In a Layer 2 ring topology, MVR works with STP as it works with EAPS (Extreme Automatic Protection Switching). However, in other Layer 2 topologies, additional configuration steps may be needed to make sure that multicast feeds reach all network segments. Extra configuration is required because all ports in the VLAN (Virtual LAN) are part of an STP (Spanning Tree Protocol) domain, so that solely by examining the configuration it is not clear whether a port is part of bigger ring or is just serving a few hosts. In EAPS this problem is solved by distinguishing between configured primary or secondary ports from other VLAN ports. Consider a simplified Layer 2 STP network as shown in MVR with STP.
In this topology, subscribers are in a Layer 2 cloud on VLAN V1.
STP is configured for all ports of V1. Since V1 spans on the ring as well, multicast cannot be forwarded on V1 blindly. Forwarding rules (described in MVR Forwarding), dictate that multicast traffic is not forwarded on STP enabled ports. This is to make sure that multiple copies of multicast packets are not forwarded on the ring. However, since other STP enabled ports on V1 (1:3,1:4) are not part of the ring multicast stream, they need to be configured so that they get the packets. To configure the ports to receive packets, use the following command (mentioned in MVR Forwarding):
configure mvr vlan vlan-name add receiver port port-list
Note
If the Layer 2 cloud is connected back to ring ports, traffic may end up leaking into VLAN V1 in the ring. There is no way to avoid that. So, such topologies must be avoided.The following is a typical configuration for Switch 1:
create vlan v1 configure v1 tag 200 configure v1 add port 1:1, 1:2 tag configure v1 add port 1:3, 1:4 create vlan mvlan configure mvlan add port 1:1, 1:2 configure mvr add vlan mvlan create stpd stp1 configure stp1 add vlan v1 port all enable stpd stp1 port all configure mvr vlan v1 add receiver port 1:3,1:4 enable mvr
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