STP Cheat Sheet Flashcards
Legacy Spanning Tree port states
Disabled, Blocking, Listening, Learning, Forwarding
Rapid Spanning Tree port states
Discarding, Learning, Forwarding
Default timers for STP
Hello:
Forward Delay:
Max Age:
Hello: 2s
Forward Delay: 15s
Max Age: 20s
Bridge ID format for STP
Priority…4-bit bridge priority (configurable from 0 to 61440 in increments of 4096)
System ID Extension…12-bit value taken from VLAN number
MAC Address…48-bit unique identifier
Path selection for STP
- )
- )
- )
- )
- ) Bridge with lowest root ID becomes root
- ) Prefer the neighbor with the lowest cost to root
- ) Prefer the neighbor with the lowest bridge ID
- ) Prefer the lowest sender port ID
What does PortFast do
Enables immediate transition into the forwarding state
What does UplinkFast do
Enables switches to maintain backup paths to root.
This is to enable the blocked port when the root port link is failed
What does BackboneFast do
Enables immediate expiration of the Max Age timer in the . event of an indirect link failure
What is Error-disable?
Err-disable is a feature that automatically disables a port on a Cisco Catalyst switch. When a port is error disabled, it is effectively shut down and no traffic is sent or received on that port
What is Root Guard?
Prevents a port from becoming the root port
What is BPDU Guard?
Error-disables a port if a BPDU is received
What is Loop Guard?
Prevents a blocked port from transitioning to listening after the Max Age timer has expired
What is BPDU Filter
Blocks BPDUs on an interface (disables STP)
RSTP Link Type:
Point-to-Point
Connects to exactly one other bridge (full duplex)
RSTP Link Type:
Shared
Potentially connects to multiple bridges (half duplex)
