Designing a PXE Network

A number of considerations and rules need to be observed when implementing the Preboot Execution Environment (PXE) in a network. Your implementation of the PXE system will be affected by the number of ZfD 3.2 Preboot Services PXE clients that are to be supported as well as the network bandwidth that is available. The use of network bandwidth across wide area network (WAN) links requires special consideration. You will also have to make configuration changes to the PXE system if the network spans multiple subnets.

This section contains information on the following topics:

• Understanding the Client to Server Component
• Network Design Considerations

Understanding the Client to Server Component

Design your Client to Server component so that Preboot Services clients can effectively connect to the Transaction Server as well as to the TFTP or MTFTP Servers. The important points here include the number of Preboot Services clients to be installed on the network and the bandwidth available to service these clients.

When a ZfD 3.2 Preboot Services client or a PXE client executes on a workstation, it will typically perform six steps:

1. Broadcast a request for a DHCP Server to provide the client with an IP address. Either a Preboot Services client or a PXE client executing on the workstation will perform this step. In the case of a PXE client this step is used to get the information necessary to download the Preboot Services client.

   The standard DHCP Server will respond to provide the client with the necessary IP address. The Preboot Services Proxy DHCP Server will also respond to the client to provide the client with two IP addresses: an address for the Transaction Server and an address for the TFTP and MTFTP servers.

   NOTE:  The Preboot Services Proxy DHCP does not provide an IP address to the Preboot Services client, it only supplies the client with the IP addresses of the servers that the client needs to connect to for a successful PXE session.

2. If the client that executed in Step 1 was a PXE client, then the PXE client will download the Preboot Services client from the MTFTP Server. The address of the MTFTP Server was obtained in Step 1 from the Preboot Services Proxy DHCP Server. This step will require the client to download a single file of less than 64 kilobytes. In the case where the Preboot Services client was already executing (for example, Preboot Services Boot Diskette or Preboot Services Boot Sector) this step will not occur.
3. If a Preboot Services client was downloaded in Step 2, then it will perform a network broadcast to request IP address information. The standard DHCP Server and Preboot Services Proxy DHCP Server will respond again with the same information that they provided in Step 1. It is not important for the standard DHCP Server to provide the same client IP address in Steps 1 and 3.
4. The Preboot Services client connects to the Preboot Services Transaction Server and authenticates with the server. The Transaction Server will determine if any actions should execute on the client and return the necessary information to the client. If the Transaction Server does not have any actions for the client to execute, the client will shut down and the client workstation will continue to execute normally.
5. If an action was given to the Preboot Services client, the client will connect to the TFTP Server to download the specified action file. The size of the download file can vary a great deal depending on the action to be performed and can range from a few kilobytes for an action such as hardware inventory, to over a megabyte for a complex action such as system healing.

Once the action has been completed, the Preboot Services client will go to Step 4 to determine if there are any more actions outstanding.

Network Design Considerations

Use the following guidelines as you consider how to design your network for Preboot Services:

• Only one Proxy DHCP Server should be installed per DHCP Server scope
• Only one Proxy DHCP Server should exist on a subnet
• It is typical to have only one Proxy DHCP Server on the network

TFTP Servers should be installed so that Preboot Services clients have access to a TFTP Server within their LAN. The bulk of network traffic generated by Preboot Services is between the Preboot Services clients and the TFTP Server. A good design will ensure that a client will not need to connect to its TFTP Server through a slow WAN link.