Concept Guide

VLT and Stacking
You cannot enable stacking with VLT.
If you enable stacking on a unit on which you want to enable VLT, you must rst remove the unit from the existing stack. After you remove
the unit, you can congure VLT on the unit.
VLT and IGMP Snooping
When conguring IGMP Snooping with VLT, ensure the congurations on both sides of the VLT trunk are identical to get the same
behavior on both sides of the trunk.
When you congure IGMP snooping on a VLT node, the dynamically learned groups and multicast router ports are automatically learned on
the VLT peer node.
VLT Port Delayed Restoration
When a VLT node boots up, if the VLT ports have been previously saved in the start-up conguration, they are not immediately enabled.
To ensure MAC and ARP entries from the VLT per node are downloaded to the newly enabled VLT node, the system allows time for the
VLT ports on the new node to be enabled and begin receiving trac.
The delay-restore feature waits for all saved congurations to be applied, then starts a congurable timer. After the timer expires, the
VLT ports are enabled one-by-one in a controlled manner. The delay between bringing up each VLT port-channel is proportional to the
number of physical members in the port-channel. The default is 90 seconds.
If you enable IGMP snooping, IGMP queries are also sent out on the VLT ports at this time allowing any receivers to respond to the queries
and update the multicast table on the new node.
This delay in bringing up the VLT ports also applies when the VLTi link recovers from a failure that caused the VLT ports on the secondary
VLT peer node to be disabled.
VLT Routing
VLT routing is supported on the Aggregator.
Layer 2 protocols from the ToR to the server are intra-rack and inter-rack. No spanning tree is required, but interoperability with spanning
trees at the aggregation layer is supported. Communication 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 congured 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.
Non-VLT ARP Sync
In the Dell Networking OS version 9.2(0.0), ARP entries (including ND entries) learned on other ports are synced with the VLT peer to
support station move scenarios.
Prior to Dell Networking OS version 9.2.(0.0), only ARP entries learned on VLT ports were synced between peers.
PMUX Mode of the IO Aggregator
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