Multicast Packet Forwarding Mechanism; Multi-Instance Multicast - HP A6600 Configuration Manual

Multicast VLAN/IPv6 multicast VLAN
In the traditional multicast on-demand mode, when users in different VLANs on a Layer 2 device need
multicast information, the upstream Layer 3 device needs to forward a separate copy of the multicast data
to each VLAN of the Layer 2 device. When the multicast VLAN or IPv6 multicast VLAN feature is enabled
on the Layer 2 device, the Layer 3 multicast device sends only one copy of the multicast data to the
multicast VLAN or IPv6 multicast VLAN on the Layer 2 device. This approach avoids waste of network
bandwidth and extra burden on the Layer 3 device.

Multicast packet forwarding mechanism

In a multicast model, a multicast source sends information to the host group identified by the multicast
group address in the destination address field of IP multicast packets. To deliver multicast packets to
receivers located in different parts of the network, multicast routers on the forwarding path usually need to
forward multicast packets received on one incoming interface to multiple outgoing interfaces.
Compared with a unicast model, a multicast model is more complex in the following aspects:
To ensure multicast packet transmission in the network, unicast routing tables or multicast routing
•
tables (for example, MBGP routing table) specially provided for multicast must be used as guidance
for multicast forwarding.
• To process the same multicast information from different peers received on different interfaces of the
same device, every multicast packet undergoes an RPF analysis on the incoming interface. The RPF
analysis determines whether the packet is forwarded or discarded. The RPF analysis mechanism is
the basis for most multicast routing protocols to implement multicast forwarding.
For more information about the RPF mechanism, see IP Multicast Configuration Guide.

Multi-instance multicast

Multi-instance multicast refers to multicast in a VPN. VPN networks must be isolated from one another and
from the public network.
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