Module 1 Lesson 3: STP

Used to prevent layer 2 bridging loops
PVST+ default
- One STP instance per VLAN
- Cisco proprietary

Phase I - Root Bridge Election
- "root" of the spanning-tree
- Election based on BID
- Bridge Priority
- MAC Address

Phase II - Root Port Election
- Upstream port closest to root bridge.


STP ROOT PORT ELECTION
- Upstream port closest to root bridge
- Root port election based on
- Lowest cumulative cost
- Inverse value based on interface bandwidth
- Lowest upstream BID
- Used to isolate multiple connections to upstream same bridge
- Lowest port ID
- Lowest port priority
- Lowest port number

Portfast
- Forward through listening and learning phases
BPDU Filter
- If BPDU is received revert out of portast state
BPDU Guard
- If BPDU is received shut port down
Root Guard
- If superior BPDU is received shut port down
Uplinkfast
- Immediately transition alternate ports to forwarding when root port is lost
BackboneFast
- Expire max age when inferior BPDU is received on root port
Loop Guard
- Prevent unidirectional links

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