Netgear XCM8806 Chassis User Manual - Page 752

NETGEAR 8800 User Manual McastVlan, vc1, vc2 PC1 Vlan2 p1 McastVlan, vc1, vc2 PC2 Switch1 p2 vc2 H2 H3 H4 EX_144 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. 752 | Chapter 27. Multicast Routing and Switching