Monday, August 07, 2006

PXE wireless booting


Introduction


From time to time, in the thin client, network booting, LTSP (Linux Terminal Server Project) and other related technologies mailing lists the same question arise: how do I boot off the network with a wireless card ?

Sometimes, the answer derives to the use of flash disk or other local boot methods,but strictly speaking this is not a wireless booting and the thin client is not thin anymore.

The approach presented here doesn't require the use of a hard disk, flash memory or other local storage device. The nature of the network boot is preserved.

Although, you need to add an additional piece of hardware which is a wireless bridge.

There's a subtle difference between access points and wireless bridges which sometimes is not clear enough. Thus, our first step will be to depict this difference.

Access points


Access points are the most common element in wireless networks.

The 802.11 standard defines an access point as a communication hub for users of a wireless device to connect to a wired distribution system, such as an Ethernet network. Access points also play a major role in providing access control and wireless security to users in the shared radio environment.

Wireless bridges


Unless the 802.11 standard doesn't specifically define a bridge some vendors offer wireless briges as a simplified and somewhat different from access points.

A bridge is a device that connects two networks that may use the same or a different Data Link Layer protocol (Layer 2 of the OSI Model). Bridges have been in use for decades, especially with wired networks.

Access points connect multiple users on a wireless LAN to each other and to a wired network while a bridge connects two different networks.

The simplest case is a basic Ethernet-to-wireless bridge. This type connects directly to a single device via an Ethernet port, and then provides a wireless connection to an access point.

These types of device provides the solution when the device (i.e: thin client) has an Ethernet port but no 802.11 NIC.




Available Ethernet-to-wireless bridges
  • D-Link model number DWL-7700AP
  • Linksys model number WET54G
  • Cisco Aironet 1300 Series




Wireless network booting


Because, as far as I know, there's no wireless 802.11 NICs featuring PXE firmware, the Ethernet-to-wireless bridge is the only way to go to provide wireless network booting.

The thin client has the PXE firmware in the Ethernet card which is connected to the Ethernet-to-wireless bridge. Thus, when the thin client broadcasts the PXE request it is bridged and forwarded to the wireless network access point, which in turn is connected to the wired network where the servers reside.

This solution is completely transparent for the thin client and servers.

Wireless security


Wireless security (ESSID, WEP, WPA, etc.) can be configured in the bridge so there's no need to store nor configure theses settings in the thin client.

History


I've successfully implemented this approach in the past in some large scale PXES Universal Linux Thin Client deployments, in big retail stores mainly with moving thin clients (battery operated thin clients mounted on a cart).

External links


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