Hello,

in OS10, simply changing the discovery-interface range doesn’t automatically add those interfaces to the VLT port-channel. You’ll still need to manually assign the new interfaces to the port-channel used for the VLT interconnect (usually Port-channel 1000).

@DELL-Erman O​ 

this is not accurate as you can’t manually assign port-channel 1000

sw2(conf-range-eth1/1/49-1/1/52)# channel-group 
  <1-999,1001-2000>  Specify a port channel number

Oops yeah, you’re right. You can’t manually assign interfaces to Port-channel 1000 because it’s automatically managed by the system once you define the discovery-interface under the vlt-domain. That port-channel is reserved specifically for VLTi, and its membership gets auto-populated based on the interfaces listed in the discovery-interface command.

If the new interfaces aren’t showing up, make sure:

• They’re physically up and have matching settings (speed, duplex, MTU, etc.) on both switches.
• There are no config conflicts, like if they’re still part of another port-channel or have leftover config that might interfere.

@DELL-Erman O​ 

I verified everything, and the configurations match, also there is no leftover at its new setup.

When using SFS, you need to delete the SmartFabric cluster to change ports. I wanted to confirm that this is not required in full switch mode.

The only other potential issue I see is that the new ports are 100 Gb, while the current ports are 25 Gb. Could that be causing the problem?

The reference manual is vague about the requirements.

Je1000,

No, Full Switch Mode is not strictly required to configure VLT in OS10. However, whether you're operating in SFS mode or Full Switch Mode, the configuration behavior and flexibility differ significantly.

The key differences would be

Full Switch Mode

Recommended for manual VLT configuration.
Offers complete CLI control over VLT domain setup, port-channel assignments, VLANs, and spanning tree.
No restrictions from SmartFabric automation.
Ideal for custom topologies, mixed port speeds, and advanced routing.

SmartFabric Services (SFS) Mode

VLT is automatically configured as part of the SmartFabric cluster.
Port roles (e.g., server, uplink, VLTi) are assigned by the cluster.
Changing port roles often requires deleting and recreating the cluster.
Not suitable for manual VLT configuration or mixed-speed VLTi links.

The speed mismatch is a valid concern, as OS10 VLT requires that VLTi ports be identical in speed and configuration, so If one peer uses 100 Gb ports and the other uses 25 Gb, the VLTi may fail to establish or behave unpredictably.

Let me know if this helps.

@DELL-Chris H ​ 

Can you please confirm that in Full Switch Mode, changing the VLTi ports is supported?

As for the port mismatch, it’s not between switches. I only have two switches, but the working ports are 25 Gb, and I’ve now connected the 100 Gb ports. However, they’re not being discovered or automatically added to port-channel 1000

Yes changing VLTi ports is supported in Full Switch mode., to include using 100 Gb interfaces, provided the following conditions are met:
Manual configuration is required

VLTi ports are not auto-discovered.

You must configure the new 100 Gb ports as discovery interfaces in the VLT domain.

So to use 100 Gb ports (e.g., ethernet 1/1/33 and 1/1/34) as VLTi, you would need:

OS10(config)# interface range ethernet 1/1/33-1/1/34
OS10(conf-range)# no switchport
OS10(conf-range)# exit

(Leaving switchport mode enabled on VLTi ports will prevent them from being used)

OS10(config)# vlt-domain 1
OS10(conf-vlt-1)# discovery-interface ethernet 1/1/33
OS10(conf-vlt-1)# discovery-interface ethernet 1/1/34

This should cause port-channel 1000 to be automatically created and mapped to the specified interfaces.

@DELL-Chris H ​ 

this is what its set and its not working 

I am having the same issue on Dell S4148F-ON switches, except no discovery ports are showing on POs for either switch. Have defaulted both switches and only built VLT domain, POs, MGMT interfaces, and set discovery interfaces to no switchport, but still same issue. Although switches can ping each other via MGMT interface, VLT election role fails to start, both switches think they are in the primary role, and new VLANS (include default VLAN 1) will not "import" into PO1000. 

I have two S4148T-ONs with running/working VLTs, and two S5232Fs also running VLTs with no issues, so I am at a loss on this. Basic config is below, any help is appreciated. 

hostname SW1
!
vlt-domain 1
 backup destination 10.100.100.41 interval 20
 delay-restore 100
 discovery-interface ethernet1/1/29-1/1/30
 peer-routing
 primary-priority 150
 vlt-mac e2:1a:2b:3c:4d:5e
!
interface port-channel1
 description "100 GB VLT PEER LINK"
 no shutdown
 switchport mode trunk
 switchport access vlan 1
 vlt-port-channel 1
 !
 interface ethernet1/1/29
 no shutdown
 no switchport
 no flowcontrol receive 
 no flowcontrol transmit
 !
 interface ethernet1/1/30
 no shutdown
 no switchport
 no flowcontrol receive 
 no flowcontrol transmit
 !
 interface mgmt1/1/1
 no shutdown
 no ip address dhcp
 ip address 10.100.100.42/24
 no ipv6 enable 

hostname SW2
!
vlt-domain 1
 backup destination 10.100.100.42 interval 20
 delay-restore 100
 discovery-interface ethernet1/1/29-1/1/30
 peer-routing
 primary-priority 250
 vlt-mac e2:1a:2b:3c:4d:5e
!
interface port-channel1
 description "100 GB VLT PEER LINK"
 no shutdown
 switchport mode trunk
 switchport access vlan 1
 vlt-port-channel 1
 !
 interface ethernet1/1/29
 no shutdown
 no switchport
 no flowcontrol receive 
 no flowcontrol transmit
 !
 interface ethernet1/1/30
 no shutdown
 no switchport
 no flowcontrol receive 
 no flowcontrol transmit
 !
 interface mgmt1/1/1
 no shutdown
 no ip address dhcp
 ip address 10.100.100.41/24
 no ipv6 enable

