Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

This feature supports inter-server multicast communication between top-of-rack (ToR) switches using an inter-VLAN Layer 3 routing protocol (for example, PIM, IS-IS, or OSPF). It also provides traffic resiliency during multicast routing convergence after failure without disrupting or altering multicast routing behavior.

Layer 2 protocols from the ToR to the server are intra-rack and inter-rack. No spanning tree is required, but interoperability with spanning trees at the aggregation layer is supported. Communication is active-active, with no blocked links. MAC tables are synchronized between VLT nodes for bridging and IGMP snooping can be enabled.

VLT multicast is also scalable, so additional racks can be implemented in an existing system to provide additional resiliency and resources to accommodate an increased need or to anticipate future growth. You can enable VLT unicast and multicast routing across multiple configurations using VLT links. Protocols such as BGP, OSPF, and PIM are compatible with VLT multicast.

Important Points to Remember

• You cannot configure a VLT node as a rendezvous point (RP), but any PIM-SM compatible VLT node can serve as a designated router (DR).
• You can only use one spanned VLAN from a PIM-enabled VLT node to an external neighboring PIM router.
• If you connect multiple spanned VLANs to a PIM neighbor, or if both spanned and non-spanned VLANs can access the PIM neighbor, ECMP can cause the PIM protocol running on each VLT peer node to choose a different VLAN or IP route to reach the PIM neighbor. This can result in issues with multicast route syncing between peers.
• Both VLT peers require symmetric Layer 2 and Layer 3 configurations on both VLT peers for any spanned VLAN.
• For optimal performance, configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLAN interfaces.
• When using factory default settings on a new switch deployed as a VLT node, packet loss may occur due to the requirement that all ports must be open.
• You can enable ECMP on VLT nodes using VLT unicast; however, ECMP is not compatible on VLT nodes using VLT multicast. You must use a single VLAN.