Owner's Manual

752 | Chapter 27. Multicast Routing and Switching
NETGEAR 8800 User Manual
Figure 90. Multiple VLANs in the Core Network
In Figure 90, the core network has 2 more VLANs, vc1 and vc2, to provide other services.
With MVR, multicast traffic should be confined to McastVlan, and should not be forwarded to
vc1 and vc2. Note that MVR is configured only on the ingress VLAN (McastVlan). MVR is not
configured on any other VLANs.
In the same way as the IGMP snooping forwarding rules, the multicast stream is forwarded
onto member ports and router ports on the VLAN. For a stream received on MVR enabled
ports, this rule is extended to extend membership and router ports to all other VLANs. This
rule works well on the topology in
Figure 89. However, in a tagged core topology, this rule
forwards traffic onto VLANs, such as vc1 and vc2, on ports PC1 and PC2. This results in
multiple copies of same stream on the core network, thus reintroducing the problem that
MVR was intended to solve.
To avoid multiple copies of the same stream, MVR forwards traffic with some special
restrictions. MVR traffic is not forwarded to another VLAN unless a host is detected on the
port. On the ingress MVR VLAN, packets are not duplicated to ports belonging to MVR
VLANs. This is to prevent duplicate multicast traffic streams on ingress ports. Streams
belonging to static MVR groups are always forwarded on MVR VLANs so that any host can
join such channels immediately. However, dynamic groups are streamed from the server only
if some host is interested in them. A command is provided to receive traffic on a port which is
excluded by MVR. However, regular IGMP rules still apply to these ports, so the ports must
have a router connected or an IGMP host to receive the stream.
These rules are to prevent multicast packets from leaking into an undesired virtual port, such
as p2 on VLAN pc2 in
Figure 90. These rules also allow that, in most topologies, MVR can
be deployed with minimal configuration. However, unlike STP, MVR is not intended to be a
Layer
2 protocol to solve packet looping problems. Since multicast packets leak across
VLANs, one can misconfigure and end up with a multicast storm. MVR does not attempt to
solve such problems.
EX_144
Switch1
Vlan2 vc2
PC2PC1
p1
p2
H2 H4
McastVlan, vc1, vc2
McastVlan, vc1, vc2
H3
H3