WoL Across VLANs: Directed Broadcast and WoL-Server Helpers

300-420 By islever Editorial Last updated

Design campus Layer 2 infrastructures

Short answer

AE Enable directed broadcast and forward-protocol on client-subnet interfaces, and WoL-server helpers on those SVIs, so magic packets reach sleeping clients.

Question

A customer plans to deploy WoL in the enterprise with these high-level design requirements: • DHCP services must be available • Clients BIOS settings must be set for WoL • Clients get IP addresses once online • Spanning-tree PortFast is enabled on the Layer 2 switches Which two solutions must the customer select to have a successful deployment? (Choose two.)
  1. IP directed broadcast and forward-protocol must be enabled on all the SVI or routed interfaces where the client subnets reside Correct Answer
  2. IP directed broadcast and forward-protocol must be disabled on all the SVI or routed interfaces where the client subnets reside
  3. IP helper-addresses for the client ranges must be disabled on the SVI or routed interface where the WoL server subnet resides
  4. IP helper-addresses for the WoL server must be enabled on the SVI or routed interface where the client subnets reside
  5. IP helper-addresses for the client ranges must be enabled on the SVI or routed interface where the WoL server subnet resides Correct Answer

Key Takeaways

WoL across VLANs needs two pieces: directed-broadcast allowed on client interfaces (A) + a helper on the client SVIs that relays the WoL server's packets (E). Disabling either (B/C) breaks delivery.

To wake clients across subnets, enable IP directed-broadcast and ip forward-protocol on the routed/SVI interfaces where the client subnets reside (so the subnet broadcast is forwarded), and enable IP helper-addresses pointing to the WoL server on those client-subnet interfaces so the server's magic packets are relayed into each client VLAN.

Common mistake: Picking D: the helper must point FROM the client-subnet SVI TO the WoL server, not the reverse; E (helper for client ranges on the WoL-server subnet SVI) is the correct direction. B and C disable the needed features.

Expert Analysis

Why the Answer Is Correct

A and E are correct. WoL magic packets are broadcasts; to cross VLANs they must be forwarded as directed broadcasts, so IP directed-broadcast and ip forward-protocol are enabled on the client-subnet interfaces (A). The WoL server sits in another subnet, so IP helper-addresses for the WoL server are enabled on the client-subnet SVIs to relay its packets (E).

Why the Other Options Are Wrong

B and C disable the required features, breaking delivery. D points the helper the wrong way (from WoL-server subnet toward clients rather than enabling the relay on client SVIs), so it does not deliver magic packets to the sleeping clients.

Community Comment Notes

The vote is AE (75) vs AD (25). Commenters cite Cisco's WoL-across-VLANs guide: enable directed broadcast on client interfaces and configure the WoL-server helper on those SVIs.

Official Reference

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91672-catl3-wol-vlans.html

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Community Votes

AE
75%
AD
25%

75% of anonymous learners picked answer AE. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. cf57f86 👍 2
    AE are correct. https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91672-catl3-wol-vlans.html
  2. 26d13e9 👍 1
    D would be correct only if the WOL server is the DHCP server. You have to configure helper on the WOL server router interface that will allow the WOL server to reach the subnet of the WOL client. Normally, ClientSubnet.255 for all WOL subnets. So...option E in this case.
  3. cybman76 👍 1
    A&D is correct

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