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  Chapter 14.  MVR (Multicast VLAN Registration)
 
   
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14.   
MVR (Multicast VLAN Registration)
This chapter provides the following examples:
The IGMP Layer 3 protocol is widely used for IPv4 network multicasting. In Layer 2 networks, 
the IGMP protocol uses resources inefficiently.  For example, a Layer 2 switch multicasts 
traffic to all ports even if there are receivers connected to only a few ports.
To fix this problem, the IGMP Snooping protocol was developed.  But the problem reappears 
when receivers are in different VLANs. Multicast VLAN Registration (MVR) is intended to 
solve the problem of receivers in different VLANs.  It uses a dedicated manually configured 
VLAN, called the multicast VLAN, to forward multicast traffic over Layer 2 network in 
conjunction with IGMP snooping.
MVR, like the IGMP Snooping protocol, allows a Layer 2 switch to snoop on the IGMP 
control protocol.  Both protocols operate independently of each other.  Both protocols can be 
enabled on the switch interfaces at the same time.  In such a case, MVR listens to the join 
and report messages only for groups configured statically.  All other groups are managed by 
IGMP snooping.
There are two types of MVR ports: source and receiver.
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The source port is the port to which the multicast traffic flows using the multicast VLAN.  
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The receiver port is the port where a listening host is connected to the switch. It can 
utilize any (or no) VLAN, except the multicast VLAN. This implies that the MVR switch 
performs VLAN tag substitution from the multicast VLAN source port to the VLAN tag 
used by the receiver port.
The Multicast VLAN is the VLAN that is configured in the specific network for MVR purposes.  
It has to be manually specified by the operator for all source ports in the network.  It is a 
VLAN that is used to transfer multicast traffic over the network to avoid duplication of