Rick, and all --
OK, I've a chance to make some more tests.
My computer network looks like this:
ADSL 10 Mb/s --> Computer_A
DSL --> Modem --> Ethernet --> Computer_B
Three computers are connected to a 10 Mb/s Ethernet Hub.
Additional information: "ipconfig" on Windows, "ifconfig" on Linux,
report the following IP addresses:
Computer A: 172.16.28.67
Computer B(1): 172.16.28.69
Computer B(2): 192.168.10.13
Computer C(1): 172.16.28.31
Computer C(2): 192.168.10.12
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."
I then tried using both the hub and the switch:
ADSL 10 Mb/s --> Computer A
DSL --> Modem --> Ethernet
Hub --> Ethernet --> Computer_B
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
Computer_A is my XYL's machine. Computer_B runs Windows 2000 Pro, and
Computer_C runs Linux (presently the Kubuntu 6.06 distribution). In
addition to the connections of all three machines to the hub, a
crossover cable makes a direct 100 Mb/s connection between computers B
The ethernet interfaces on B and C appear to be configured correctly.
On Linux they appear as eth0 and eth1 (occasionally they boot up as
eth0 and eth2, I don't know why???).
This is configurable, generally, and should be fixed if you intend to
use interface based static routes. Check here for more info on iftab
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 192.168.10.12 and 192.168.10.13 for
the direct inter-machine connection
between B and C.
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
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.
An Ethernet switch would eliminate this, as traffic passing between two
machines (B-C) does not use any bandwidth, nor is it seen, by any other
machines. Internet access by machine A would be unaffected by a transfer
occurring between machines B and C. Machine A would not see the traffic,
nor would there be any contention for bandwidth on it's connection
because of the B-C traffic.
Well, as far as I can see this does not seem to be the case. Can it be
that your statement is true for normal one-to-one IP traffic, but not
for multicast traffic? Or is it true for a router, but not for a switch?
By default the multicast traffic generated by Computer_C goes to
eth0. I can use the Linux "route" command to explicitly tell the
system to use eth0:
# route add -net 18.104.22.168 netmask 22.214.171.124 dev eth0
This works fine (but of course, still sends the heavy multicast
traffic through the hub). If I remove this routing instruction and
# route add -net 126.96.36.199 netmask 188.8.131.52 dev eth1
the multicast data are not received by MAP65 running on the other
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.
Thus, it would seem that the problem must be in my setup of the Win2k
machine -- the one with two ethernet interfaces. Can anyone shed any
light on this situation for me?
Would there be sufficient bandwidth in a 100baseTx connection (100 Mbps
full-duplex) to handle both of the networking streams, i.e. the hub and
the direct stream? If so, replacing the inefficient hub with a faster
switch, thus confining network traffic to only the ports of the involved
machines, might solve the issue. This might allow you to eliminate the
direct connection between machines B and C.
Yes, this would be fine ... if it worked. So far, I have not been able
to make it work.
Anyway, the direct line between B and C should work, no? Why can't I
persuade B to receive multicast packets from C on the direct line??
-- 73, Joe, K1JT
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