High Availability for TFTP with Provisioning Services

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Worldwide Consulting Solutions | WHITE PAPER | Implementation Guide

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High Availability for TFTP with

Provisioning Services

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Contents

Overview ... 3

Options ... 4

DNS Round Robin Entry... 5

DHCP with Multiple Entries ... 5

Provisioning Services PXE Broadcast ... 5

Provisioning Services Boot Device Manager ... 6

NetScaler Use Source IP... 6

NetScaler Direct Server Return ... 7

NetScaler Global Server Load Balancing ... 7

Summary ... 8

Implementation Guide ... 9

Prerequisites ... 10

NetScaler General Configuration ... 14

NetScaler – Use Source IP ... 17

NetScaler – Direct Server Return ... 22

NetScaler – Global Server Load Balancing ... 28

Appendix A – Environment Details ... 35

Appendix B – Reference Documentation ... 35

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Overview

Citrix Provisioning Services is a software streaming technology that allows servers and desktops to be provisioned and re-provisioned in real time from a single shared-disk image1_{. The service is}

commonly integrated with Citrix virtualization solutions to optimize Operating System delivery and management.

Often these solutions are critical to the operation of organizations and require high availability. Providing high availability for Provisioning Services requires designing each component of the service without a single point of failure across the network. The „bootstrap file‟, named

ardbp32.bin, is a key component that must be delivered to Provisioning Services target devices in order for them to communicate with Provisioning Services over the network.

The bootstrap file is typically delivered via Trivial File Transfer Protocol (TFTP) services hosted on Provisioning Servers. This document focuses specifically on comparing high availability options for delivery of the bootstrap file to target devices via TFTP. The advantages and disadvantages of each option are outlined as well as the steps to implement the load balancing options with NetScaler. The document scope does not include details of the implementation or operation of other aspects of Provisioning Services.

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Options

The options under consideration share common components including:

 Dynamic Host Configuration Protocol (DHCP)2_:_{Provides hosts with networking} information they need to communicate on the network. It provides a host with an IP address, gateway, and DNS server(s) by default. Two additional “options” carry additional information that are used by Provisioning Services target devices to obtain their bootstrap file.

o Option 66: Defines the Boot Server Host Name, which corresponds to the TFTP

Server DNS name or IP address

o Option 67: Defines the Bootfile Name, which is typically ardbp32.bin

 Pre-boot Execution Environment (PXE)3_:_{Is a program included in computer firmware} that enables it to boot over the network. It relies on DHCP to obtain information necessary to boot. When a computer first attempts a PXE boot it broadcasts a DHCP request over its Network Interface Card (NIC)/(s).

 Trivial File Transfer Protocol (TFTP)4_:_{Provides PXE clients with their bootstrap file.} Clients are typically notified of the TFTP Server/(s) and the bootstrap file name through DHCP options. The lab environment used to implement the options has a TFTP service running on each Provisioning Services server, so they will be referenced as Provisioning Services/TFTP Servers.

 Domain Name System (DNS)5_:_{Allows common names to be mapped to and from IP}

addresses. By providing dynamic allocation of its directory information Provisioning Services target devices may be presented with different Provisioning Services/TFTP Server IP addresses providing a rudimentary level of redundancy.

The core concept with regards to providing high availability to TFTP is being able to deliver the bootstrap file to the Provisioning Services target device. Once the bootstrap is delivered, the target device can communicate to multiple Provisioning Services servers. There are many different ways for providing high availability for the TFTP services, but the following seven are the most common:

1. DNS Round Robin Entry

2. DHCP with Multiple Entries

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4. Provisioning Services Boot Device Manager

5. NetScaler Use Source IP (USIP)

6. NetScaler Direct Server Return (DSR)

7. NetScaler Global Server Load Balancing (GSLB)

DNS Round Robin Entry

With this option, a TFTP server DNS name is carried in DHCP option 66. The DNS server then would have two or more A records defined for the domain name and cycle through the list of records in round robin fashion in response to DNS queries. This provides Provisioning Services target devices with redundancy in obtaining their Bootfile.

 Advantages of this option:

o It is easy to implement requiring limited changes to DHCP and DNS servers.

 Disadvantages of this option:

o It may not monitor the state of target TFTP servers, depending on the DNS

server; therefore it could potentially send requests to servers that are not functioning.

DHCP with Multiple Entries

This option requires a DHCP implementation that allows multiple Boot Server Host Name entries to be carried within the option 66 field.

o It is easy to implement requiring limited changes to DHCP servers only.

o It does not monitor the state of target TFTP servers; therefore it could send

requests to servers that are not functioning.

