begin Wednesday 14 January 2004 15:45, VOET Emmanuel quote:
I am very glad to have found such a tool.
For the recursive organisation of a course,
I have to replicate a source disk image to the 10 student's disks.
So UDPcast is the tool I was looking to.
I've downloaded the CD image and tested it successfully through a
crosscable (100Mbps=>90Mbps), through a hub (10Mbps=>8MBps), and through
the switch (100Mbps=>89Mbps) when only one receiver. Then I tried to add a
second receiver and ... the flow rate fell from 89Mbps to ... 1,7Mbps
Aaargh. Could someone help me in discovering why and how to solve this ?
You have probably some very slow device connected (directly or
indirectly) to the switch, and as soon as udpcast goes into multicast
mode (which happens if there are more than one receiver), the switch
tries to slow down the communication enough that "everybody" can
However, the problem is that most switches really do mean "everybody",
and not only those nodes that actually participate in the udpcast
transmission. Chances are, however, that the slow device is some old
network printer forgotten in some corner, an old Dos machine, or sth
of that ilk... Remember: the device does not need to be directly
connected to the switch that you are using: it can be several hops
away. Switches are capable of propagating flow control to each other.
There are serveral ways to address this.
1. If your switch supports it, try enabling IGMP-snooping. This makes
the switch aware which node is, and which node isn't interested in
the udpcast transmission.
2. If you have no IGMP snopping, or if it doesn't work (such as on
some 3com switches...), try switching off flow control.
3. If switching off flow control doesn't help either, try
disconnecting all devices from the switch which don't participate in
the udpcast. Disconnect them one by one to find out which one of them
is causing the hold up.
I would also adapt the CD image so all parameters are
defined, and one CD
would be the "sender" CD, and the 10 others the "receiver" CDs.
someone tell me how to do that ?
For the moment, you have to do this manually, by including an
approprate udpcfg.txt into the CD image. Details are described at the
Config file syntax is described at the following URL:
Here is one sample udpcfg.txt file that you might use on the receiver:
For the sender, just replace umode=rcv with umode=snd
I've planned to enhance the online configuration tool
(udpcast.linux.lu/cast-o-matic) to do such things online, the new
version will probably be ready early in February.