Re: IP layer and layer 2 IGMP Snooping
- From: Albert Manfredi <bert22306@xxxxxxxxxxx>
- Date: Sun, 8 Jun 2008 09:57:39 -0700 (PDT)
On Jun 7, 1:28 am, vicky <vikrant.pan...@xxxxxxxxx> wrote:
What is the difference in
IP Layer IGMP Snooping and,
Layer 2 IGMP Snooping.
Wait, I think I know what this is referring to.
When doing IGMP snooping, the L2 switch can use the IP address of the
IGMP join messages to derive the MAC multicast address, then use the
MAC multicast address of the arriving data frames to make forwarding
decisions. This is the more "classic" approach. Or the L2 switch can
use the IP address of the arriving UDP/IP datagrams to make the
forwarding decision, and never bother using the MAC multicast address
at all.
Perhaps this is what the terminology is referring to. Using the IP
address to make forwarding decisions is actually preferable, because
28 bits of an IPv4 multicast address determine the multicast group.
When mapped to the MAC address, only 23 bits are used to differentiate
IPv4 multicast groups at the MAC layer, so there is some ambiguity as
to what MAC hosts really want the multicast.
Bert
.
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