Cannot receive broadcast messages

[bkelly]

I am having a network problem. The prime indicator is that I cannot receive broadcast packets on my desktop.

Specifics: Using Microsoft Visual C# Express I obtained some demo code and built a UDP talker and a UDP listener. (Two separate programs.) I start up both on my desk top running XP Professional. Then I start both on my laptop running XP Home. Messages sent from the desktop are received by the laptop, but not the desktop. Messages sent by the laptop are received by the laptop, but not the desktop. Both are connected to a Belkin wireless router though a hard connection, then to a cable modem. Both have internet access. The Belkin router connects to a broadband cable modem.

I began investigating the problem with Start | Windows Firewall and I get the message “Windows Firewall settings cannot be displayed because the associated service is not running. Do you want to start the windows Firewall/Internet Connection Sharing (ICS) service?”

I click the Yes button and get the response: Windows cannot start the Windows Firewall/Internet connection sharing (ICS) service. Unfortunately, I just cannot find the buttons that say “Why not?” and “Do it anyway!”

So I go to Control Panel | Network Connections and find “Local Area Connection 2.” Although it contains a “2” in the name, it is the only entry in Network Connections. There I double click or right click on this “Local Area Connection 2”, and Control Panel locks up. It won’t respond to anything, it won’t resize, it won’t move, it won’t do anything. I have to use task manager to get rid of it.

Oops, I just found that it I leave it alone for a few minutes while I write this, the window kind of blinks then I can use the back button to get back to Control Panel. But if I click Local Area Connection 2, it locks up again.

What can I do to enable receipt of broadcast message on my desktop computer?

Thanks for your time.

[Davelray]

Sounds like you actually have two problems.

In regards to broadcast messages:
If you are connected to a "switch" instead of a "hub," you will not recieve broadcast messages. Switches are intelligent and route packets differently than a standard hub. A hub broadcasts packets to everything connected to it. A switch, however, will only send packets to the appropriate destination. This reduces crosstalk and collisions on the network and would also prevent your program from listening to any packets that were not specifically directed to that computer.

Regarding your network connection in Windows:
Possibly corrupted drivers for your network device. Try uninstalling your network card, reboot, then reinstall the drivers when it finds the card again.

Hope this helps,

[bkelly]

Hello David,
Thanks for the response.

Regarding the switch versus hub, I am not sure of the difference between switch and hub, but I have a router. I am now reasonably certain the problem is not in the router.

Since posting this thread I have continued work. I now have three computers involved, desktop, laptop, and proto. (An embedded computer on a prototype board that reads some sensors and outputs data on the ethernet LAN, use proto for short) All three plug into the router which is also plugged into my cable modem.

The proto is now reading its sensors and sending data out via broad cast messages. The laptop captures and displays the messages and I can verify that the data is correct. When the identical program is running on the desktop, it captures nothing.

As noted in the original post, the laptop can send and receive from itself and from the desktop and from the proto. The desktop can send and the laptop receives, but the desktop does not receive. The problem is clearly in the desktop.

Regarding drivers, that would be a line of investigation, except there is a problem. When I upgraded my desktop to XP Pro, video and network failed utterly. Video was old VGA and text based and there was no networking. I had to use my laptop to get all kinds of drivers and had to mess with it intensely to get it working. I saved all the downloads on CD ROM but I don't want to go through that again. Communications is working on the desktop as I write this on the desktop and do all my web surfing on it. I REALLY don't want to reload it. I would almost buy a new computer and try Linux before I reload this thing.

While that nuclear bomb approach is often the standard way of fixing Microsoft OS problems, I very strongly suspect that someone, somewhere, knows what this is and how to fix it. Everything works, including sending broadcast messages, except receiving broadcast messages. There is something in here that walks and talks like a firewall and I need to configure it. But I cannot find it.

But, you may well be right. With as much trouble as I had with drivers. I may have a driver problem. I really don't want to reload this thing.

Thanks again for your reply.

