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Remote Controlling Your LAN

LAN users can remotely wake up the nodes on their network, run a certain process and put them to sleep all of this by using the Wake on LAN technology.

Today's networked environment is more powerful than ever. This makes the network administrator's job more complex. As an administrator, you can't take full advantage of the networked environment unless it is effectively managed.

Consider the following situation: you have upgraded all the PCs that needed more memory, disk or processing power on your network. Now you're ready to install the software.

There are three options that you can consider here:

  • Request all users to install the software themselves.
  • Send numerous messages asking all the users to leave their PCs switched on overnight and send the technician around do a manual install on each PC during the night.
  • Write a script that runs during off-hours, remotely turns on each PC, installs the application and turns the machine off again.

The first option cannot ensure that all users have upgraded. Also in the process it would affect productivity of the end user. If you adopt the second, it takes care of the two issues quoted above but involves a huge amount work for the technical staff. To avoid disrupting users and overwhelming the network during prime work hours, you would like to have your technicians install it automatically at night. Ideally, adopting option three can reduce your network management headaches, raising productivity in the process.

You can achieve this by using a technology called Wake on LAN. It is one of the most powerful desktop management technologies that a network administrator can employ.

Remote wake-up feature, combined with other remote management capabilities, gives network administrators the ability to switch machines on remotely and automatically during off-hours, to perform any remote management activities. The system can be automatically powered on from a fully powered off state over the network. Once the system is awake, it can be directed to run utilities such as virus scan or disk backup, or install software upgrades, and then return to a sleep state. The combination of off-hours wake-up and remote access allows network administrators save time on automated software installations and upgrades, in the process increasing end-user productivity by avoiding disruptions during work hours.

Remote Wake Over Network

Remote Wake up, also known as Wake on LAN technology, was a result of the need for better management of power on PCs. Earlier; PCs never had any power management built-in. A PC could only be powered ON or OFF manually by the user. As a result, remote management of PCs was difficult.

If a network administrator wants to remotely manage PCs during off-hours, then users have to keep their PC switched on in anticipation of maintenance. This resulted in lot of power wastage. As a result of this, PC vendors and OS vendors came out with technologies such as Advanced Power Management (APM) and Advanced Configuration and Power Management Interface (ACPI), where a PC can detect a state of inactivity and can be put in to a low power state where it consumes very less power. Or even the PCs could be shutdown when not in use.

Then came the question of how to turn on these PCs to full power mode remotely, when required for some remote management activity. The result of this requirement is Remote Wake up or Wake on LAN technology.

This allows a network administrator to start a system remotely using a LAN signal from a management console. It is achieved through ACPI where a system can wake from a low power mode in response to a specified network packet. When the system is turned off, the managed adapter continuously monitors the network and watches for a wake-up packet. When it receives that packet, it alerts the system, which then comes to full power-state and stands ready for any remote management tasks.

How Wake On LAN Technology works?
Wake on LAN technology involves a Network Interface Card (NIC)/ Modem that waits for a wake-up trigger from the network. When it receives the trigger it initiates system power up.

The trigger to wake-up the target machine can be recognized in multiple ways.

Magic Packet Technology
Wake on LAN originally used a technology known as Magic Packet, which sends a data packet directly to a system. This packet consists of data that has 16 repetitions of the system's media access control (MAC) layer address. The MAC address is unique to the network adapter in the system. So the Magic Packet wakes only the system targeted for start-up. When the network adapter receives and decodes this packet, it sends a power management event (PME) signal to the system that brings it back to full power and boots the system. This is BIOS level control.

Pattern Byte Matching (PMB) Or Packet filtering Technology
In a magic packet the wake-up packet is predefined and depends on the MAC address of the target machine. Hence, for waking up each individual machine on the network, a separate packet, containing its MAC address needs to be sent. As an alternative, if an administrator can configure his own set of packets for which a group of PCs can respond and wake up, it is advantageous to wake up a group of PCs with one single packet. This is achieved in Pattern Byte Matching or Packet filtering. PBM provides the wake-up packet for systems that support ACPI.

The system downloads a series of patterns, configured by the administrator, to the network adapter, which in turn monitors for the arrival of these patterns in a packet. If it finds these patterns, the network adapter generates a PME signal to wake up the system. In other words the system filters a defined set of data trigger packets from the network and takes action. This is more flexible than Magic Packet. In contrast to Magic Packet, which is a BIOS level control, this is an Operating System (OS) level control and hence can be much more flexible in its utilization.

Wake-on-Ring (WOR) Wake-up Technology
Wake-on-Ring makes it is possible to wake up your desktop PC remotely when the modem attached to it detects a telephone ring. After the modem detects the ring, the PC restores itself to full power. With this convenient feature, it is also possible to use your PC as a fax machine, telephone answering machine or remote data server.

Wake-on-link is a new wake-up technology designed for energy management under ACPI. All network clients on an Ethernet network depend on link state changes, or heartbeat pulses, to ensure continuous connection to the LAN. If the link is down or there is a break in network, the heartbeat pulse is interrupted. Under control of future ACPI-compatible operating systems, the absence of a heartbeat pulse can signal a sleeping network client to go into a deeper sleep state to conserve energy.

Re-establishing the network link state signals the client to transition to a lighter sleep state. These adjustments are designed to yield budget savings in large corporate networks. Today, many Wake on LAN-enabled network adapters support both wake-on-link and wake-up by Magic Packet.

Wake-on-link has limited functionality and is not expected to be widely adopted for several reasons. First, implementing wake-on-link in hardware is difficult and implementations can vary significantly. Second, wake-on-link yields marginal energy savings over current OS directed sleep states, because such a small percentage of network clients never lose their network links.

