Adding vlans to MSTP instances

[cmparish5]

We use an active/active configuration for our MSTP where instance 1 odd vlans is set with a lower priority on one core switch (making it the root bridge for odd vlans) and instance 2 for our even vlans is configured with a lower priority on the other core switch (making it the root bridge for even vlans).

Beneath the cores are a pair of Nexus 5k's with the hosts that will use a new even vlan.  On both 5k's I will add the new vlan into their instance 2.

We have other access switches as well beneath the cores, no hosts on these other switches will be using the new vlan.  But as they all use MST do I still need to update their instance 2 MST config?  

Because we have VTP working with the cores as our servers (note the 5k's do not use VTP so I'll manually add the new vlan to them) and the rest of the switches being clients, the new vlan will propogate down to them but their will be no hosts using them.  So if I do not update their MST instance 2, then that new vlan will be dumped into the default instance 0.  Will this cause issues?

[Andrew Khalil]

@cmparish5

Greetings,

Any created vlans that are not assigned to specific instance will be assigned automatically to the instance 0, and you will not need to create these vlans to the switches that will not use it! (of course if these switches are  VTP clients, so it will have these vlans automatically but anyway it will be useless because it's not used!).

But in case of updating any instance other than the default one in 1 switch, so you should update all switches as well, so if you added 1 more vlan to instance 2 in the core switch and the other switch that will use this new vlan, you have to update other switches even if they don't use this new created vlan!

Please don't forget to rate helpful responses and mark solutions!

It will be so nice from you!

Bst Rgds,

Andrew Khalil

[cmparish5]

So the other switches will get the new vlan anyway as they are VTP clients.  But I still need to update instance 2 in these switches with the new vlan, even if no hosts on those switches will use that vlan?

[Andrew Khalil · Accepted solution]

Again, if a vlan will be added to a specific instance (not the default one which is instance 0) like instance 2 for example, so you need to update the configuration of that instance in all switches even if they don't need to use it! 

but if you will add a new vlan without assigning it to a specific instance, it will be added automatically to instance 0 and in this case you don't need to add this vlan to any other switch (that is not VTP becasue VTP client will get it anyway) if it will not use it!

I hope my reply is helpful enough!

Please don't forget to rate any helpful responses and mark solutions!

Bst Rgds,

Andrew Khalil

[cmparish5]

Yup, I got ya now, thanks!

[Andrew Khalil]

Happy to help you! @cmparish5

Please don't hesitate to contact me if you need any further inquiry!

and don't forget to RATE any helpful response and MARK solutions!

It will be so nice from you!

Bst Rgds,

Andrew Khalil

[Andrew Khalil]

@cmparish5

Greetings,

Any created vlans that are not assigned to specific instance will be assigned automatically to the instance 0, and you will not need to create these vlans to the switches that will not use it! (of course if these switches are  VTP clients, so it will have these vlans automatically but anyway it will be useless because it's not used!).

But in case of updating any instance other than the default one in 1 switch, so you should update all switches as well, so if you added 1 more vlan to instance 2 in the core switch and the other switch that will use this new vlan, you have to update other switches even if they don't use this new created vlan!

Please don't forget to rate helpful responses and mark solutions!

It will be so nice from you!

Bst Rgds,

Andrew Khalil