Re: local multicast routing

["Marco P." <marco.tijuana@xxxxxxxxx>]

I think packets are pushed in any case to the network for a simple  
reason: the kernel has no way of knowing that the ONLY receiver in the  
network is on the same machine.
(you can confirm this by sniffing your own traffic with tcpdump/ 
wireshark but i'm pretty sure).

Now, beside that, there may be some 'shortcut' so that receivers on  
the same machine receive the packet without going all the way down to  
the NIC and back.
I also think you can force the multicast to be local by binding to the  
localhost interface instead of the real network card.

Marco

On Feb 17, 2010, at 22:38 PM, Matt Garman wrote:

> Say I have two multicast programs running on the same machine.  One
> is a sending program, and one is a receiving program.  The receiving
> program has joined the group to which the sender in sending.
>
> How does the Linux kernel route these packets?  I.e., are the
> packets just pushed out to the switch for routing, or is the kernel
> smart enough to do some "local delivery" and directly deliver
> packets to the listener?
>
> Thank you,
> Matt
>
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