Dell PowerSwitch S4128F-ON OS10 Enterprise Edition User Guide Release 10.4.3.0 - Page 1036

VLT interconnect A VLT interconnect (VLTi) synchronizes states between VLT peers. OS10 automatically adds VLTi ports to VLANs spanned across VLT peers and does not add VLTi ports to VLANs configured on only one peer. • VLAN ID 4094 is reserved as an internal control VLAN for the VLT domain, and it is not user configurable. • The VLTi synchronizes L2 and L3 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. • Traffic with an unknown destination MAC address, multicast, or broadcast traffic can cause flooding across the VLTi. • MAC, ARP, IPv6 neighbors that are learned over VLANs on VLT peer nodes synchronize using VLTi. • LLDP, flow control, port monitoring, and jumbo frame features are supported on a VLTi. Graceful LACP with VLT When a VLT node is reloaded, all its interfaces including VLT port-channel interfaces go down. Top-of-rack (ToR) devices connected at the other end of the VLT port-channel interfaces take a considerable amount of time to detect the interface status change and switch the traffic towards the other active VLT node. This causes traffic loss for a long time interval. Using LACP PDUs, the graceful LACP feature allows VLT nodes to inform ToR devices ahead of taking down the member ports of its VLT port-channel interfaces. This enables the ToR devices to switch the traffic to the other active VLT node. Graceful LACP is supported in these scenarios: • When a VLT node is reloaded. • When the secondary VLT node detects that the VLTi link is down but the heartbeat is functional. Graceful LACP is enabled by default and you cannot disable it. The following shows the normal behavior of a VLT setup where data flows through the optimal path to its destination. 1036 Virtual Link Trunking