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.
• Congure 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 congure 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 congured on only one peer.
• VLAN ID 4094 is reserved as an internal control VLAN for the VLT domain, and it is not user congurable.
• Port-channel 1000 is reserved for the VLTi link and is not user congurable.
• The VLTi synchronizes L2 and L3 control-plane information across the two nodes. The VLTi is used for data trac only when there is a
link failure that requires VLTi to reach the nal destination.
• Trac with an unknown destination MAC address, multicast, or broadcast trac can cause ooding across the VLTi.
• MAC, ARP, IPv6 neighbors that are learnt over VLANs on VLT peer nodes synchronize using the VLTi.
• LLDP, ow 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 trac 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 trac 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 ows through the optimal path to its destination:
Virtual Link Trunking
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