White Papers

VLT and High Availability
High availability (HA) support on VLT ensures seamless and uninterrupted ow of VLT features during RPM failure (failover).
When RPM failover happens, the new active RPM triggers a new VLT registration to its VLT peer. It ensures that the VLT node with new
active RPM receives all the VLT information from its VLT peer. When the standby RPM performs the check-in and registration function
(with the active RPM), the latter performs a bulk synchronization of all the peer VLT information. The existing CLI conguration
synchronized to the standby RPM ensures that the local VLT congurations are always available at standby RPM as well. The VLT backup
link functionality is also modied to manage the two management interfaces in a dual RPM. A virtual management IP must be congured
on the dual RPM VLT node to maintain uninterrupted VLT backup functionality. For more information, refer to “VLT backup link” section in
the Conguration Notes
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 and Stacking
You cannot enable stacking on switches congured for VLT operation.
If you enable stacking on a Dell Networking switch 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 switch.
VLT IPv6
The following features have been enhanced to support VLT on IPv6.
:
• VLT Sync — Entries learned on the VLT interface are synced on both VLT peers.
• Non-VLT Sync — Entries learned on non-VLT interfaces are synced on both VLT peers.
• Tunneling — Control information is associated with tunnel trac so that the appropriate VLT peer can mirror the ingress port as the
VLT interface rather than pointing to the VLT peer’s VLTi link.
• Statistics and Counters — Statistical and counter information displays IPv6 information when applicable.
• Heartbeat — You can congure an IPv4 or IPv6 address as a backup link destination. You cannot use an IPv4 and an IPv6 address
simultaneously. If you have a dual RPM, congure a virtual IP address(ipv4/ipv6) as backup link.
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.
To change the duration of the congurable timer, use the delay-restore command.
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.
Virtual Link Trunking (VLT)
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