[linrad] Re: Testing MAP65 v0.8

[Rick Kunath <charter.net; k9ao@xxxxxxxxxxxxxxxx>]

Joe Taylor wrote:

> My earlier problem with dropped multicast packets seems to be fixed in 
> MAP65 v0.8.  However, when running the Linrad-MAP65 combination on two 
> separate computers I still have some network-related problems.  Perhaps 
> someone on this list who knows much more than I about networking can help.
>
> My computer network looks like this:
>
>
>         ADSL      10 Mb/s  --> Computer_A
> DSL --> Modem --> Ethernet --> Computer_B
>                   Hub            |
>                            --> Computer_C
>
> Three computers are connected to a 10 Mb/s Ethernet Hub.

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

> 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 and C.
>
> 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 
(/etc/iftab):

http://linux.die.net/man/5/iftab

>  Connections to the Hub are assigned 
> dynamic IP addresses;

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

> 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 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.

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.

> 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 224.0.0.0 netmask 224.0.0.0 dev eth0
>
> 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 224.0.0.0 netmask 224.0.0.0 dev eth1
>
> the multicast data are not received by MAP65 running on the other machine.
>
> 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.

As to W2k the unicast and multicast routes are handled in separate 
tables, check here for more info:

http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/intwork/inaf_mul_hwmc.mspx?mfr=true

Hope some of this is of some use :)

Rick Kunath, k9ao



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