FROM THE IGLOO

We have had some people asking questions about Wake On LAN in our products lately, and I thought that a quick post regarding what we are doing in the different products might be helpful to clear up some of the mystery surrounding Wake on LAN in our software. A lot of people see it as some black art but it’s really not that bad.

In our products we use two types of packets that we send out to wake a machine up, a directed packet, and a subnet directed broadcast. Now most environments don’t support broadcast between subnets, in fact according to a RFC document from August 1999 routers ship with the ability for broadcasts to pass through them disabled. Our Core Console product is able to work around this by using what we term a Wake on LAN relay, in essence we find a computer on the same subnet that the system you are trying to wake up and we use that computer to broadcast the WOL packet. While this will require that a system running our Core Agent is up and running on that subnet it allows the Core Console to wake up computers across subnets without turning on broadcasting on the network.

Our Deep Freeze product however does not have the ability to use a Wake on LAN Relay, and because of this behavior we can get into a situation where the behavior of Wake on LAN looks completely random. In effect if you are testing Wake on LAN by shutting a computer down and then attempting to wake it up right away it will work, but if you shut the computer down and come back the next morning and try to wake the computer up it won’t respond. What is happening is that the broadcast packets are being blocked but the directed packet is getting through when the testing is done right away, however once the ARP Cache that tells the directed packet where to go expires neither option can wake the computer up.

Now it is possible to turn on Broadcasting in your network if you have the appropriate gear in place, but it’s probably a really good idea to have a talk to the folks that manage your network before doing so. If you are the person managing the network, and you don’t know why broadcasting is turned off in the first place it’s probably better to leave it be, or give the support team here a call and we can talk to you about why you may or may not want to turn this option on.