The VLT-Fabric Manager (VLT- FM) module implements the core VLT protocol functionalities and VLT fabric orchestration. Other modules in the system use the services of VLT-FM to achieve the complete VLT solution.
The VLT fabric consists of two nodes providing a logical single switch view to the connected devices. However, each of the VLT peers maintains separate control and data planes and can be configured individually for a port, protocol, and management behaviors.
The VLT design architecture is based on the VLT fabric manager process, controlling the VLT neighbor, and overall fabric orchestration. The protocol used to communicate between VLT peers is defined as VLT Control Protocol (VLT-CP). The Node Discovery Service module, or NDS, handles the topology discovery and management. On receiving the topology update message, VLT-FM builds raw topology and initiates a loop-prevention algorithm to construct the overlay topology.
The VLT application elects the primary node that is based on the lower MAC address; however, with the primary-priority command, the node with the least primary priority becomes the primary node. This election is not preempted, which means that the primary role does not change until the nodes are rebooted or the VLT process is restarted whenever there is a change in priority.
A VLT interconnect (VLTi) synchronizes states between VLT peers. Dell EMC SmartFabric OS10 automatically adds VLTi ports to VLANs spanned across VLT peers, but does not add VLTi ports to VLANs configured on only one peer.
- The VLTi synchronizes Layer 2 and Layer 3 control-plane information across the two nodes. The VLTi is used for data traffic only when there is a link failure that requires VLTi to reach the final destination.
- LLDP, flow control, port monitoring, and jumbo frame features are supported on a VLTi. By default, VLTi ports are set to the maximum supported MTU value.
- MAC, ARP, IPv6 neighbors learned over VLANs on VLT peer nodes synchronize using the VLTi.
The VLT-related information between the nodes is exchanged through the specific reserved VLAN (VLAN 4094). The VLT database (VLT DB) stores the VLT control information exchanged between the VLT nodes. The local database (Local DB) stores the MAC and ARP table entries.
The design and operation of internal communication details and failure handling are beyond the scope of this document.