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Understanding Multicast VLAN Registration on EX Series Switches
Multicast VLAN registration (MVR) allows you to efficiently distribute IPTV multicast streams across an Ethernet ring-based Layer 2 network and reduce the amount of bandwidth consumed by this multicast traffic.
In a standard Layer 2 network, a multicast stream received on one VLAN is never distributed to interfaces outside that VLAN. If hosts in multiple VLANs request the same multicast stream, a separate copy of that multicast stream is distributed to the requesting VLANs.
MVR introduces the concept of a multicast source VLAN (MVLAN), which is created by MVR and becomes the only VLAN over which IPTV multicast traffic flows throughout the Layer 2 network. The Juniper Networks EX Series Ethernet Switch that is enabled for MVR selectively forward IPTV multicast traffic from interfaces on the MVLAN (source interfaces) to hosts that are connected to interfaces that are not part of the MVLAN. These interfaces are known as MVR receiver ports. The MVR receiver ports can receive traffic from a port on the MVLAN but cannot send traffic onto the MVLAN, and they remain in their own VLANs for bandwidth and security reasons.
This topic includes:
How MVR Works
In many ways, MVR is similar to IGMP snooping. Both monitor IGMP join and leave messages and build forwarding tables based on the media access control (MAC) addresses of the hosts sending those IGMP messages. Whereas IGMP snooping operates within a given VLAN to regulate multicast traffic, MVR can operate with hosts on different VLANs in a Layer 2 network to selectively deliver IPTV multicast traffic to requesting hosts, thereby reducing the amount of bandwidth needed to forward multicast traffic.
When you configure an MVLAN, you assign a range of multicast group addresses to it. You then configure other VLANs to be MVR receiver VLANs, which receive multicast streams from the MVLAN. The MVR receiver ports comprise all the interfaces that exist on any of the MVR receiver VLANs. Interfaces that are on the MVLAN itself cannot be MVR receiver ports for that MVLAN.
 | Note: MVR is supported on VLANs running IGMP version 2 (IGMPv2) only. |
MVR Modes
MVR operates in two modes: MVR transparent mode and MVR proxy mode. Both modes allow MVR to forward only one copy of a multicast stream to the Layer 2 network.
MVR Transparent Mode
In MVR transparent mode (the default mode), the switch receives one copy of each IPTV multicast stream and then replicates the stream only to those hosts that want to receive it, while forwarding all other types of multicast traffic without modification. Transparent mode is the default mode.
The switch handles IGMP packets destined for both the multicast source VLAN and multicast receiver VLANs in the same way that it handles them when MVR is not being used. That is, when a host on a VLAN sends IGMP join and leave messages, the switch floods the messages to all router interfaces in the VLAN. Similarly, when a VLAN receives IGMP queries from its router interfaces, it floods the queries to all interfaces in the VLAN.
If a host on a multicast receiver port joins an MVR group on the multicast receiver VLAN, the appropriate bridging entry is added and the MVLAN forwards that group’s IPTV multicast traffic on that port (even though that port is not in the MVLAN). Likewise, if a host on a multicast receiver port leaves an MVR group on the multicast receiver VLAN, the appropriate bridging entry is deleted and the MVLAN stops forwarding that group’s IPTV multicast traffic on that port. In addition, you can configure the switch to statically install the bridging entries on the multicast receiver VLAN.
MVR Proxy Mode
When you use MVR in proxy mode, the switch acts as a proxy for any MVR group in both the upstream and downstream directions. In the downstream direction, the switch acts as the querier for the groups in the MVR receiver VLANs. In the upstream direction, the switch originates the IGMP reports and leaves and answers IGMP queries from multicast routers. When the MVR receiver VLANs receive IGMP joins and leaves, the switch creates bridging entries on the MVLAN as needed, as it does in MVR transparent mode. In addition, the switch sends out IGMP joins and leaves on the MVLAN based on these bridging entries.
Configuring MVR proxy mode on the MVLAN automatically enables IGMP snooping proxy mode on all MVR receiver VLANs as well as on the MVLAN.
