146 CHAPTER 16: MULTICAST CONFIGURATION GUIDE
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vlan1to3
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vlan 10
service-type multicast
igmp-snooping enable
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interface Ethernet1/0/1
port link-type hybrid
port hybrid vlan 1 to 2 10 untagged
port hybrid pvid vlan 2
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interface Ethernet1/0/2
port link-type hybrid
port hybrid vlan 1 3 10 untagged
port hybrid pvid vlan 3
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interface Ethernet1/0/10
port link-type hybrid
port hybrid vlan 2 to 3 10 tagged
port hybrid vlan 1 untagged
Precautions ■A port belongs to one multicast VLAN only.
■Only Hybrid ports can be connected with receivers.
■Upon receiving a multicast packet, a router port forwards the packet only to
the member ports in the same VLAN. Therefore, the member ports must
belong to the same multicast VLAN with the router port.
■When assigning a router port to a multicast VLAN, be sure to configure it as a
trunk port, or a hybrid port that sends packets of the multicast VLAN with the
VLAN tag kept; otherwise all the member ports in this multicast VLAN will be
unable to receive multicast packets.
Configuring PIM-SM plus IGMP plus IGMP Snooping
PIM-SM is a type of sparse mode multicast protocol. It uses the “pull mode” for
multicast forwarding, and is suitable for large- and medium-sized networks with
sparsely and widely distributed multicast group members.
The basic implementation of PIM-SM is as follows:
■PIM-SM assumes that hosts need multicast data only if they explicitly express
their interest in the data. PIM-SM builds and maintains rendezvous point trees
(RPT) for multicast traffic delivery. An RPT is rooted at a router in the PIM
domain as the common node referred to as rendezvous point (RP), through
which the multicast data travels along the RPT and reaches the receivers.
■When a receiver is interested in the multicast data addressed to a specific
multicast group, the last-hop router sends a join message to the RP
corresponding to that multicast group. The path along which the message
goes hop by hop to the RP forms a branch of the RPT.
■When a multicast source sends multicast traffic to a multicast group, the
first-hop router encapsulates the first packet in a register message, and sends
the message to the corresponding RP by unicast. The arrival of this message at
the RP triggers the establishment of an SPT rooted at the multicast source.