Re: UDP Broadcast

Hi.

Patrick Klos schrieb:
In article <e4s3ff$8lh$1@xxxxxxxxxxxxxxxxx>,
Michael Wuest <michael.wuest@xxxxxxxxxxxx> wrote:

Hi @ all,

I have the following problem:

System is Debian Linux Sarge with Kernel 2.4.29. I want to
send and receive UDP Broadcasts. I have no firewall
installed, the system is very basic.

The Broadcasts need to be received from systems not being
in the same subnet and to be sent to systems not being in
the same subnet.

I am using sockets with SO_BROADCAST enabled. The packet
is sent out and received, but only in the same subnet, not
in other subnets being on the same physical network.


By saying you have several subnets, you imply there is a router between
these subnets. Generally, IP broadcasts are not propagated through routers
unless the router is specifically set up to forward such broadcasts.

AFAIK broadcasts are possible to all systems on your physical
network through "255.255.255.255". In fact I do not want to route
anything since I do not know what the subnet is I want to adress.

The application is an configuration program for a linux machine
to set up ip adresses. To achieve this task I need to reach the
target machine if it is available and to ask the machine of its
current ip adress regardless if it fits into my TCP/IP subnet
or not.



What am I doing wrong? What is exactly the meaning of the
broadcast value in /etc/network/interfaces? Are there any
specific parameters to be set? Are there any special kernel
issues that need recompiling? Is the broadcast adress
255.255.255.255 correct?


Again, it's not that you are necessarily doing anything wrong in your Linux
box - it's more that the router between your machine and the target subnet
does not forward broadcasts. (unless your Linux box IS the router between
the subnets in question??)

To be more clearly, I want the linux machine to "forward" the
broadcast being sent to "255.255.255.255" to all subnets being
available on my physical network.



Maybe someone has any for functionality approved command
line test program that sends out any "text" by UDP broadcast
so that I can check whether the linux is blocking or my
configuration is or my programing is wrong.

Any help appricated. Links to FAQs, PDFs appreciated too.


Not a definitive answer, but I hope I helped shed some light on the
situation? If not, describe the subnets and routers involved please?

Patrick
========= For LAN/WAN Protocol Analysis, check out PacketView Pro! =========
Patrick Klos Email: patrick@xxxxxxxx
Klos Technologies, Inc. Web: http://www.klos.com/
==================== http://www.loving-long-island.com/ ====================

Bye,
Michael.

.

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