Dell Force10 Part 3: VLT Domain Configuration

dell-force10In my previous post here I went through VLT basics and how it helps to establish a loop-free network topology in a modern datacenter. Now lets dive deeper and see how VLT is configured from FTOS CLI.

VLT Configuration

The first step is to configure the backup links and VLT interconnect. Dell S4048-ON switches have six 40Gb QSFP+ ports, two of which 1/49 and 1/50 we will use for VLTi. Repeat the same configuration on both switches.

# int range fo 1/49-1/50
# no shutdown

# interface port-channel 127
# description “VLT interconnect”
# channel-member fo 1/49
# channel-member fo 1/50
# no shutdown

Now that we have a VLT interconnect set up, let’s join the first switch to a VLT domain:

# vlt domain 1
# back-up destination
# peer-link port-channel 127
# primary-priority 1

First switch points to the second switch management IP for a backup destination, uses port channel 127 as a VLT interconnect and becomes a primary peer, because it’s given the lowest priority of 1.

Do the same on the second switch, but now point to the first switch management IP for backup and use the highest priority to make this switch a secondary peer:

# vlt domain 1
# back-up destination
# peer-link port-channel 127
# primary-priority 8192

To confirm the VLT state use the following command:

# sh vlt brief


As you can see, the VLTi and backup links are up and the switch can see its peer. For some additional VLT specific information use these commands:

# sh vlt statistics
# sh vlt backup-link

I would also recommend to use the following command to see the port channel state and confirm that both VLTi links are in up state:

# sh int po127



In this part of the Dell Force10 switch configuration series we quickly went through the initial VLT setup. We haven’t touched on VLT LAG configuration yet. We will take a closer look at it in the next blog post.


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2 Responses to “Dell Force10 Part 3: VLT Domain Configuration”

  1. UBE Says:

    DELL recommends in their Reference Architecture to configure a manually a virtual MAC-Address for the VLT-Domain (Document found here:

    • niktips Says:

      This is a very good point. There are a number of recommended parameters that can make your configuration more deterministic and improve convergence, this includes RSTP tuning, port dampening and VLT system parameters. In this series I tried to explain the basics. For some of the additional optimization I encourage everyone to read the “VLT Technical Guide” by Dell Force10.

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