Spanning Tree Protocol

2023-10-1

STP alone is an L2 protocol. Per VLAN spanning tree PVST and Rapid STP, RSTP improve original standard.

STP prevents:

• broadcast storms
• multiple frame transmission
• MAC database instantiating

STP puts some parts in blocking state to prevent loops.

Interfaces/ports are either in blocking/forwarding state.

STP config is exchanged by interfaces every 2 seconds, using a multicast frame (BPDU), bridge protocol dataunit.

Bridge ID

Rapid PVST+

RSTP runs for each VLAN. High demand for resources.

RSTP calls blocking the discarding state. It also removes listening state and just calls it discarding.

Adds more port rules:

• Alternate, Backup, Disabled
• Alternate: suboptimal BPDU

commands:

spanning-tree vlan 1 root primary
spanning-tree vlan 1 root secondary

primary # set in 4096 increments.

commands:

show spanning-tree

Cisco Portfast

commands:

conf t
    # switchport mode access
    # spanning-tree portfast
    # spanning-tree bpduguard enable