Root Switch Election Procedure - Supermicro SSE-F3548S User Manual

•Receives BPDUS
Blocking •Discards packets
•Does not learn MAC
Listening
Since spanning tree forms a logical loop-free topology, it helps to have physical loop connections on the
network for redundancy purposes. When an active connection fails, spanning tree automatically enables
the blocked redundant connection.
Rapid Spanning Tree Protocol (RSTP) provides faster topology convergence. Spanning tree (STP) takes
more than 30 seconds to move a port to a forwarding state, but RSTP can move a port to the forwarding
state within 3 times of the hello interval (default hello interval is 2 seconds). RSTP is compatible with STP.
Multiple Spanning Tree Protocol (MSTP) extends RSTP to provide separate spanning trees for different
VLANs or VLAN groups. This helps to use alternate paths efficiently by blocking the ports only for the
required VLANs. MSTP is compatible with RSTP.

6.1 Root Switch Election Procedure

Spanning tree protocol selects one switch as the root switch for every switched LAN. This root switch is
used as the reference point to decide the spanning tree topology. Based on the connections to this root
switch, the redundant links on the LAN are identified and blocked. Spanning tree runs an election process
to elect one switch as the root switch.
Spanning tree selects the switch with the lowest bridge ID as the root switch. Every switch on the LAN has
a bridge ID.The bridge ID has two components: the priority and the MAC address of the switch. The
spanning tree priority occupies the most significant two bytes of the bridge ID. The default spanning tree
priority is 32768.
STP Priority - 2 bytes
(Default 32768)
•Receives BPDUs
•Discards packets
•Does not learn MAC
•Receives BPDUs
•Discards packets
Learning
•Learns MAC addresses
Forwarding
Switch MAC – 6 bytes
Bridge ID
Supermicro SSE-F3548S/SSE-F3548SR Configuration User's Guide
Disabled
•Does not receive BPDUs
•Discards packets
•Does not learn MAC
•Receives BPDUs
•Forwards packets
•Learns MAC addresses
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