Citrix Interview Q&A prepared by Ravi...!

1.       What will be happen if LHC corrupted?

http://support.citrix.com/article/CTX759510

- You can not access application from that server.
- IMA will not start
- recreating LHC will fix the issue

Each XenApp server stores a subset of the data store in the Local Host Cache (LHC). The LHC performs two primary functions:

• Permits a server to function in the absence of a connection to the data store.
• Improves performance by caching information used by ICA Clients for enumeration and application resolution.

The LHC is an Access database, Imalhc.mdb, stored, by default, in the \Citrix\Independent Management Architecture folder.

The following information is contained in the local host cache:

• All servers in the farm, and their basic information.
• All applications published within the farm and their properties.
• All Windows network domain trust relationships within the farm.
• All information specific to itself. (Product code, SNMP settings, licensing information)

On the first startup of the member server, the LHC is populated with a subset of information from the data store. In future, the IMA service is responsible for keeping the LHC synchronized with the data store. The IMA service performs this task through change notifications and periodic polling of the data store.

If the data store is unreachable, the LHC contains enough information about the farm to allow normal operations for an indefinite period of time, if necessary. However, no new static information can be published, or added to the farm, until the farm data store is reachable and operational again.

Note: Before the release of Presentation Server 3.0, the LHC had a grace period of only 96 hours; this was due to farm licensing information being kept on the data store. Once the 96 hour grace period ended, the licensing subsystem would fail to verify licensing, and the server would stop accepting incoming connections.

Because the LHC holds a copy of the published applications and Windows domain trust relationships, ICA Client application enumeration requests can be resolved locally by the LHC. This provides a faster response to the ICA Client for application enumerations as the local server does not have to contact other member servers or the zone data collector. The member server must still contact the zone data collector for load management resolutions.

In some instances it might be necessary to either refresh or recreate the Local Host Cache. The sections below describe these situations.

Refreshing the Local Host Cache

If the IMA service is currently running, but published applications do not appear correctly in ICA Client application browsing, force a manual refresh of the local host cache by executing dsmaint refreshlhc from a command prompt on the affected server. This action forces the local host cache to read all changes immediately from the data store.

A discrepancy in the local host cache occurs only if the IMA service on a server misses a change event and is not synchronized correctly with the data store.

Recreating the Local Host Cache

• If the IMA service does not start, the cause may be a corrupt LHC.
• If you have made extensive changes to the farm data store, such as publishing various applications, adding or removing servers from the farm, or creating new policies.
• If you must clean the farm data store, using the DSCHECK utility, you should then rebuild the LHC on each of the servers in your farm, once the data store has been cleaned.

Steps to recreate the Local Host Cache

IMPORTANT: The data store server must be available for dsmaint recreatelhc to work. If the data store is not available, the IMA service cannot start.

1. Stop the IMA service on the XenApp server, if it is started. This can be done using the command: net stop imaservice, or from services.

2. Run dsmaint recreatelhc, which renames the existing LHC database, creates a new database, and modifies the following registry key HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\IMA\Runtime\PSRequired key to 1.
   Setting the value PSRequired to 1 forces the server to establish communication with the data store in order to populate the Local Host Cache database. When the IMA service is restarted, the LHC is recreated with the current data from the data store.

3. Restart the IMA service. This can be done via the command line, net start imaservice, or from services.

Note: For XenApp 6 or later the registry key path is HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Citrix\IMA\ RUNTIME\PSRequired to 1.

There is also an available built-in utility to check the Local Host Cache called LHCTestACLsUtil.exe file located in C:\Program Files (x86)\Citrix\System32 of the XenApp server. To run this utility, you must have local administrator privileges.

2.      Citrix load evaluators

XenApp calculates the load on a server using load evaluators and rules. Each load evaluator contains one or more rules. Each rule defines an operational range for the server or published application to which its evaluator is assigned.

There are three types:

1.Default loader: it considers how any number of users log on to the server.(user count 100%).

2. Advanced loader: It considers depends on cpu and memory utilization up to 100%

3. Custom load evaluators

3.      What is the name of the product citrix uses for licensing?

http://support.citrix.com/article/CTX113429

Citrix products use the FLEXlm licensing technology for licensing.  

4.      Why is ica that much faster than rdp? What are the technological differences between the two?

ICA- Independent Computing Architecture (Citrix Protocol) 1494
RDP- Remote Desktop Protocol (Microsoft protocol) 3389

The Difference between Microsoft RDP and Citrix ICA
Windows 2000/2003 Terminal Services supports the native Microsoft Remote Desktop Protocol (RDP) as well as the Citrix Independent Computing Architecture (ICA) protocol (via the Citrix MetaFrame add-on). The following table provides an overview of the features available with each of these protocols:

Table: Windows 2000/2003 Terminal Services supported protocols and features:

Feature	Description	RDP	ICA
Clients	Windows CE-based thin client	+	+
	Windows XP Embedded-based thin client	+	+
	ActiveX® Control	+	+
Transport	TCP/IP	+	+
	SPX, IPX, NetBEUI		+
	WAN connection	+	+
	Dial-up, VPN, xDSL	+	+
	Direct dial-up (non-RAS)		+
Audio	System beeps	+	+
	Stereo Windows audio		+
Local printing	Printing to a local printer attached to a thin client	+	+
Local drive mapping	Local drives accessible from server-based applications	+	+
Local port redirection	Redirection of server ports (LPT/COM) to local client ports	+	+
Cut and paste	Cut and paste of text and graphics between client and server	+	+
User-centric Session Access	Client remembers previous user's logon name for each connection	+
	Connect to an active or disconnected session using a different screen resolution	+
	Connect directly to an application rather than to an entire desktop	+	+
	Server-based applications resize and minimize similar to local applications		+
Application publishing	Advertise server-based applications directly to client desktops		+
Resolution	16-bit color depth	+	+
Load balancing	Pooling of servers behind a single server address and for increased availability	+ 1	+
Remote control	Viewing and interacting with other client sessions (also called "shadowing")	+	+
Bitmap caching	Optionally cache display bitmaps in memory for improved performance	+	+
	Optionally cache display bitmaps to disk for improved performance	+	+
Encryption	Multiple-level encryption for security of client communications	+	+
	Multiple-level encryption on Windows CE thin clients	+
Automatic client update	Administrative means for updating client connection software from the server	+ 2	+
Pre-configured client	Predefined client with published applications, IP addresses, server names, and connection options	+	+

1 Requires Windows 2000 Advanced Server or Datacenter Server.
2 Not available on Windows CE .NET thin clients.

Default ICA port ?
A: 1494
NOTE: Default ICA port is a common question to ask in the interview: Apart from this, should be ready with all Port details which are related to the citrix environment.
Port Name Port Number
Default listening port for Citrix XML Service : 80
CMC, SSL : 443
Server to SQL : 1433
ICA : 1494
UDP port used for client broadcast : 1604
IMA : 2512, 2513
Session Reliability : 2598
Licensing : 27000
Citrix License Administration Console : 8082