11.6 Imaging Considerations

Imaging devices can have a significant impact on the network, both from the sheer amount of data that is transmitted and from a configuration perspective. The amount of network traffic will be based on the size of the image being deployed and the number of images being deployed. On sites separated from the Primary Server by a slow or saturated link, it is important that you place a local imaging Satellite to ensure successful performance imaging. From a network configuration issue perspective there are two important considerations:

11.6.1 Supporting ZENworks Preboot Services

If you want to allow managed devices to be automatically imaged over the network via ZENworks imaging and PXE, you might need to make the following changes to your network:

  • Ensure that there is a ZENworks Imaging server with Proxy DHCP enabled on the subnet as the managed device, or configure a secondary IP Helper on the router or switch such that it routes DHCP requests not only to your DHCP server, but also to a ZENworks Imaging server.

  • If you are installing the ZENworks Imaging server with Proxy DHCP on the same machine as your DHCP server, you will need to properly configure the Proxy DHCP server to listen for requests on the alternate DHCP port (4011) and configure the novell-proxydhcp.conf file to indicate that there is a local DHCP server.

  • The spanning tree protocol (STP) is available on certain switches and is designed to detect loops in the network. When a device (typically a network hub or a device) is patched into a port on the switch, the switch indicates to the device that the link is active. However, instead of forwarding frames from the port to the rest of the network, the switch checks each frame for loops and then drops it. The switch can remain in this listening state from 15 to 45 seconds.

    The effect of this is to cause the DHCP requests issued by PXE to be dropped by the switch, causing the Preboot Services session to fail.

    It is normally possible to see that the STP is in progress by looking at the link light on the switch. When the device is off, the link light on the switch is obviously off. When the device is turned on, the link light changes to amber. After a period of time it changes to a normal green indicator. As long as the link light is amber, STP is in progress.

    This problem only affects PXE devices that are patched directly into an Ethernet switch. To correct this problem, do one of the following:

    • Turn off STP on the switch entirely.

    • Set STP to Port Fast for every port on the network switch where a PXE device is attached.

    After the problem is resolved, the link light on the port should change to green almost immediately after a device connected to that port is turned on.

11.6.2 Supporting Multicast Imaging

If you plan to use multicast to image a large number of machines simultaneously with the same image, you might need to make the following changes:

  • Ensure that any switch or router between the Primary Server and the devices being imaged is configured to forward multicast packets.

  • Ensure that any switch or router between the Primary Server is configured to use IGMP so that multicast packets are only forwarded to those devices that register with the multicast group being used for a given multicast session.