Hello Everyone, I have questions few questions regarding WOL. 1- In case of Subnet Directed Broadcast, we would require all the routers between SCCM Site Server and Clients to allow broadcast from SCCM Site Server to all the clients over UDP Port 9? 2- As for the Unicast, no change would be required on the network infrastructure? 3- The ARP Cache in the switches is only for 5 minutes; and after that there is no information of any machine on the network at the switch so if we send a magic packet either through broadcast or unicast, how would that reach to the target machine as the switch would have no information about the MAC address? 4- What is general recommendation for WOL, Unicast or Broadcast? I know microsoft recommends broadcast, but what is more practical. Thanks in advance.

1. Correct 2. Correct. 3. ARP caches have nothing to do with WoL packet delivery fro a ConfigMgr persepctive for either method as both use the MAC address from hardware discovery: http://technet.microsoft.com/en-us/library/bb693568.aspx, http://technet.microsoft.com/en-us/library/bb632807.aspx. Of course if the layer 2 device in the last hop of the journey involved in unicast WoL cannot translate the IP Address to a MAC address, then of course the WoL packet can't be delivered -- this has nothing to do with ConfigMgr though, it's networking 101. This is not an issue with subnet direct broadcast WoL though. 4. Broadcast because Unicast has multiple scenarios including the ARP Cache as well as the client no longer having the same IP Address among others where it breaks down. Broadcast is consdier by some a security risk, but this can be mitigated by only oallowing cross subnet broadcasts from your site server. http://blogs.technet.com/b/smsandmom/archive/2008/03/04/configmgr-2007-implementing-wake-on-lan-wol.aspxJason | http://myitforum.com/cs2/blogs/jsandys | Twitter @JasonSandys

.Thanks for the response. My only concern is ARP Cache. Yes, it has nothing to do wiht the SCCM, but it affects WOL functionality. No matter which method is used for WOL either Unicast or Broadcast, if the machine is down for more than 5 Minutes, its information would not be available at the switch so how would the packet be delivered to the target machine? I hope I have got my question across

Actually, with a broadcast, the ARP cache is not involved. That's the whole point of a broadcast, it goes to every NIC in a specific subnet/broadcast domain because it (the last hop layer 3 device) does not know who it should specifically be delivered to. Each NIC that receives the broadcast evaluates the "message" and in the case of WoL, it compares its own MAC address with that in the "message" (aka the magic packet). If it matches, then it wakes up the system. Are there still weakness with a centralized WoL scheme like that implmented by ConfigMgr: yes. That's why there are third-party products like Adaptiva's Green Planet and 1E's Night Watchman.Jason | http://myitforum.com/cs2/blogs/jsandys | Twitter @JasonSandys

Thanks Jason for the reply. Broadcast is the word that causes havoc when you are with the network guys. Their usual concern which is also right is that if we allow broadcast from SCCM Site Server and if this machine gets compromised then this machine can cause hell on the network. So, it is very hard to convince them to allow Broadcast from any machine on the network. It is political as you know. Anyways, if we have unicast in place then the maximum time that we have to bring the machine online from WOL is 5 minutes? Correct me if I am wrong? As it is performed based on inventory data and if ARP Cache is cleared, simply the package would not be received by the target client. Thanks.

As I said above WoL is a flawed technique at best. However, that's where third-parties come into the fold and I highly recommend you explore their products. Alternatively, have you researched using the wake up features and power management in R3? These may accomplish your goals also -- just in a different way. Intel's AMT/vPro solution also provides a possible solution as it does not use WoL to wake up systems.Jason | http://myitforum.com/cs2/blogs/jsandys | Twitter @JasonSandys

Thanks for the reply. I will definitely look into the R3 Power Management feature. But, with respect to WOL no matter which system we use either SCCM or SolarWinds, etc., we would still be facing the same situation as the problem lies with the ARP Cache that is maintained on switch which by default is 5 minutes. So, if I have understood correctly, in a unicast WOL, we only 5 minute window for success. Correct me if I am wrong. Cheers.

Potentially. The third-party products from Adaptiva and 1E use peer-to-peer WoL solutions using local nodes on subnets that harvest and maintain MAC addresses so that they not have to rely on just in time ARP requests to send the magic packets.Jason | http://myitforum.com/cs2/blogs/jsandys | Twitter @JasonSandys

Thanks for the quick response. So, in case of unicast SCCM, my concern is valid? Secondly, the products that you mentioned if they require an additional nodes on the network just for WOL then from cost perspective, such solutions could be expensive. What is more practical of the two. SCCM WOL with Broadcast or Thrid Party Solutions considering cost a major factor. Thanks in advance.

Yes, your concern is valid with ConfigMgr or any centralized WoL solution. For the peer-to-peer solutions, "peer" workstations are used so there would be no extra cost there except for the licensing cost of the solution itself. Don't know what's more practical for your org -- only you can make that decision. The third-party offerings have technical advantages but do add cost.Jason | http://myitforum.com/cs2/blogs/jsandys | Twitter @JasonSandys