[c-nsp] Multicast MAC address

[Vikas Sharma]

Hi Swaroop / Mayers,

Thanks for the information.

Regards
Vikas Sharma


On 6/29/07, Swaroop Potdar <Swaroop.Potdar at corliant.com> wrote:
>
>  Well then i believe it sums up the story for the original poster.
>
> I took care of the LAN (IGMP Snooping) and you took care of the WAN (PIM
> Snooping).
>
> :-)
>
> ------------------------------
> *From:* Phil Mayers [mailto:p.mayers at imperial.ac.uk]
> *Sent:* Fri 6/29/2007 7:30 AM
> *To:* Swaroop Potdar
> *Cc:* Vikas Sharma; cisco-nsp at puck.nether.net
> *Subject:* RE: [c-nsp] Multicast MAC address
>
>
>
> On Fri, 2007-06-29 at 06:06 -0500, Swaroop Potdar wrote:
> > Most WAN media types are P2P in nature so there is no Multicast to MAC
> > mapping.
>
> Well yes, but since the OP mentioned multicast MAC addresses, it was a
> pretty safe bet to assume he was talking about Ethernet
>
> >
> > Since ethernet is a broadcast and multiple access type media in
> > nature, the multicast to mac address mapping is desired to avoid
> > flooding of traffic to all hosts connected to the media.
> >
> > So when you enable IGMP Snooping on a Layer 2 switch it makes a note
> > of all the IGMP requests and converts them to mac equivalent and
> > stores in the cam table. and also reports the same to the router, then
> > the router forwards the traffic feed to the switch and the traffic
> > reaches to the end destinatiosn which had requested the group, but the
> > destination address is the multicast-mac address when it is sent to
> > the end host, hence not everybody receives the traffic, but only the
> > hosts which sent the igmp join will receive the traffic.
>
> Sure - but in an ethernet-as-wan-link setting, IGMP is not likely to be
> in use, it's more likely to be PIM - and PIM snooping (or set
> multicast=flood) is needed if a layer2 hop exists between the two layer3
> endpoints.
>
> >
>
>