Provisioning Services PXE Broadcast

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Without the helper address, the requests would otherwise be contained within the subnet and unable to reach the PXE service.

o It is easy to implement, requiring limited changes to routers only.

o IP/UDP helper address entries are typically already configured within networks

to deliver client DHCP requests to DHCP server farms.

o It increases traffic on the network and can present risks to its capacity in the event of a malfunctioning PXE client, or virus that sends excessive broadcasts.

Provisioning Services Boot Device Manager

This Provisioning Services option is different than the other options in that it does not rely on the client PXE booting itself from a TFTP Server. Rather, the Boot Device Manager creates a Bootfile that the target device can obtain via an ISO image mounted to the virtual machine as a DVD drive. For this to be a high-availability option for delivery of the Bootfile, the network share containing the ISO file must be redundant.

o It has limited reliance on the network infrastructure.

o It requires changes to the target device boot process (boot via DVD instead of

network).

o Updating the ISO file is a manual process, which is why the addresses used within

the file should be a fully qualified domain name, whose IP address can be updated in DNS later.

NetScaler Use Source IP

This option relies on the NetScaler to load balance the target device‟s initial TFTP boot request to a TFTP Server. The target devices must obtain the IP address of the NetScaler Virtual Server IP (VIP) through DHCP option 66. Once the NetScaler receives the boot request, it is directed to one of the TFTP servers from the pool by changing the destination IP address. The source IP address is not changed, therefore the TFTP server replies to the target device directly.

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o None

NetScaler Direct Server Return

This option is similar to the NetScaler – Use Source IP option, but it makes its load balancing decision based on the frame MAC Address and does not change the target destination IP address. Therefore the target TFTP Server must have a loopback IP address corresponding to the NetScaler VIP.

o Provides robust scalability and availability as with the NetScaler-Use Source IP

option.

o Requires configuring a loopback address on the TFTP Servers

NetScaler Global Server Load Balancing

This option takes advantage of the NetScaler ability to integrate with DNS to control responses to queries while monitoring the availability of TFTP servers. Upon receiving a DNS query for the TFTP boot server domain name, the NetScaler dynamically responds with the best option, according to the selection algorithm configured.

o Provides availability monitoring of Provisioning Services/TFTP Servers

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Summary

Based on all of the options, the following provides a quick summary for how difficult they are to implement, how scalable they are and how fault tolerant they are (ability to identify issues and reroute requests appropriately).

Option Difficulty Scalability Fault Tolerance

DNS Round Robin Entry Low Medium Low DHCP with Multiple Entries Low Low Low Provisioning Services PXE Broadcast Low Medium Medium Provisioning Services Boot Manager Medium Medium High NetScaler Use Source IP Low High High NetScaler Direct Server Return Medium High High NetScaler Global Server Load Balancing High High High

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Implementation Guide

Of the previously mentioned high availability options for TFTP, the three NetScaler options require additional help in the setup/configuration. This section of the document focuses on the

implementation of the NetScaler options.

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Prerequisites

Below is a complete list of components required to implement the NetScaler based options within a lab environment.

Prerequisites

The following components must be installed to complete the implementation scenarios contained in this section

 Install a XenServer capable of hosting all required Virtual Machines (VMs)  Install 2 Provisioning Services VMs including:

o The TFTP Server component configured

o A license server & license

o A Provisioning Services Bootstrap with pertinent configuration  Install a Domain Controller(DC) VM including:

o A DHCP service with pertinent options set

o A DNS service with pertinent A records configured  Install a Vyatta Router VM with pertinent settings configured

 Install a NetScaler VM with pertinent settings configured & license applied  Install 2 Provisioning Services Clients

o One on the XenServer internal network Provisioning Services – TFTP

o Another on the XenServer internal network Provisioning Services – TFTP2

Screenshot Description

Install a XenServer

 XenServer version 5.6_SP2 running on an HP Proliant 380 with 16MB RAM and an internal HD was used for this setup

 The XenServer hosts 6 VMs described in the following blocks and 3 Networks described below

 Provisioning Services – TFTP is an internal network that corresponds to subnet 192.168.0.0/24

 Provisioning Services – TFTP2 is an internal network that corresponds to subnet 10.95.95.0/24

 Network 1 corresponds to an external network used for management access only that corresponds to subnet 172.17.2.0/24

