A triangle design is an SMLT configuration that connects edge switches or SMLT clients to two aggregation switches. Connect the aggregation switches together with a vIST that carries all the SMLT trunks configured on the switches.
The switch supports the following triangle configurations:
a configuration with Layer 3 PIM-SM routing on both the edge and aggregation switches
a configuration with Layer 2 snooping on the client switches and Layer 3 routing with PIM-SM on the aggregation switches
To avoid using an external query device to provide correct handling and routing of multicast traffic to the rest of the network, use the triangle design with IGMP Snoop at the client switches. Use multicast routing at the aggregation switches as shown in the following figure.
Client switches run IGMP Snoop or PIM-SM, and the aggregation switches run PIM-SM. This design is simple and, for the rest of the network, PIM-SM performs IP multicast routing. The aggregation switches are the query devices for IGMP, so an external query device is not required to activate IGMP membership. These switches also act as redundant switches for IP multicast.
Multicast data flows through the vIST link when receivers are learned on the client switch and senders are located on the aggregation switches, or when sourced data comes through the aggregation switches. This data is destined for potential receivers attached to the other side of the vIST. The data does not reach the client switches through the two aggregation switches because only the originating switch forwards the data to the client switch receivers.
Note
Always place multicast receivers and senders on the core switches on VLANs different from those that span the vIST.
The following figure shows a switch clustering configuration with a single switch cluster core and dual-connected edge devices. This topology represents different VLANs spanning from each edge device and those VLANs routed at the switch cluster core. You can configure multiple VLANs on the edge devices, 802.1Q tagged to the switch cluster core.
Use an edge device that supports a form of link aggregation. Disable spanning tree on the link aggregation group on the edge devices. Enable either Virtual Router Redundancy Protocol (VRRP) BackupMaster or Routed SMLT (RSMLT) Layer 2 Edge on the switch cluster core.