What Is Required To Make It Work?

You need the following hardware:

PCs: Choose a PC, which is designed for remote power control and the Wake on LAN feature.

Adapters: Choose a network adapter, based on the type of network (Ethernet or Token Ring) you use, which is Wake on LAN enabled. Then, when the user turns off the PC, an auxiliary power supply keeps the adapter active on the Ethernet or token ring network.

The sequences of events are as follows:

  • The Network administrator programs/ schedules a wake-up request from a management console at a specific time for a set of target PCs. Typically, the wake-up request is scheduled for after hours or weekends, times when demands on the bandwidth are low.
  • The program, which runs at scheduled time from Management Console, sends a wake-up request packet over the Ethernet or token ring network to all Wake on LAN-enabled target PCs.
  • The network adapter on the Wake On LAN enabled PC intercepts the wake-up frame and signals it to power up. The PC powers up and goes through its normal startup sequence.
  • In integration with any system management software, powered-up PC initiates the work that has been scheduled for it, like software installation.
  • Powered-up PC completes the work and waits for a period of inactivity and then goes into hibernation or sleep mode or can be remotely shutdown.

What Do LAN Wake-up Frames Do?
In the auxiliary-powered state, the adapters monitor LAN traffic for valid LAN wake-up frames. Token ring wake-up frames follow the industry-standard Magic Packet specifications, which means that their destination addresses can be one of these three types:

  • Broadcast: The destination address is all 1s and goes to all nodes on the network.
  • Multicast: The first bit of the address is 1, which identifies a group address for a group of workstations. Higher layer functions determine the group of workstations being addressed.
  • Individual: The destination address is the unique address of a node on the network.

The wake-up frame for a Wake on LAN-enabled adapter can have a broadcast, multicast or an individual destination address.

Each wake-up frame contains a unique data field, one that is not expected in typical LAN traffic. It contains an individual MAC address, the address of the Wake on LAN adapter in the target PC, which ensures that the frame is sent only to the PC at that address.

The wake-up frame format consists of these required contiguous sequences:

six bytes of F (XX'FF') followed by a 48-bit target address repeated at least eight times.

These sequences can appear anywhere within the wake-up frame, and you can modify any frames being sent over the respective networks to include them. When the micro code in the adapter detects these sequences, it sends a signal to the PC. The PC then turns on, just as if you turned it on using the On/Off switch. (see Figure-2)

Applications And Benefits

Consider a large organization with a huge number of desktops. Each evening when these businesses close, the desktops are powered down by users.

With the right PCs and network adapters, each workstation could be automatically booted up just when the employees arrive for work next morning and check in by integrating Wake on LAN technology with appropriate desktop management application. As a result of this:

  • No one would need to come in early to do that.
  • No one would have to wait during the power-up sequences.
  • No one would have to ask a customer to wait till his/her system boots.

A little increased productivity here, a little increased productivity there it all adds up.

Consider a sales person who covers the globe from Tokyo to Lisbon, from Nice to Venice, from Moscow to Jinzhou. Think what they could accomplish if they could access their workstations remotely. For example, by logging onto the Internet through their laptops, salespeople could start up their workstations each night to compile the inventory database for the next day's sales.

Then, they could upload the results and have them the next morning. For accomplishing this they need not keep their laptop always powered ON when they are travelling. They can start up their laptop only when required to complete their work remotely and then shut it down remotely. This is possible through Wake on LAN technology.

Consider situations such as these:

  • You rarely use a thermal wax printer, but you'd like it to be turned on and ready to use in 15 minutes.
  • You had 17 remote servers in 17 remote locations shut down in the last half hour. You need to restart them.
  • You have to turn on the print and file servers each morning, but they're scattered over several floors of an office suite. It typically takes you 45 minutes to get to all of them.

And the list grows. All these can be achieved with appropriate use of Wake on LAN technology.

Some of the benefits this technology can offer are:

A remote wake-up technology that enables you to remotely power systems "on" for off-hours maintenance. This technology, when used with appropriate Desktop Management application, helps save time on automated software installations, upgrades, disk backups, virus scans and such other scheduled remote management tasks. Equally important, it increases end-user productivity by moving such planned disruptions to off-hours.

By remotely initiating long routines such as inventory and asset management after hours and on weekends.

By analyzing and resolving support problems remotely.

By saving the time it takes to turn on all of the computers manually when you want to install the latest release of software on multiple machines.

  • By eliminating delays in or interruptions of users' "real" work.
  • By using Wake on LAN technology today, you can:
  • Power up your PC or multiple PCs from a remote location.
  • Manage networks more efficiently.
  • Save bandwidth during the day by transmitting large files at night.
  • Help your company save on its energy bill.
  • Eliminate trips back to work to troubleshoot a problem.
  • Be on the leading edge when new applications for Wake on LAN technology become available.

Once you begin thinking about the scope for today's applications for Wake on LAN technology, implement them and start reaping the benefits, a whole lot of new application areas are bound to come up bringing in immense productivity benefits to the organization.

Remote wake-up enables network
administrators to switch machines on remotely and automatically during off-hours, to perform remote management activities

The combination of off-hours wake-up and remote access allows network administrators save time on automated software installations and upgrades, and increases end-user productivity by avoiding disruptions during work hours

By using Wake on LAN technology today, you can save bandwidth during the day by transmitting large files at night

M S Rajashekhar, Software Development Manager, Network Management Technologies group, Novell, Bangalore. He can be reached at msrajashekhar@novell.com

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