Reference Guide

1010 | Virtual Link Trunking (VLT)
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• 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 JumpStart mode, it will not be able to reach the DHCP server, resulting in BMP
failure.
Configuration Notes
When you configure VLT, the following conditions apply:
• VLT domain
• A VLT domain supports two chassis members, which appear as a single logical device to network
access devices connected to VLT ports through a port channel.
• A VLT domain consists of the two core chassis, the interconnect trunk, backup link, and the LAG
members connected to attached devices.
• Each VLT domain has a a unique MAC address that is created automatically by VLT or
user-configured.
• ARP tables are synchronized between the VLT peer nodes.
• VLT peer switches operate as separate chassis with independent control and data planes for
devices attached on non-VLT ports.
• One chassis in the VLT domain is assigned a primary role; the other chassis takes the secondary
role. The primary and secondary roles are required for scenarios when connectivity between the
chassis is lost. VLT assigns the primary chassis role according to the lowest MAC address. The
primary role is also user-configurable.
• In a VLT domain, the peer switches must run the same FTOS software version
• You must separately configure each VLT peer switch with the same VLT domain ID and the VLT
version. If the system detects mismatches between VLT peer switches in the VLT domain ID or
VLT version, the VLT Interconnect (VLTi) will not activate. To find the reason for the VLTi
being down, use the
show vlt statistics command to verify there are mismatch errors, then use the
show vlt brief command on each VLT peer to view the VLT version on the peer switch. If the VLT
version is more than one release different from the current version in use, the VLTi will not
activate.
• The chassis members in a VLT domain support connection to orphan hosts and switches that are
not connected to both switches in the VLT core.
• VLT interconnect (VLTi)
• The VLT interconnect must consist of either 10G or 40G ports. A maximum of eight 10G or four
40G ports is supported. A combination of 10G and 40G ports is not supported.
• A VLT interconnect over 1G ports is
not supported.
• The port channel must be in default mode (not switchport) to be recognized by VLTi.
• The system will automatically include required VLANs in VLTi. You do not need to manually
select VLANs.
• VLT peer switches operate as separate chassis with independent control and data planes for
devices attached on non-VLT ports.
• Port-channel link aggregation (LAG) across the ports in the VLT interconnect is required;
individual ports are not supported. Dell Force10 strongly recommends configuring a static LAG
for VLTi.
• The VLT interconnect synchronizes L2 and L3 control-plane information across the two chassis.