the Programming WebLogic Management Services with JMX guide.
If you want to edit the config.xml file directly (not recommended), see the BEA WebLogic Server Configuration Reference.

25.Is there a quick way to create and start a remote Managed Server?
The recommended approach is to use the Domain Configuration Wizard, as described in "Setting Up and Starting Managed Servers on a Remote Machine" in Creating WebLogic Configurations Using the Configuration Wizard at http://download.oracle.com/docs/cd/E13196_01/platform/docs81/confgwiz/multi.html.
For a streamlined approach, follow the instructions at "Starting Managed Servers From a WebLogic Server Script" in the Administration Console Online Help.

26.The Tree View pane of the WebLogic Console is not visible in my browser. How do I enable it?

Enable the Sun Java Plug-In from the control panel.

27.What is the importance of the Boot Identity file and how will you create it?

If you create boot identity file, it will not ask the user name and password at server startup time.
Create a file called boot.properties in the <DOMAIN_HOME>\servers\<server_name>\security directory that contains two lines:

username=username
password=password

The first time you start the server; the server reads the Boot Identity file and overwrites it with an encrypted version of the username and password.
Thereafter, the server remembers the credentials for subsequent startup cycles.

28.What is the MSI mode in Weblogic? How can you enable and disable this option?

MSI is nothing but Managed Server Independence.
By default, Managed Servers can function independently of the Administration Server.
A Managed Server instance can start in MSI mode if the Administration Server is unavailable.
Configure MSI mode from the Administration Console.
To start a Managed Server in MSI mode, perform the following:

Ensure that the Managed Server’s root directory contains the config subdirectory.
If the config subdirectory does not exist, copy it from the Administration Server’s root directory.
Start the Managed Server at the command line or by using a script.

Environment > Servers > Server_Name > Tuning > Advanced > Managed Server Independence Enabled check box.

29.If the Administration server not available while starting the Managed server which is already enabled MSI, what are the files it will look for?

If the Administration Server is unavailable at boot time, Managed Servers search for:

config.xml
SerializedSystemIni.dat
boot.properties(optional)

Each Managed Server looks in its local config directory for config.xml, a replica of the domain’s config.xml.
You cannot change the configuration of the Managed Server that is running in MSI mode until it restores communication with the Administration Server.

30.What if Administration server goes down? What is the behavior of the managed servers? What are all the things will available or not available?

The Administration Server:

Can go down without affecting the operation of the Managed Servers
Can be restarted when the Managed Servers are still running

When an Administration Server goes down:

The domain log entries are unavailable while it is down
Managed Servers can start in independent mode
The Administration Console and the management tools are unavailable