SW1# show vlt 1
Domain ID                  : 1
Unit ID                    : 2
Role                       : primary
Version                    : 2.3
Local System MAC address   : f0:d4:e2:29:e9:d6
Role priority              : 150
VLT MAC address            : e2:1a:2b:3c:4d:5e
IP address                 : fda5:74c8:b79e:1::2
Delay-Restore timer        : 100 seconds
Peer-Routing               : Enabled
Peer-Routing-Timeout timer : 0 seconds
VLTi Link Status
    port-channel1000       : up

VLT Peer Unit ID    System MAC Address    Status    IP Address             Version
----------------------------------------------------------------------------------
  1                 f0:d4:e2:2a:33:d6      up       fda5:74c8:b79e:1::1   

SW1#show vlan
Codes: * - Default VLAN, M - Management VLAN, R - Remote Port Mirroring VLANs,
       @ – Attached to Virtual Network, P - Primary, C - Community, I - Isolated
Q: A - Access (Untagged), T - Tagged
    NUM    Status    Description                     Q Ports
*   1      Active                                    A Eth1/1/1-1/1/26,1/1/31-1/1/54 
                                                     A Po1 
    4094   Active                                    T Po1000 

SW2# show vlt 1
Domain ID                  : 1
Unit ID                    : 1
Role                       : primary
Version                    : 2.3
Local System MAC address   : f0:d4:e2:2a:33:d6
Role priority              : 250
VLT MAC address            : e2:1a:2b:3c:4d:5e
IP address                 : fda5:74c8:b79e:1::1
Delay-Restore timer        : 100 seconds
Peer-Routing               : Enabled
Peer-Routing-Timeout timer : 0 seconds
VLTi Link Status
    port-channel1000       : up

VLT Peer Unit ID    System MAC Address    Status    IP Address             Version
----------------------------------------------------------------------------------
  2                 f0:d4:e2:29:e9:d6      up       fda5:74c8:b79e:1::2 

SW2# show vlan
Codes: * - Default VLAN, M - Management VLAN, R - Remote Port Mirroring VLANs,
       @ – Attached to Virtual Network, P - Primary, C - Community, I - Isolated
Q: A - Access (Untagged), T - Tagged
    NUM    Status    Description                     Q Ports
*   1      Active                                    A Eth1/1/1-1/1/26,1/1/31-1/1/54 
                                                     A Po1 
    4094   Active                                    T Po1000 

Hello,

Core Configuration Steps (on both peers)

1. Enter Configuration Mode:
2. Create the VLT Domain: Use the same ID (e.g., 1) on both switches.
3. Configure VLT Interconnect (VLTi) Ports: Assign dedicated ports (e.g., ethernet 1/1/29, ethernet 1/1/30) for the VLTi, ensuring they are not in a standard switchport mode.
4. Set VLT Priority (Optional but Recommended): Assign different priorities (e.g., 10 for primary, 20 for secondary) to designate the primary peer.
5. Configure VLT Backup Link (Heartbeat): Set the management IP of the peer switch to monitor its status.
6. Configure VLT MAC (Optional but Recommended): Ensures consistent MAC for faster convergence.
7. Create VLT Port-Channel (for End Devices): Create a Port-Channel (LAG) and associate it with the VLT domain.
8. Assign Member Ports: Add physical ports to the Port-Channel (e.g., ethernet 1/1/3 and ethernet 1/1/4).
9. Configure VLANs & Spanning Tree: Ensure VLANs are created and Spanning Tree (RPVST+ is default) is handled correctly for loop prevention, often by blocking one side of the VLT Port-Channel on the end device for redundancy. 

OS10(config)# interface range ethernet 1/1/3-1/1/4
OS10(config-if-range)# no switchport # For server-facing ports if needed
OS10(config-if-range)# channel-group 100 mode active # Or 'lacp'

OS10(config)# interface port-channel 1 # Or any unused Po number
OS10(config-if-Po100)# vlt-port-channel 1

OS10(conf-vlt-domain)# vlt-mac e2:1a:2b:3c:4d:5e

OS10(conf-vlt-domain)# back-up destination 10.100.100.41

OS10(conf-vlt-domain)# primary-priority 150 # On Primary Peer
OS10(conf-vlt-domain)# primary-priority 250 # On Secondary Peer

OS10(conf-vlt-1)# discovery-interface ethernet 1/1/29
OS10(conf-vlt-1)# discovery-interface ethernet 1/1/30
OS10(conf-vlt-1)# peer-routing
OS10(conf-vlt-1)# delay-restore 100

OS10(config)# vlt domain 1

OS10# configure terminal

by default STP , Rapid-pvst enabled dell switches.

We ask that you power off both switches first then power on the primary and login to switch and check their role, then power on the secondary switch and login into switch then check their role as well.

The issues will be fixed by rebooting both switches one by one.