[linux-dvb] Re: MPE MAC broadcast

[Julian Somers <lists@bigpip.com>]

On Sat, Feb 05, 2005 at 10:09:27AM +1100, Hamish Moffatt wrote:
> On Fri, Feb 04, 2005 at 04:44:58PM +0100, Evangelos Stergiou wrote:
> > >Well, either I don't understand, or I wasn't clear with this.
> > >
> > >I transmit IP data with a MPE MAC broadcast enveloppe over satellite.
> > >I cannot receive my IP data on my DVB-S card unless its MAC is 
> > >FF:FF:FF:FF:FF:FF or I put it on promisc mode. I mean "any data", not even 
> > >those having destination IP = my card's unicast IP.
> > >
> > >I am a satellite service provider. Suppose I have a park of a thousand 
> > >receiving sites (which I do have).
> > >My gateway encapsulates my IP data into a MPE MAC broadcast enveloppe 
> > >(much easier than having all my sites configured to the same MAC).
> 
> I don't know anything about DVB data transmission. But your description
> makes perfect sense for Ethernet, for example.
> 
> Each station only receives messages which are addressed to its MAC
> address, or sent to the broadcast address. If you want to listen to all
> traffic, you use promiscuous mode.
> 
> It doesn't matter what the IP address is; the MAC function will discard
> any packets without the correct MAC address before the IP address is
> checked. So packets with your IP address sent to the wrong MAC address
> are not useful.
> 
> I think you need to either correctly set the MAC address for each packet
> you are sending (based on the IP address to which its sending, eg
> through ARP) or send all packets to the broadcast address.

Why not avoid the mac adress issue altogether and use multicast? 

Even for point-to-point traffic, we assign each of our users their own
multicast IP so we don't have to bother with mac addresses at all. 

Julian

> 
> 
> Hamish
> -- 
> Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>
> 
>