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gwhuang5398
Explorer

Is "spanning-tree vlan priority 0" valid?

3560 command reference says valid priority values are 4096, 8192, ... however I tried "spanning-tree vlan priority 0" and the command was accepted. When I "show spanning-tree brief", the vlan I configured did show priority 0.

Did I read the command reference right? (I looked at 12.2(44) and 12.2(52)

Is "priority 0" a valid configuration even if IOS accepts it?

Thanks

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Accepted Solutions
jonatrod
Rising star

Good morning gwhuang5398

My name is Johnnatan and I am part of the Small business Support community.  This is a valid value for this command, actually has more priority than 4096. The priority order starts from 0 and then increases in 4096.

     0, 4096, 8192, 12288, …

If you configure two switches one of them with priority ¨0¨ and the other one with priority  ¨4096¨, the first one with priority ¨0¨ is going to be the root.

I hope you find this answer useful, if it was satisfactory  for you, please mark the question as Answered.

Thank you.

Johnnatan Rodriguez Miranda.

Cisco Network Support Engineer.

“Please rate useful posts so other users can benefit from it” Greetings, Johnnatan Rodriguez Miranda. Cisco Network Support Engineer.

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2 REPLIES 2
jonatrod
Rising star

Good morning gwhuang5398

My name is Johnnatan and I am part of the Small business Support community.  This is a valid value for this command, actually has more priority than 4096. The priority order starts from 0 and then increases in 4096.

     0, 4096, 8192, 12288, …

If you configure two switches one of them with priority ¨0¨ and the other one with priority  ¨4096¨, the first one with priority ¨0¨ is going to be the root.

I hope you find this answer useful, if it was satisfactory  for you, please mark the question as Answered.

Thank you.

Johnnatan Rodriguez Miranda.

Cisco Network Support Engineer.

“Please rate useful posts so other users can benefit from it” Greetings, Johnnatan Rodriguez Miranda. Cisco Network Support Engineer.

Hi Jonatrod,

when two switches are set with "priority 0" the first, and "root primary" the second,

which will become root-bridge? Some say the second, most say the first.

IMHO, if I'm not wrong, the second Switch generates a Syslog complaining it can't

grant to become root-bridge, because of the presence in the network of the

"priority 0" Switch (it cannot set himself 4096 below).

So I think the two switches will set both to "priority 0", and tie break on their MAC...

The lowest MAC generates a lowest BID, and this will decide the root-bridge. Isn't it?