[Davelray]

Well, there is always a way around reloading. It usually boils down to which is "easier." You can start by first eliminating the normal startup programs. If they aren't intefereing, you will have to start disabling startup services. There are many guides on the internet for taking you safely through disabling windows services. My advice for disabling services is look for the obvious, and go one by one. One other thing to try is maybe a new network card in the desktop. One that uses a completely different chipset and driver from the one you are using now. This bypasses having to troubleshoot the existing network card and driver. I've seen network cards do strange things when their driver gets corrupted or they start going bad.

[Lord Soth]

Hi,

Sounds like you actually have two problems.

In regards to broadcast messages:
If you are connected to a "switch" instead of a "hub," you will not recieve broadcast messages. Switches are intelligent and route packets differently than a standard hub. A hub broadcasts packets to everything connected to it. A switch, however, will only send packets to the appropriate destination. This reduces crosstalk and collisions on the network and would also prevent your program from listening to any packets that were not specifically directed to that computer.

Regarding your network connection in Windows:
Possibly corrupted drivers for your network device. Try uninstalling your network card, reboot, then reinstall the drivers when it finds the card again.

Hope this helps,

Actually Switches divides/creates collision domains not broadcast domains. Which means layer 2 broadcast messages (UDP is layer 4 but will come to that too) can pass through switches but not through routers (or across subnets in other words). DHCP being a UDP based broadcast based protocol works before acquisition of an IP address and all layer 3+ broadcast protocols including DHCP also specify the layer 2 broadcast adress which is FF:FF:FF:FF:FF:FF in addition to layer 3 broadcast address.

Loren Soth

[Lord Soth]

Hi,

Hello David,
Thanks for the response.

Regarding the switch versus hub, I am not sure of the difference between switch and hub, but I have a router. I am now reasonably certain the problem is not in the router.

Since posting this thread I have continued work. I now have three computers involved, desktop, laptop, and proto. (An embedded computer on a prototype board that reads some sensors and outputs data on the ethernet LAN, use proto for short) All three plug into the router which is also plugged into my cable modem.

The proto is now reading its sensors and sending data out via broad cast messages. The laptop captures and displays the messages and I can verify that the data is correct. When the identical program is running on the desktop, it captures nothing.

As noted in the original post, the laptop can send and receive from itself and from the desktop and from the proto. The desktop can send and the laptop receives, but the desktop does not receive. The problem is clearly in the desktop.

Regarding drivers, that would be a line of investigation, except there is a problem. When I upgraded my desktop to XP Pro, video and network failed utterly. Video was old VGA and text based and there was no networking. I had to use my laptop to get all kinds of drivers and had to mess with it intensely to get it working. I saved all the downloads on CD ROM but I don't want to go through that again. Communications is working on the desktop as I write this on the desktop and do all my web surfing on it. I REALLY don't want to reload it. I would almost buy a new computer and try Linux before I reload this thing.

While that nuclear bomb approach is often the standard way of fixing Microsoft OS problems, I very strongly suspect that someone, somewhere, knows what this is and how to fix it. Everything works, including sending broadcast messages, except receiving broadcast messages. There is something in here that walks and talks like a firewall and I need to configure it. But I cannot find it.

But, you may well be right. With as much trouble as I had with drivers. I may have a driver problem. I really don't want to reload this thing.

Thanks again for your reply.

For unicast layer 4 (TCP or UDP) messages you should have no problem; for broadcast messages as you use a router it creates/divides separate broadcast domains. Unless you configure all the devices IP (including router's interfaces) to them same subnet you won't be getting the broadcast messages across the router. Luckily you have all your devices IP configured/configurable because when using DHCP you start with no IP address (which isn't your case, i.e. : sender ip : 0.0.0.0 dest ip : 255.255.255.255 dest mac : FF:FF:FF:FF:FF:FF) which can't pass through router at all. (So they invent DHCP proxy servers or DHCP forwarders)
If your prototype boards dictate a subnet, you should configure the rest of your equipment (PCs) to the same subnet for cross router broadcast to work.

Loren Soth