spanning-tree extend system-id

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Nov 17th, 2009
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I want to create new vlan id but i get message "% Failed to create VLANs xxxx

Spanning-tree extend system-id need to be enabled." If i enable that is there going to be any changes or break in spannintree topology.



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Giuseppe Larosa Tue, 11/17/2009 - 04:40
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Hello Juha,

the command

spanning-tree extend system-id

has an effect on the way the bridge-id for each vlan/instance is created.

old way:

a different mac address for each vlan taken from internal block

same priority value for all vlans

new way:= extend systemid

use only one MAC but priority is built as

base_value + vlan#

base_value is a multiple of 4096.

bridge-id = priority+ MAC address

it changes the bridge-id for each vlan this may change the root bridge in some vlan.

But the impact should be limited

the reason for this is to avoid to waste MAC addresses.

your switch has probably used all internal MAC addresses.

Hope to help



I have 3 distro switch have a priority value of 16384. The main distro switch connected to my router has a value of 8192.

I, too, received the same message when I attempted to create VLAN1725.  I have successfully created the SVI for the said VLAN.  Should I enable spanning-tree extend system-id during after-hours?  You mentioned that the impact is limited, what's the worst thing that could happen?

Thank you.


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