See Appendix B - Reference Documentation for more information regarding installation

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Prerequisites

Install a NetScaler VM

 NetScaler version 9.3_51_nc

 Add an interface to network Provisioning Services - TFTP

NOTE: The NetScaler should be configured in a High Availability pair

Install a Vyatta Router VM

 Vyatta Version 2.6.35-1

 Add an interface to network Provisioning Services - TFTP

 Add an interface to network Provisioning Services – TFTP2

Install a Domain Controller with DHCP and DNS Roles

 Add an interface to Provisioning Services – TFTP

 Add an interface to Provisioning Services – TFTP2

 Add an interface to Network 1 See Appendix B - Reference Documentation for more information regarding installation

Configure Domain Controller

 Create Domain “pvslab.com”

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Prerequisites

Configure DHCP Server

 Open the Windows Server Manager

 Select the DHCP Server Role

 Configure Scope 192.168.0.0 corresponding to network Provisioning Services – TFTP1 with Address Pool 192.168.0.50-192.168.0.59

 Configure Scope 10.95.95.0

corresponding to network Provisioning Services – TFTP2 with Address Pool 10.95.95.50-10.95.95.59

Install Provisioning Services Client VMs

 Provisioning Services Client1 is a XenServer VM with an interface on an internal network Provisioning Services – TFTP

 Provisioning Services Client2 is a XenServer VM with an interface on an internal network Provisioning Services – TFTP2

Set Provisioning Services client Boot Option:

 Select the Provisioning Services Client 1 VM

o Select General Tab

o Select Properties

o Select Boot Options

o Specify: Network and ensure other options are unchecked

 Repeat for the Provisioning Services Client 2 VM

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Prerequisites

Install Provisioning Services/TFTP Server VMs

For both Provisioning Services/TFTP Server 1 & 2:

 Add an interface to Provisioning Services – TFTP

 Add an interface to Network 1

 Install Provisioning Services Version 5.6.2 including:

o TFTP Server Provisioning Services Bootstrap with pertinent configuration See Appendix B - Reference Documentation for more information regarding installation

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NetScaler General Configuration

Base Configuration

Configure the NetScaler with a NetScaler IP (NSIP) address and a default gateway.

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Download your license and the latest NetScaler firmware from www.mycitrix.com.

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Connect to the NetScaler

 Enter the NetScaler‟s IP Address (NSIP) in the web browser: http://192.168.0.95  Log into the Configuration system with the

ID and Password NOTE: The default credentials are: Username = nsroot

Password = nsroot

Apply license file

Under:

>System>License>Manage Licenses>Add

 Upload your license file to the NetScaler using the License utility

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Upgrade the NetScaler

Under:

>NetScaler>Upgrade Wizard

 Follow the wizard prompts. Enter „Yes‟ when prompted whether to reboot.

 Re-connect to the NetScaler after it has rebooted

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Enable Load Balancing

Under:

>System>Settings>Configure Basic Features Select:

 Enable Load Balancing

Add Provisioning Services/TFTP Servers

Under:

>Load Balancing>Servers

In order to load balance TFTP services, the servers hosting the service must first be defined by doing the following:

 Select Add from the bottom menu bar

 In the Create Server window, enter in the following information for the first Provisioning Services/TFTP Server:

o Server Name: pvs-server1

o IP Address: 192.168.0.98

o Select Create

 For the second Provisioning Services/TFTP Server, enter in the following:

o IP Address: 192.168.0.99

o Select Create

 Select Close

 Each Server entry should appear “green”. If not check reachability from the

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NetScaler – Use Source IP

The network topology pertaining to implementation of this option is shown in the following figure:

With this option, each of the Provisioning Services Client VMs are restarted and follow the respective paths, outlined above, sequentially to obtain their bootfile.

 Provisioning Services Client 1

o Broadcasts a DHCP request, which is replied to by the DHCP Server carrying its

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o Provisioning Services/TFTP Server 1 receives the boot request with the source IP address of Provisioning Services Client 1 and sends it the initial segment of its bootfile

o Broadcasts a DHCP request which is replied to by the DHCP Server carrying its

IP address, Gateway, Boot Server Host Name, and Bootfile Name.

o Sends a TFTP boot request to the NetScaler VIP via its gateway, the Vyatta

router.

o The NetScaler makes a load balancing decision and subsequently in this case

changes the destination IP address to that of Provisioning Services/TFTP Server 2 where it directs the boot request.

o Provisioning Services/TFTP Server 2 receives the boot request with the source

IP address of Provisioning Services Client 2 and sends it the initial segment of its bootfile.

