Dell S4820T, Configuration Manual

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VLT Port Delayed Restoration
When a VLT node boots up, if the VLT ports have been previously saved in the start-up configuration,
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 traffic.
The
delay-restore
feature waits for all saved configurations to be applied, then starts a configurable
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 configurable 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.
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.
PIM-Sparse Mode Support on VLT
The designated router functionality of the PIM Sparse-Mode multicast protocol is supported on VLT peer
switches for multicast sources and receivers that are connected to VLT ports.
VLT peer switches can act as a last-hop router for IGMP receivers and as a first-hop router for multicast
sources.
Virtual Link Trunking (VLT)
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