The Tech Blog of a Sysadmin.

Configuring VLT on a Dell S4148T-ON Switch

For those out there looking at replacing their ToR switches, the Dell S4148T-ON is a compelling choice. A quick look through the spec sheet reveals they are eminently capable, and available at a very competative rate when compared with equivalent switches available from Dells competitors.

One Quirk i discovered how ever after aquiring a pair of these switches with an OS10 license, was that stacking had been removed as a feature of the OS. VLT was available in OS9 alongside stacking, but in OS10 the OS requires the use of VLT if you would like to aggregate channel groups between switches in the same fashion as stacking.

There are a few important things to remember when configuring VLT in OS10, and there is plenty of literature and guides out there designed for OS9 that will lead you astray;

- OS10 chooses which VLANs traverse the VLT link between the switches via VLTi, do not add any VLANs to this link

- Ensure the spanning tree protocol used between switches and neighboring switches is identical

- Ensure VLT peers are running identical firmware revisions

- don't attempt to manually configure channel groups then add those to the VLTi link, instead add the physical interfaces


The commands are fairly straight forward once you have your base config down;


-  conf#vlt domain #

(creates domain, must be the same on the matching peer)

-  conf-vlt-# discovery-interface

(where you enter an interface or range of interfaces to be used for VLT)

-  conf-vlt-# backup x.x.x.x

(configure the IP for the backup interface, this is used for heartbeat backup timers and little else so i'd recommend using the management interface)

Now you create the port channel on each switch, and from the port channel menu issue the command;

-  conf-if-po-# vlt-port-channel

(This also has to correspond to the port channel number on the other switch to be part of the correct aggregration group)


I hope this run down proves useful to anyone who is using OS10 on the S series Dell switches and wishes to use VLT over stacking.








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