Wake on LAN across Layer 3

[rwilletts]

When setting up WOL across a Layer 3 boundary you have to enter an ' ip helper ' address on the WOL server L3 vlan for each subnet you want to ' wake '.

What if you have 200+ subnets , I'm fairly sure the practical limit for ' ip helper ' addresses is 16 ?

[paolo bevilacqua]

Maybe the WOL server should be configured to send to the direct broadcast address of each remote subnet ?

Or you expect the router to perform packet replication at no configuration and processing cost ?

[Richard Burts]

I wonder where the original poster got the idea that the practical limit for ip helper-address was 16? I agree that there is some additional overhead on the router for each helper-address that you add to the configuration. But a router should be able to process a lot more than 16 helper-addresses.

200+ would be a lot of helper-addresses and depending on what kind of router (how much CPU does it have) and what other features are configured doing 200+ might be a stretch. But most routers should be able to do lots more than 16.

HTH

Rick

[rwilletts]

Quote from a previous TAC case ;

DHCP processes first 16 'ip helper-address' entries as per the order of configuration

[paolo bevilacqua]

I tend to agree with Richard. I guess some practical testing would be needed.

[louisroggo]

I just tested this in my environment and if the WOL server sends out a directed broadcast there is no need for the helper addresses on the Wake On LAN server environment.  The only thing you need to do is enable ip directed-broadcast oon the client subnets.  Microsoft SCCM is capable of this, and you can find a free utility to test such as WOLcmd.exe that also performs directed broadcasts.