Joe Taylor wrote:

Additional information: "ipconfig" on Windows, "ifconfig" on Linux, report the following IP addresses:

Computer A:
Computer B(1):
Computer B(2):
Computer C(1):
Computer C(2):

<Snip, reordered>

This works fine (but of course, still sends the heavy multicast traffic through the hub). If I remove this routing instruction and instead enter

# route add -net netmask dev eth1

<Snip, reordered)

 Connections to the Hub are assigned dynamic IP addresses;

I assume these addresses are in the 192.168.1.x range?

No, see above. I was probably wrong to call them dynamic IP addresses. They are assigned by DHCP, but I believe they are always the same.

I assigned hard-coded addresses and for the direct inter-machine connection
between B and C.

<End Snip, reordering>

I see.

These are likely dynamic, but assigned from the ISP IP pool based on the MAC address of the NIC requesting the IP. In a lot of cases, though they are dynamic, they hardly ever change as long as the MAC address of the NIC remains the same. Many cable ISPs do something similar on dynamic IP addresses. Though in your case, the actual Internet IP assigned is unimportant, as long as you get one assigned :) The addresses in the are private addresses as are the addresses.

Why did you use a mask of instead of in your multicast route statement on the Linux box?

(Your: # route add -net netmask dev eth1 statement.)

What is in /etc/network-scripts/eth(x).route?

Have you considered replacing the hub with a 100 Mbps full-duplex Ethernet switch? There are many advantages in this over a hub.

Yes. That was my first attempt at a solution. I tried replacing the 10 Mb/s hub with a 10/100 Mb/s switch. The result was the same: when Computer C was multicasting 16-bit Linrad data at about 0.77 MB/s, Computer A was essentially unable to use the internet. The switch apparently did not prevent multicast traffic from reaching A.

This was with a "D-Link 10/100 Desktop Ethernet Switch. I also tried it with a Linksys model EZXS55W "EtherFast 10/100 5-port Workgroup Switch." Same result.

I then tried using both the hub and the switch:

         ADSL      10 Mb/s  --> Computer A
 DSL --> Modem --> Ethernet
                   Hub      --> Ethernet --> Computer_B
                                Switch          |
                                         --> Computer_C

Again, no change. This time I checked and confirmed that packets were arriving at A at the correct rate for them to be the multicast packets from C.

Unfortunately neither of the switches you tested with had the horsepower (i.e. were managed switches) to control the multicast traffic, though they will segment the unicast traffic. A managed switch (capable of IGMP snooping) would handle the multicast traffic also and eliminate the swamping of machine A.

Do you know if your ADSL modem is doing routing? I would guess it is, and likely is ignoring the multicast traffic as it probably can't (and shouldn't) route it to the Internet at large, but I'd check this to make sure. (It's likely OK, though.) I am curious about this because the IP addresses you have DHCP'd to your machines from the ADSL modem are in the private range. So there is network address translation going on somewhere. How configurable is that ADSL modem?

I can use the 100 Mb/s direct line for many purposes. I can ping over it in either direction; I can ssh into Linux from Windows; I can use Cygwin/X (as described above) to display Linux X programs on the Windows screen.

However, I cannot seem to persuade Windows 2000 Pro to accept multicast packets over the direct line. When I run Linrad on computer C and MAP65 on B, the multicast traffic is always received over the slow line, through the Hub. This uses most of the 10 Mb/s link's bandwidth, and my wife can't read her email when I'm on the air. This is NOT GOOD.

Have you set the multicast boundaries on the W2K box? Do you have the Microsoft w2k Resource Kit installed on the W2k box?

It sounds like the w2k box isn't routing the multicast traffic correctly to the direct interface, instead using the interface to the hub. Or am I misunderstanding in that the direct interface is never used for multicast traffic when 2 interfaces are connected to a machine?reserved local

If I unplug the crossover cable from the Windows machine and instead plug it into a laptop running Win/XP, the laptop receives the multicast packets without a problem.

But in this case there is but one network interface, only the direct interface, right?

And is the Linux box then routing Internet traffic over this direct interface also to the XP machine? Or is there no Internet access over the direct interface via routing in the Linux box?

What is the current implementation of multicast routing in the Kubuntu kernel you are running? It needs to be compiled in, I don't know if this is the case in the version you are running, and then set up.
(PIM-sparse is probably what you want, opt-in for multicasts.)

The simplest thing to do is to use an IGMP aware managed switch and use one interface per machine, letting the switch sort things out, though this would require purchasing a managed switch. List price is in the hundreds of dollars range for low end managed switches, but these are often available on Ebay for less than a hundred bucks. It might still be worth thinking about if you decide to use multiple machines and need the network flexibility and simplicity. # route add -net netmask dev eth1

One other good thing about most managed switches is that they have all metal cases and are shielded pretty well. If you have a well shielded case on the Ethernet switch and metal PC cases, using shielded CAT5 cable can reduce radiated emissions from the networking components. I have found this to be useful on my own setups.

As for number or ports on a switch, you always seem to wind up using more than you think you will, adding other devices like printers, radios, wireless APs, and multiple machines, so I always advise going higher in port count than you think you'll use right away.

Hopefully some of this will be useful.

Rick Kunath, k9ao

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