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Webcast-Catalyst9k
New Member

Spanning-tree

Can somebody please explain what the difference is between the Root ID and the Bridge ID in spanning-tree

2 REPLIES
Gold

Re: Spanning-tree

STP Bridge ID is 8 bytes in length. First two bytes are the STP Bridge Priority of the local bridge/switch you're looking at, which ranges from 0 to 65535 (default is 32768). The remaining 6 bytes are a MAC address assigned to that bridge/switch.

When STP Root Bridge election takes place, bridges/switches exchange Bridge IDs with each other. The one advertising the lowest value (highest priority) Bridge Priority wins the election. In the case of a tie on Bridge Priority, the MAC address is used to break the tie; again, the one with the lowest value wins.

STP Root ID is the Bridge ID of the current bridge/switch that is acting as the Root Bridge for a particular Spanning Tree.

When Root ID and Bridge ID are the same on a local bridge/switch, you're looking at the Root Bridge itself.

Hope this helps.

New Member

Re: Spanning-tree

Thanks for that, I had a look at the Cisco Press book on LAN Switching and found exactly what I was looking for in the sample chapter.

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