Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Attention: The Community will be in read-only mode on 12/14/2017 from 12:00 am pacific to 11:30 am.

During this time you will only be able to see content. Other interactions such as posting, replying to questions, or marking content as helpful will be disabled for few hours.

We apologize for the inconvenience while we perform important updates to the Community.

MSTP L2 VLAN Databse Query !

Dear All

Regarding the MSTP configuration is it mandatory to create all the L2 VLANs in the VLAN Database for which we creating instance-to-vlan mapping.


In a bigger network with lots of switches why do we need to create
those L2 VLANS on a Switch for which its not catering any traffic.

Please help to confirm the same.

Regards

Varma

Everyone's tags (1)
1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

MSTP L2 VLAN Databse Query !

Hello Varma,

Regarding the MSTP configuration is it mandatory to create all the L2  VLANs in the VLAN Database for which we creating instance-to-vlan  mapping.

No, creating the VLANs is not required at all. What is required is to have the VLANs mapped into individual instances, and have the mapping (along with the MST region name and revision number) identical throughout the MST region.

Mapping an VLAN into an MST instance and creating that VLAN are two independent things. You can map non-existent VLANs into MST instances beforehand, and create them later (or never create them, according to your needs).

There is a different issue not related to MSTP at all - if a switch is a transit switch for a VLAN, then this VLAN must be created on this switch if even if there are no access ports configured for that VLAN. A switch will not accept frames in VLANs (on trunks) that are not created on the switch itself.

Best regards,

Peter

4 REPLIES
Cisco Employee

MSTP L2 VLAN Databse Query !

Hello Varma,

Regarding the MSTP configuration is it mandatory to create all the L2  VLANs in the VLAN Database for which we creating instance-to-vlan  mapping.

No, creating the VLANs is not required at all. What is required is to have the VLANs mapped into individual instances, and have the mapping (along with the MST region name and revision number) identical throughout the MST region.

Mapping an VLAN into an MST instance and creating that VLAN are two independent things. You can map non-existent VLANs into MST instances beforehand, and create them later (or never create them, according to your needs).

There is a different issue not related to MSTP at all - if a switch is a transit switch for a VLAN, then this VLAN must be created on this switch if even if there are no access ports configured for that VLAN. A switch will not accept frames in VLANs (on trunks) that are not created on the switch itself.

Best regards,

Peter

MSTP L2 VLAN Databse Query !

Hi Peter

Thanks a lot for the quick response and clarifications. Thus helps in my current network scenario.

Regards

Varma

Cisco Employee

MSTP L2 VLAN Databse Query !

Varma,

You're very much welcome.

Best regards,

Peter

MSTP L2 VLAN Databse Query !

Hi Varma,

just to add to my Master(Peter)'s comments. the default MST instance 0 has all the vlans mapped to it. Does it mean that we create all the vlans in the database and on every transit switch? NO. We only create the ones we using and we create them on the switches transiting those vlans. see below what i mean.

S1(config)# spanning-tree mst configuration
S1(config-mst)# show current
Current MST configuration
Name      []
Revision  0     Instances configured 1

Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-4094
-------------------------------------------------------------------------------
S1(config-mst)# instance 1 vlan 20,40
S1(config-mst)# show pending
Pending MST configuration
Name      []
Revision  0     Instances configured 2

Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-19,21-39,41-4094
1         20,40

HTH

Kishore

436
Views
0
Helpful
4
Replies
CreatePlease to create content