Configuration

Configure a Subnet IP (SNIP)

Under: >Network>IPs>

 In the Configure IP window enter the following:

o IP Address: 192.168.0.94

o Select: OK

This will be used as the source IP address for monitoring the Provisioning Services/TFTP Servers.

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Configuration

Add Provisioning Services Service Group

Under:

>Load Balancing>Service Groups

 In the Create Service Group window enter the following:

o Service Group Name: Provisioning Services Service Group

o Protocol: ANY

o Select: pvs-server1 (192.168.0.99)

 Select the Members tab:

o Select Server Based

o Highlight pvs-server1 o Port: * o Select Add o Highlight pvs-server2 o Port: * o Select Add

 Select the Advanced tab:

o Select:: Use Source IP

o Select Create

o Select Close

NOTE: The service group monitor was left as ping-default

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Configuration

Add Provisioning Services Virtual Server

Under:

>Load Balancing>Services

 In the Create Virtual Server window, enter the following information:

o Name: tftp-any

o IP Address: 192.168.0.90

o Protocol: ANY

o Port: *

 Select the Service Groups tab:

o Select: Provisioning Services Service Group

 Select the Method & Persistence tab:

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Configuration

Configure DHCP Options

 Configure Scope 192.168.0.0 corresponding to network Provisioning Services – TFTP2 with Scope Options:

o 066 Boot Server Host Name = 192.168.0.90

o 067 Bootfile Name = ARDBP32.bin

o 066 Boot Server Host Name = 192.168.0.90

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NetScaler – Direct Server Return

With this option each of the Provisioning Services Client VMs are restarted and follow the respective paths, outlined above, sequentially to obtain their bootfile.

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destination MAC address is modified. The frame arrives at Provisioning Services/TFTP Server 1 with the same destination IP address as the NetScaler VIP.

o Provisioning Services/TFTP Server 1 receives the boot request on its external

interface and forwards it to its loopback adapter with the same IP address as the NetScaler VIP. It then sends to the source IP address, which is Provisioning Services Client 1, the initial segment of its bootfile.

o Sends a TFTP boot request to the NetScaler VIP via its gateway, the Vyatta

router.

o The NetScaler makes a load balancing decision and directs the boot request to

Provisioning Services/TFTP Server 2. However in this case it does not change the IP destination to Provisioning Services/TFTP Server 2, rather only the destination mac address is modified. The frame arrives at Provisioning

Services/TFTP Server 2 with the same destination IP address as the NetScaler VIP.

o Provisioning Services/TFTP Server 2 receives the boot request on its external

interface and forwards it to its loopback adapter with the same IP address as the NetScaler VIP. It then sends to the source IP address, which is Provisioning Services Client 2, the initial segment of its bootfile.

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Configuration of the DSR method is similar to the configuration for USIP, yet requires the following changes to the NetScaler configuration:

MAC Based Redirection Mode

Under:

>System>Load Balancing>Virtual Servers>

 Highlight the „tftp-any‟ Virtual Server

 Select: Open

 Select: Advanced TAB

 Select: MAC Based next to Redirection Mode

 Select: Ok

Configuration of the DSR method also requires configuring a loopback on each Provisioning Services/TFTP Server with an IP address which corresponds to the NetScaler VIP and setting the TFTP service to listen on that loopback. Instructions are included for MS Windows Servers only:

Add MS Loopback adaptor to TFTP servers

 From the Windows Start button:

o Right-click: Computer

o Select: Properties

o Select: Device Manager

o Right-click: <Computer Name>

o Select: Add Legacy Hardware

o Click: Next

o Select: Install the hardware I manually select from a list

o Click: Next

o Select: Network Adapters

o Click: Next

o Select: Microsoft

o Select: Microsoft Loopback Adapter

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Add VIP IP address to MS Loopback adaptor

 From the Windows Start button:

o Select: Control Panel

o Select: Network and Internet

o Select: Network and Sharing Center

o Select: Local Area Connection 3 (The loopback being the last added will be the highest number)

o Select: Internet Protocol Version 4

o Select: Use the following IP address o Enter:  IP Address: 192.168.0.90  Subnet mask:255.255.255.0

o Click: Ok & Close all other windows

NOTE: It is not necessary to specify a default gateway. This should already be specified on the primary interface as the Vyatta router.

