Most command-line tools to generate the WoL Magic Packets send them as UDP datagrams and set the destination IP to the limited broadcast address 255.255.255.255, thus those Magic Packets are never routed (Scope = local subnet).
Thats why you need in this case the ip-helper command, which converts (local) UDP broadcasts of serveral well-known protocols (DHCP, TFTP, DNS, NetBIOS, TACACS) into unicasts and then forwards them to the helper address.
Since the portnumbers typically used by WoL tools (7, 9, 12287 [0x2FFF], ...) are different from those used by the well-known protocols, you'd also need the 'ip forward-protocol udp <number>' command to make it work.
Some tools, like SolarWinds Wake-On-LAN, allow you to send IP-Packets immediately to a directed broadcast IP outside the local subnet. In this case it is sufficient to allow directed broadcasts on the client's SVI(s). For security reasons, you should limit this with an ACL to the WoL server IP and portnumber:
access-list 100 permit udp host <server-ip> any eq <port-number>
!
interface Vlan <client-vlan>
ip directed-broadcast 100
!
If the tool doesn't allow to set the destination IP to a directed broadcast, you'll need some additional configuration:
ip forward-protocol udp <port-number>
!
interface Vlan <WoL-server>
ip helper-address <directed BC-address client-vlan>
!
HTH
Rolf
