Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 1000

Each VLT peer runs its own PIM protocol independently of other VLT peers. To ensure the PIM protocol states or multicast routing information base (MRIB) on the VLT peers are synced, if the incoming interface (IIF) and outgoing interface (OIF) are Spanned, the multicast route table is synced between the VLT peers. To verify the PIM neighbors on the VLT VLAN and on the multicast port, use the show ip pim neighbor, show ip igmp snooping mrouter, and show running config commands. You can configure virtual link trunking (VLT) peer nodes as rendezvous points (RPs) in a Protocol Independent Multicast (PIM) domain. If the VLT node elected as the designated router fails and you enable VLT Multicast Routing, multicast routes are synced to the other peer for traffic forwarding to ensure minimal traffic loss. If you did not enable VLT Multicast Routing, traffic loss occurs until the other VLT peer is selected as the DR. VLT Routing VLT Routing refers to the ability to run a dynamic routing protocol within a single VLT domain or between VLT domains (mVLT). In a single VLT domain, VLT routing allows routing adjacencies to be formed across the VLTi link. In eVLT, routing adjacencies are formed across the port-channel that connects the two VLT domains. Because VLT ports are Layer 2 ports and not IP interfaces, VLT Unicast and VLT Multicast routing protocols do not operate directly on VLT ports. You must add the VLT ports as a member of one or more VLANs and assign IP addresses to these VLANs. VLT Unicast and VLT Multicast routing protocols require VLAN IP interfaces for operation. Protocols such as BGP, ISIS, OSPF, and PIM are compatible with VLT Unicast Routing and VLT Multicast Routing. Layer 2 protocols from the ToR devices to the server are intra-rack and inter-rack. Although no spanning tree is required, interoperability with spanning trees at the aggregation layer is supported to prevent switching loops from forming due to any incorrect configuration. . Communication between devices is active-active, with no blocked links. MAC tables are synchronized between VLT nodes for bridging and you can enable IGMP snooping. Spanned VLANs Any VLAN configured on both VLT peer nodes is referred to as a Spanned VLAN. The VLT Interconnect (VLTi) port is automatically added as a member of the Spanned VLAN. As a result, any adjacent router connected to at least one VLT node on a Spanned VLAN subnet is directly reachable from both VLT peer nodes at the routing level. Peer Routing Peer routing enables one VLT node to act as a proxy gateway for the other peer in a VLT domain. When you enable routing on VLT peers, you can also enable the peer routing feature. The following figure shows how a packet is routed when peer routing is not enabled. Due to the hashing algorithm in the port channel, a packet from a host is sent to either of the VLT port-channel members. If a packet is sent to Peer-1 which is not the destined gateway for the hosts under the ToR Switch, the packet is switched to the destined VLT peer (Peer-2) using the VLTi link. Peer-2 then routes the packet to its destination. 1000 Virtual Link Trunking (VLT)