Wake on Lan with ip-helper and ip directed-broadcast

[Hinrich_S]

Hi,

i am currently facing problems regarding the "ip helper-address" and "ip directed-broadcast" functions.

My plan:

I'd like to wake up some clients via wake on lan (wol). These Clients can be either in Vlan 1 or in Vlan 64. My wol-server is in vlan 64. Unfortenately the server doesnt have many configuration options. So the network has to do the job. The wol-server sends a wol broadcast (udp port 2304) in vlan 64. I'd like to "copy" this broadcast into Vlan 1.

My configuration:

wol-server ip: 10.203.64.19

Router:

interface Vlan1

ip address 10.253.0.2 255.255.248.0

ip directed-broadcast

interface Vlan64

ip address 10.203.64.2 255.255.255.0

ip helper-address 10.253.7.255

ip directed-broadcast

ip forward-protocol udp 2304

Result

I use Wireshark on a Client Vlan 64. I can see two packets in vlan 64. Both from 10.203.64.19. The destinations are: 10.203.64.255 and 255.255.255.255.

At the same time there is no packet in Vlan 1.

Question

To my knowledge the Broadcast in Vlan 64 should be sent to the broadcast address of vlan 1 by the ip-helper. The "ip directed-broadcast" in vlan 1 then should broadcast the packet in vlan 1. Is there an error in my configuration?

[shillings]

Do you have 'no service dhcp' configured? If so, enter 'service dhcp'

[Hinrich_S]

I dont want to use DHCP on this router.

There is no result when I run the command "show running-config | include dhcp".

Do I need the "service-dhcp" to use "ip helper-address" in combination with "ip directed broadcast"?

[shillings]

Do I need the "service-dhcp" to use "ip helper-address" in combination with "ip directed broadcast"?

You need 'service dhcp' configured for the 'ip helper-address' command to properly function.

It's the default command, so provided you can't see 'no service dhcp' in the config, then it must be enabled.

[devils_advocate]

What options do you have when sending the WoL packet?

When using IP directed broadcast, the Layer 3 destination address will be the broadcast address of a single subnet, hence why its only recieved on one Vlan.

[Rolf Fischer]

As far as I see the configuration is exactly how it should be, so please forgive me my silly question:

Are you sure that 2304 is the correct port number?

Apart form that I'm running out of ideas...

You don't have any access-list in your SVI-configs, do you?

Do you see the counter for forwarded broadcasts increasing in "show ip traffic | b ^UDP"?

Just for the fun of it you could try another ip helper - Cisco routers normally accept the all-1s and the all-0s as well:

interface Vlan64
 ip helper-address 10.253.0.0

Best regards

Rolf

P.S.: A Cisco WoL Doc: http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a008084b55c.shtml

[Hinrich_S]

I'm sure that 2304 is the correct port number, because i can see the packets in my Wireshark trace.

I'll try the "ip helper-address 10.253.0.0" on monday when I'm back in the office, thank you.

[Rolf Fischer]

In the meanwhile I tried your setup with gns3 simulating the WoL server by a router that sends it's syslog messages to 255.255.255.255 using port 2304 and it works just perfectly (as expected).

Two more notes:

1) You don't need to enable ip directed broadcast for VLAN 64 (you had a limited BC in your capture as well)

2) If you have it working, I'd recommend to limit the ip directed broadcast for VLAN 1 by an extended access-list allowning only the WoL server as IP source and UDP port 2304.

Best regards

Rolf

[Hinrich_S]

Hi, I've got the solution to the problem.

The configuration works perfectly fine after removing and reconfiguring the ip helper addresses. Thank you fischer.rolf for your effort and your additional notes. It's a good idea to limit the clients that are able to use the directed broadcast.