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Configure adapters to send and receive for loopback

This step is necessary in order to allow the server interfaces to send and receive traffic destine for the IP addresses of both the loopback and external

interfaces

 From the Windows Command prompt enter:

o netsh

o interface

o ipv4

o set interface "Local Area Connection"

weakhostreceive=enabled

o set interface "Local Area Connection 3"

weakhostreceive=enabled

o set interface "Local Area Connection 3"

weakhostsend=enabled For more information see this article on Microsoft TechNet:

http://technet.microsoft.com/en-us/magazine/2007.09.cableguy.aspx

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Bind TFTP Service to Loopback

This step is necessary in order to allow the

Provisioning Services/TFTP Servers to receive TFTP requests on the loopback interface.

 Open Windows Explorer:

o Browse to C:\Program

Files\Citrix\Provisioning Services

o Double click tftpcpl.cpl

o Select the TFTP Network TAB

o Select the loopback 192.168.0.90

o Click OK

o Click Yes to restart the TFTP service

 To verify open a DOS prompt and enter:

o Netstat –na | findstr 192.168.0.90:69

o The output should reflect the loopback listening on UDP port 69

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NetScaler – Global Server Load Balancing

With this option each of the Provisioning Services Client VMs are restarted and follow the respective paths, outlined above, sequentially to obtain their bootfile.

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process dynamically and based on the least connected algorithm returns the Provisioning Services/TFTP Server 1 in the DNS reply.

o The DNS Server sends this DNS reply to Provisioning Services Client 1

o Sends a TFTP boot request to the Provisioning Services/TFTP Server 1 and it

initiates TFTP transfer of the bootfile to the Provisioning Services Client 1.

o Attempts to resolve the Boot Server Host Name „tftp‟ from the DNS Server.

o The DNS Server is configured with an alias for „tftp‟ that references the NetScaler

Authoritative DNS (ADNS) listener. A DNS name query is forwarded to NetScaler2, from the DNS server, on behalf of Provisioning Services Client 2. Once the NetScaler2 ADNS process receives the request it queries the GSLB process dynamically and based on the least connected algorithm returns the Provisioning Services/TFTP Server 2 in the DNS reply.

o The DNS Server sends this DNS reply to Provisioning Services Client 2

o Sends a TFTP boot request to the Provisioning Services/TFTP Server 2 and it

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The NetScaler - GSLB method is configured as follows: Configuration

Enable GSLB Service

Under:

>System>Settings>Configure Advanced Features

Configure the ADNS Service

Under:

>Load Balancing> Services>

 In the Configure IP window enter the following:

o Service Name: ADNS

o Protocol: ADNS o Server: 192.168.0.94 o Port: 53  Select Create  Select Close Add GSLB Site Under: >GSLB>Sites

Site1 – “Provisioning Services – TFTP”

o Select Add from the bottom menu bar

o In the Create GSLB site window enter the following:

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Configuration

Add GSLB Services

Under:

>GSLB>Services

Provisioning Services – TFTP – SERVER1

 In the Create GSLB Service window enter the following:

o Service Name: Provisioning Services – TFTP – SERVER1

o Service Type: UDP

o Port: 69

 Select Create

Provisioning Services – TFTP – SERVER2

 Again In the Create GSLB Service window enter the following:

o Service Name: Provisioning Services – TFTP – SERVER2

o Service Type: UDP

o Port: 69

 Select Create

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Configuration

Add GSLB Virtual Server

Under:

>GSLB>Virtual Servers

 Select Add from the bottom menu bar In the Create GSLB Virtual Server window

 Under the Services Tab:

o Select: Provisioning Services – TFTP – SERVER1

o Select: Provisioning Services – TFTP – SERVER2

NOTE: The “Effective State” will show DOWN the state of the services is not being communicated via MEP since a remote site is not being used.

 Under the Domain Tab:

o Select Add

o Enter Domain Name: tftp.gslb.pvslab.com

 Select Create

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Configuration

Update DHCP Options

o 066 Boot Server Host Name = tftp.pvslab.com

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With the TFTP – GSLB option the DNS server must be configured with a Name Server for the NetScaler ADNS service, a „gslb‟ subdomain, and an alias directing queries for the „tftp‟ name to it.

