Re: When does Linux drop UDP packets?

From: david
Date: Fri Jun 05 2009 - 15:15:53 EST


On Fri, 5 Jun 2009, Alexander Clouter wrote:

Hi,

* david@xxxxxxx <david@xxxxxxx> [2009-06-04 16:19:56-0700]:

On Thu, 4 Jun 2009, Alexander Clouter wrote:

Philipp Reh <sefi@xxxxxxxxxx> wrote:

I have the following setting in which a client that resides on the same
physical network as a server wants to receive any UDP packet that
arrives on any of its interfaces sent by that server.

Read up about multicasting, it will do what you want, does not depend on
the IP address of the destination workstation and will also cross
subnets if you want it to.

It's dead easy to transmit and receive multicast traffic, broadcasting
network traffic is so 1980's :)

there is only a difference between multicast and broadcast traffic if you
are spanning subnets.

Well yes and no. Broadcast traffic is *always* handled by the kernel as
only the kernel can tell if it is interested in it or not. With
multicast the NIC is configured to only pass particular
Ethernet multicast packets up to the kernel.

By using broadcast traffic the load (okay, hardly a big problem
now-a-days) hits *all* the workstations on the subnet, with multicast,
only those interested in the traffic receive it.

true, but only for some NICs, and even those tend to have a fairly small number of slots for the filters. past these limits the OS handles it all just like broadcasts.

David Lang
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