enable broadcast forwarding

[mohammed hashim]

hi,

I am using an application which uses "net view" command to discover all computers in the network.

net view is a windows command and it does use (as to per my knowledge) netbios-dmg (port 138)

the thing is that, all the computers which is in the same broadcast domain are discovered all, but other computers in other broadcast domain are not. I guess this is because L3 device does not forward broadcast by default.

I was thinking about ip helper-address, but this command is useless in my case because it unicasts whatever broadcast packet it receives to a specific IP address.

what I want is to enable the server to discover all computers in all broadcast domains (through net view windows command)

any idea how to do this on cisco devices !?

thanks,

[Bilal Nawaz]

Mohammed, under the SVI or interface where the other computers are based, you can configure an "ip directed-broadcast" referencing an ACL which will match the packet of what the server sends out.

If the server aims to broadcast on a subnet by subnet basis. It depends on the server's behavior. The problem with this is you must specify some sort of subnet address or broadcast address for the discovery.

I don't know much about the application so can't suggest a certain solution.

Bilal

[mohammed hashim]

hi Bilal

I did this but unfortunately did not work, the server did not show any results on other.

what Tshoot can I use to see the status after enable  ip directed-broadcast ??

[Richard Burts]

The suggestion of ip directed-broadcast is helpful but is only part of the solution. You also need to use ip helper-address on the SVI for the VLAN where the server is connected. You are not correct that helper address always sends unicast packets. You can configure helper address to forward a directed broadcast. For example you could configure something like this

ip helper-address 172.16.1.255

This will forward a single packet toward that subnet and when it gets to the interface where the subnet is connected it will send it as a local broadcast on that subnet (assuming that ip directed-broadcast is enabled).

HTH

Rick

[edit] If you want to check the status after configuring directed broadcast then use the command show ip interface <interface_ID>. That should show whether directed broadcast is enabled or not.

[mohammed hashim]

thanks for your reply,

but again did not work, I did exactly what you told me,

but again whne I use net view command in windows server, it shows me only machines in same its vlan,

I tried to take one computer from server Vlan, and put it in another vlan, server was again not able to see it (using net view).

Note: pinging works fine between all Vlans,


any other tips !?

[Richard Burts]

The fact that ping works between all vlans says only that you have correctly configured unicast routing. It says nothing about forwarding broadcasts.

If net view is not finding PCs in remote vlans it seems to me that there are two possible causes

- perhaps net view does not use UDP 138 as stated in your original post. Perhaps you can do a packet capture with Wireshark on the vlan where the net view originates and verify what protocol port it is using.

- perhaps you have not done the configurations quite in the way that we describe. Can you post the complete interface configuration for the vlan interface where net view originates and the interface where the remote device is that you want to discover.

HTH

Rick

[muneer012k]

Hi Richard,

Muneer here...!!! I am using net view command in a multi vlan environment. When I apply this command on VLAN 10.132.192.0/22 then it just shown 10.132.192.0/22 subnet PCs so please tell me what I will do that this command will show all the network PCs without enabling any broadcast.

Please note that net view command will only be used from a single PC (10.132.192.13) of subnet 10.132.192.0/22.

Kindly reply. Waiting for your response.

Thanks & Regards,

Monir Uddin Mazhar

[Richard Burts]

Muneer

Perhaps you did not understand what I was explaining, or perhaps I do not understand what you are looking for. net view uses local broadcast to discover other computers in the local subnet. If you want to discover computers in remote subnets then you need to enable forwarding of the local broadcast to the remote subnets. I do not believe that it is possible to discover computers in remote subnets using net view without enabling forwarding of the broadcast.

HTH

Rick