Wake on LAN over different VLANS

[Wayne Workman]

That’s a pretty awesome plugin… for real…

I’m going to use that when I setup FOG in vmware at our central site.

[szecca1]

@Tom-Elliott I apologize in advance but where would I get this broadcast ip? Would this be the gateway ip from each building? I’m not sure where to pull this broadcast IP from?

[Wayne Workman]

@szecca1

You basically jot down any valid IP for a network, then jot down your subnet mask.

Convert both to binary, with each of the four octets separated by a decimal as normal.

Then, for each ‘0’ in the subnet mask, you’d flip that to a 1, but you’d still use the network portion of the valid IP, those binary bits would just “fall through”

So… example time…

Subnet mask: 255.255.240.0

IP 10.2.3.8

Binary IP Subnet:

00001010.00000010.00000011.00001000
11111111.11111111.11110000.00000000

(Client IP network portion: 00001010.00000010.0000 Client portion: 0011.00001000)

the fall through numbers for the network address:
00001010.00000010.0000000.00000000 (Where 1 is set in the subnet mask, binary from the client ‘fall through’ to form a network address)
This gives us a network address of 10.2.0.0

The broadcast address is the network address combined with all-on client bits.
00001010.00000010.00001111.11111111
(binary in the subnet mask set to ‘0’ ‘fall through’ to the broadcast address as ‘1’)

Convert to decimal: 10.2.15.255

So, 10.2.15.255 would be the broadcast address for that IP and that subnet mask.

And, that’s correct, that’s my particular building’s broadcast address.

[szecca1]

@Wayne-Workman The 10.2.3.8 address that you used in your example, where did you get that from? Is that just a random IP of a client in the 10.2 VLAN or is that something in particular?

[Wayne Workman]

@szecca1 It’s a random (but valid) IP for my network.

Also, don’t think of it as a V-LAN… that’s not correct. Think of a “network” as a broadcast domain, or a subnet.

V-LANs came along WAY after the specs for TCP/IP and routing were developed. V-LANS are just a way to logically separate traffic within the same device.

V-Lans have just numbers assigned… I.E. 5, 6, 7, 8, 55, 56, and so on.

Networks have a network address, and a broadcast address and a valid range (hence ‘broadcast domain’). If you have subnetted networks, then I SUPPOSE its ok to call them subnets… but I won’t call them that lol.

[szecca1]

@Wayne-Workman Ok I am stuck using your example so I pulled a random IP from my high school.
Subnet mask: 255.255.0.0
IP: 10.2.1.64

Binary IP Subnet:

00001010.00000010.00000001.01000000
11111111.11111111.00000000.00000000

(Client IP network portion: 00001010.00000010.0000 Client portion: 0001.01000000)

Which the fall through for the network address if I am correct would be:
00001010.00000010.00000000.00000000
which give a network address of 10.2.0.0

After that I am not sure where to go as I get confused by what you did.

[Wayne Workman]

@szecca1 said:

@Wayne-Workman Ok I am stuck using your example so I pulled a random IP from my high school.
Subnet mask: 255.255.0.0
IP: 10.2.1.64

Binary IP Subnet:

00001010.00000010.00000001.01000000
11111111.11111111.00000000.00000000

(Client IP network portion: 00001010.00000010.0000 Client portion: 0001.01000000)

Which the fall through for the network address if I am correct would be:
00001010.00000010.00000000.00000000
which give a network address of 10.2.0.0

After that I am not sure where to go as I get confused by what you did.

IP: 00001010.00000010.00000001.01000000
Subnet: 11111111.11111111.00000000.00000000
(only where there is a 1 for subnet, the IP address portion falls through)
Fall through: 00001010.00000010.00000000.00000000 <-- your network address

To get the broadcast, turn on all the client portion ‘bits’ where the subnet mask is 0.

00001010.00000010.11111111.11111111 <-- your broadcast address 10.2.255.255

[szecca1]

@Wayne-Workman And that broadcast address should allow me to run the wake on lan to the high school which is where that IP came from?

[Wayne Workman]

@szecca1 said:

@Wayne-Workman And that broadcast address should allow me to run the wake on lan to the high school which is where that IP came from?

It should. Test it and report back? I am not using the plugin yet so I don’t know, but if Tom says that’s how it is, then 99.9% of the time, that’s how it is.

[szecca1]

@Wayne-Workman

This is what I entered into that plugin creating it for my high school and just tested it and didnt work.

[Tom Elliott]

You likely need to allow udp-broadcast-forwarding on your switches. At the very least, it needs to be enabled for the routing switch. The way to do this varies depending on the switch. HP Procurve allows for udp-broadcast-forwarding on (I think)

[szecca1]

@Tom-Elliott We already did that thinking it was a switch problem before doing this plug in

[Tom Elliott]

@szecca1 are you 100% sure that 10.2.255.255 is that networks broadcast address?

[szecca1]

@Tom-Elliott I worked with @Wayne-Workman and he helped me figure that out by converting an IP address into that. Previous posts go through it and thats what we came to the conclusion it is.

[Tom Elliott]

What is the subnet mask of your network? Class A, B, C?

[szecca1]

@Tom-Elliott Subnet mask is 255.255.0.0, class B

[Wayne Workman]

@Tom-Elliott said:

@szecca1 are you 100% sure that 10.2.255.255 is that networks broadcast address?

If the info he gave me is correct, I can assure that what we came up with is correct, but feel free to doublecheck my work using third party tools: http://www.subnetonline.com/pages/subnet-calculators/ip-subnet-calculator.php

[szecca1]

@Wayne-Workman As long as all you needed was a random IP address and the subnet that info is correct. The only thing weird is the website you sent is saying we are a class A even though we are a class B.

[Tom Elliott]

That’s often the case class a class B classy are usually directed by the first octet one through 126.whatever is considered class a, 128.whatever through 191.whatever is considered class b,192 up is class c

[szecca1]

@Tom-Elliott ok that makes sense, and I ran another test and still wake on lan is not working. At this point I am not sure what to do. The imaging works perfectly but the clients have to be on in order for the imaging to go through, obviously.