Users Guide

● If the primary peer fails, the secondary peer takes the primary role. If the primary peer (with the lower priority) later comes
back online, it is assigned the secondary role (there is no preemption).
● In a VLT domain, the peer network devices must run the same OS10 software version.
NOTE: A temporary exception is allowed during the upgrade process. See the Dell EMC SmartFabric OS 10.5.0.x
Release Notes for more information.
● Configure the same VLT domain ID on peer devices. If a VLT domain ID mismatch occurs on VLT peers, the VLTi does not
activate.
● In a VLT domain, VLT peers support connections to network devices that connect to only one peer.
● When you configure a VLT domain, the system generates a VLT Unit-ID. You cannot change the VLT Unit-ID. To identify the
VLT node in a VLT domain, use the show vlt command.
VLT interconnect
A VLT interconnect (VLTi) synchronizes states between VLT peers. OS10 automatically adds VLTi ports to VLANs spanned
across VLT peers, but 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.
● Port-channel 1000 is reserved for the VLTi link and 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 learnt over VLANs on VLT peer nodes synchronize using the VLTi.
● 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.
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 that
are connected at the other end of the VLT port channel interfaces could take a considerable amount of time to detect the
interface status change and switch the traffic towards the other active VLT node. Using LACP PDUs, the graceful LACP feature
enables VLT nodes to inform ToR devices ahead of taking down the member ports of its VLT port channel interfaces. Thus, the
graceful LACP feature 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:
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Virtual Link Trunking