Configuration

Configure DNS Server

 Select the DNS Server Role

 Right-click on the pvslab.com domain entry and select "New Delegation"

o Click: Next

o Enter: gslb

o Click: Next

 Select Add Name Server

o Name: ns1

o Select: <Click here to add an IP Address>

o IP: 192.168.0.94

o Click: OK

o Click: Next

o Click: Finish

 Right-click on the pvslab.com domain entry and select "New Alias (CNAME)"

o Alias Name: tftp

o FQDN: tftp.gslb.pvslab.com

o Click: Ok

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Appendix A – Environment Details

Component Details

Provisioning Services Version 5.6.2

XenServer Version 5.6_2

NetScaler VPX Version 9.3-51.5 Windows Server Version 2008 R2 Vyatta Router Version 2.6.35-1

Appendix B – Reference Documentation

How to Add DHCP PXE Options to Microsoft DHCP Server

http://support.citrix.com/article/CTX115094

Requirements for Internet Hosts -- Communication Layers

http://datatracker.ietf.org/doc/rfc1122/?include_text=1

The Cable Guy: Strong and Weak Host Models

http://technet.microsoft.com/en-us/magazine/2007.09.cableguy.aspx

Provisioning Server High Availability Considerations

http://support.citrix.com/servlet/KbServlet/download/18737-102-445549/Provisioning_Server_High_Availability_Considerations2.pdf

Installing Windows Server 2008 DHCP Server

http://www.windowsnetworking.com/articles_tutorials/How-to-Install-Configure-Windows-Server-2008-DHCP-Server.html

How to Add DHCP PXE Options to Microsoft DHCP Server

Using Provisioning Services Boot Device Manger with XenDesktop and XenServer

http://blogs.citrix.com/2009/02/25/using-pvs-boot-device-manger-with-XenDesktop-and-XenServer/

Using the Manage Boot Devices Utility

http://support.citrix.com/proddocs/topic/provisioning-56/pvs-boot-devices-utility.html

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http://docs.vmd.citrix.com/XenServer/5.6.0fp1/1.0/en_gb/QuickStartGuide_Basi cVersion.html

Citrix NetScaler VPX Getting Started Guide - Release 9.3

Provisioning Server and Citrix License Server Interaction FAQ

Redundancy and Scalability for TFTP using NetScaler Direct Server Return

http://blogs.citrix.com/2010/11/11/redundancy-and-scalability-for-tftp-using-NetScaler-direct-server-return/

Configuring Load Balancing in Direct Server Return Mode

http://support.citrix.com/proddocs/topic/NetScaler-load-balancing-93/ns-lb-usecases-dsrmode-con.html#ns-lb-usecases-dsrmode-con

Load Balancing TFTP – Anything But Trivial

http://blogs.citrix.com/2011/05/02/load-balancing-tftp-anything-but-trivial/

Citrix NetScaler Networking Guide

http://support.citrix.com/servlet/KbServlet/download/27520-102-659875/NetScaler-Networking-Guide.pdf

Using a NetScaler Appliance in the Use Source IP Mode

Does Use Source IP Mode Work in a NetScaler One-arm Mode Deployment?

FAQ: The USIP Address Mode of the NetScaler Appliance

How to Load Balance Trivial File Transfer Protocol Servers

How to Configure the Direct Server Return on a NetScaler Appliance

High Availability for Desktop Virtualization

http://support.citrix.com/servlet/KbServlet/download/21773-102-650177/XD%20-%20High%20Availability%20-%20Implementation%20Guide.pdf

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Revision History

Revision Change Description Updated By Date

1.0 Document complete Matt Brooks – Principal Consultant

Nicholas Rintalan – Sr. Architect December 1, 2011

About Citrix

Citrix Systems, Inc. (NASDAQ:CTXS) is the leading provider of virtualization, networking and software as a service technologies for more than 230,000 organizations worldwide. It’s Citrix Delivery Center, Citrix Cloud Center (C3) and Citrix Online Services product families radically simplify computing for millions of users, delivering applications as an on-demand service to any user, in any location on any device. Citrix customers include the world’s largest Internet companies, 99 percent of Fortune Global 500 enterprises, and hundreds of thousands of small businesses and prosumers worldwide. Citrix partners with over 10,000 companies worldwide in more than 100 countries. Founded in 1989, annual revenue in 2010 was $1.9 billion.

©2011 Citrix Systems, Inc. All rights reserved. Citrix®, Access Gateway™, Branch Repeater™, Citrix Repeater™, HDX™, XenServer™, XenApp™, XenDesktop™ and Citrix Delivery Center™ are trademarks of Citrix Systems, Inc. and/or one or more of its subsidiaries, and may be registered in the United States Patent and Trademark Office and in other countries. All other trademarks and registered trademarks are property of their respective owners.