Configuring Virtual Link Trunking; Important Points To Remember - Dell Force10 S4810P Configuration Manual

VLT domain - This domain includes both VLT peer devices, the VLT interconnect, and all of the port
channels in the VLT connected to the attached devices. It is also associated to the configuration mode that
must be used to assign VLT global parameters.
VLT peer device - One of a pair of devices that are connected with the special port channel known as the
VLT interconnect (VLTi).

Configuring Virtual Link Trunking

VLT requires that you enable the feature and then configure the VLT domain, backup link, and VLT
interconnect on both peer switches.

Important Points to Remember

• VLT port channel interfaces must be switch ports.
• If RSTP is included on the system, it must be configured before VLT. See
• Dell Force10 strongly recommends that the VLTi (VLT interconnect) must be a static LAG and that
LACP should be disabled on the VLTi.
• The spanning tree root bridge should be at the Aggregation layer. If RSTP is enabled on the VLT
device, refer to
• If both VLT peers are rebooted in BMP mode and VLT LAGs are static, the DHCP server reply to the
DHCP discover offer may not be forwarded by the ToR to the correct node. To avoid this scenario,
configure the VLT LAGs to the ToR and the ToR port channel to the VLT peers with LACP. If
supported by the ToR, enable the
member-independent port-channel.
• If the
After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity.
• When IGMP snooping is enabled on the VLT peers, ensure the value of the
not less than the query interval.
• When Layer 3 routing protocols are enabled on VLT peers, make sure the
value that allows sufficient time for all routes to establish adjacency and exchange all the L3 routes
between the VLT peers before the VLT ports are enabled.
• The
lacp ungroup member-independent
using BMP to upgrade or boot from the network.
• Ensure all port channels where LACP ungroup is applicable are configured as hybrid ports and as
untagged members of a VLAN. BMP uses untagged DHCP packets to communicate with the DHCP
server.
• If the DHCP server is located on the ToR and the VLTi (ICL) is down due to a failed link when a VLT
node is rebooted in BMP mode, it will not be able to reach the DHCP server, resulting in BMP failure.
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| Virtual Link Trunking (VLT)
RSTP and VLT
feature is not supported on the ToR, VLT peers should be rebooted one at a time.
lacp-ungroup
for guidelines to avoid traffic loss.
feature on the ToR using the command
lacp-ungroup
command should only be used if the system connects to nodes
RSTP Configuration.
lacp ungroup
command is
delay-restore
timer is set to a
delay-restore