Wake on LAN across local subnets/VLANs

Recently we had a client trying to Wake on LAN (WOL) across local subnets/VLANs. All of the routers and switches were cisco equipment. The WOL would only work on the local VLAN but not to other VLANs (or subnets) that were trunked out in other areas. The solution was a simple fix of a few commands on the local and remote subnet routing/switching devices.

Wake on LAN Solution:

  1. An IP Helper needed to be configured on the WOL packet sending network pointing to the receiving network.
    1. L1(config-if)#interface vlan 2 ? Interface of network you are sending packet from
    2. L1(config-if)#ip helper-address 172.16.3.2 ? Gateway of receiving network
  2. The IP protocol needed to be forwarded (in the case UDP port 7)
    1. L1(config)#ip forward-protocol udp 7
  3. An ACL needed to be configured as to only allow the WOL ports required
    1. L2(config)#access-list 101 permit udp any any eq 7 ? you can also specify host and/or destination instead using any any
  4. An IP Directed-Broadcast needed to be assigned on the receiving network
    1. L2(config-if)#ip directed-broadcast 101 ? 101 references the ACL that allows/restricts the broadcasts going through. This rule enables translation of directed broadcasts to physical broadcasts on the network where the WOL target is located.

Repeat this process as needed for each network that needs to send/receive WOL packets.

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