Rapid Spanning Tree Protocol (RSTP/802.1w) is an evolution of classic STP that significantly reduces network convergence time from up to 50 seconds down to just a few seconds by replacing timer-based transitions with an active negotiation mechanism between switches.
Rapid PVST+ is Cisco's proprietary enhancement to the 802.1w standard that runs a separate RSTP instance for each VLAN, enabling load balancing across different VLANs by blocking different ports per VLAN.
RSTP uses a bridge-to-bridge handshake mechanism that allows ports to move directly to the forwarding state without waiting through transitional states, which is fundamentally different from classic STP's timer-based approach.
RSTP incorporates several optional classic STP features by default, including UplinkFast, BackboneFast, and PortFast functionality, eliminating the need to manually configure these features.
Standard
IEEE Number
Cisco Version
Instances
Load Balancing
Classic STP
802.1D
PVST+
1 (IEEE) / Per-VLAN (Cisco)
No (IEEE) / Yes (Cisco)
Rapid STP
802.1w
Rapid PVST+
Multiple STP
802.1s
Same (no Cisco version)
Groups of VLANs
Yes
RSTP State
Classic STP Equivalent
Sends/Receives BPDUs
Learns MACs
Forwards Data
Discarding
Disabled, Blocking, Listening
Receives only
No
Learning
Forwarding
Role
Description
Root Port
Port closest to root bridge (lowest root cost) - unchanged from STP
Designated Port
Port sending best BPDU on a segment - unchanged from STP
Alternate Port
Discarding port receiving superior BPDU from another switch (backup to root port)
Backup Port
Discarding port receiving superior BPDU from same switch (only with hubs)
Link Type
Connection
Duplex Mode
Configuration
Edge
End host
Full
spanning-tree portfast
Point-to-Point
Direct switch-to-switch
spanning-tree link-type point-to-point
Shared
Hub connection
Half
spanning-tree link-type shared
Speed
RSTP Cost
Classic STP Cost
10 Mbps
2,000,000
100
100 Mbps
200,000
19
1 Gbps
20,000
4
10 Gbps
2,000
2
100 Gbps
200
N/A
1 Tbps
20
Classic STP (802.1D): Protocol Version 0
Rapid STP (802.1w): Protocol Version 2
Neighbor loss detection: 3 missed BPDUs = 6 seconds (vs. 20 seconds in classic STP)
Hello timer: 2 seconds (same as classic STP)
Feature
RSTP
Convergence Time
30-50 seconds
Few seconds
Port States
5
3
Port Roles
BPDU Origin
Root bridge only
All switches
BPDU Flags Used
2 bits
8 bits
Neighbor Timeout
20 seconds (10 hellos)
6 seconds (3 hellos)
Protocol Version
0
Purpose
Configuration in RSTP
PortFast
Edge ports move directly to forwarding
Configure as edge port
UplinkFast
Alternate port immediately becomes root port if root port fails
Automatic
BackboneFast
Rapid response to indirect link failures
Don't confuse link types with port roles or port states - They are separate concepts
Link types: Edge, Point-to-Point, Shared
Port roles: Root, Designated, Alternate, Backup
Port states: Discarding, Learning, Forwarding
Alternate vs Backup ports - Both are discarding, but:
Alternate = superior BPDU from different switch
Backup = superior BPDU from same switch (hub scenario only)
CLI shows "BLK" even in RSTP - The state is actually called "Discarding" in RSTP terminology
RSTP compatibility - RSTP is backward compatible with classic STP; interfaces connected to classic STP switches will operate in classic STP mode
Edge port configuration - Use spanning-tree portfast, NOT spanning-tree link-type edge
spanning-tree link-type edge
Protocol versions - Classic STP = 0, RSTP = 2 (not 1!)
RSTP Port Costs Pattern: Start with 2,000,000 for 10 Mbps, divide by 10 for each speed increase
10 Mbps = 2,000,000
100 Mbps = 200,000
1 Gbps = 20,000
Pattern: 2-2-2-2-2-2 (just move decimal)
"A-B" for Non-Designated Roles:
Alternate = Another switch
Backup = Same Box (same switch)
RSTP States = "DLF": Discarding → Learning → Forwarding
3-3-3 Rule for RSTP:
3 port states
3 missed BPDUs = neighbor lost
3 link types
"Evolution, not Revolution": RSTP keeps same root bridge, root port, and designated port election rules
If SW3 receives a superior BPDU on G0/1 from SW2 → Alternate port (different switch)
If SW2 receives its own BPDU back through a hub on G0/2 → Backup port (same switch)
Hub doesn't participate in STP (no cost added)
If costs are equal through hub, use neighbor bridge ID as tiebreaker
Then use neighbor port ID if still tied
Command
spanning-tree mode rapid-pvst
Enable Rapid PVST+
Configure edge port
Manually set point-to-point
Manually set shared link
show spanning-tree
Verify STP status (shows "rstp" for protocol)
What is the main difference between RSTP and classic STP convergence mechanisms?
Classic STP uses timer-based transitions (30-50 seconds), while RSTP uses a bridge-to-bridge handshake/negotiation mechanism allowing ports to move directly to forwarding (few seconds).
What are the three RSTP port states?
Discarding (combines Disabled, Blocking, Listening)
What are the four RSTP port roles?
What is an RSTP Alternate Port?
A discarding port that receives a superior BPDU from another switch. It functions as a backup to the root port and can immediately become the root port if the current root port fails.
What is an RSTP Backup Port?
A discarding port that receives a superior BPDU from another interface on the same switch. This only occurs when connected to a hub. It serves as a backup for a designated port.
What are the RSTP port costs for 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps?
10 Gbps = 2,000
What protocol version number is in a classic STP BPDU vs RSTP BPDU?
Classic STP: Version 0
RSTP: Version 2
How long does RSTP wait before considering a neighbor lost?
3 missed BPDUs = 6 seconds (compared to 20 seconds/10 hello intervals in classic STP)
What three classic STP optional features are built into RSTP?
PortFast (edge ports)
UplinkFast (alternate port becomes root port immediately)
BackboneFast (rapid response to indirect failures)
What are the three RSTP link types?
Edge - connected to end hosts (full duplex)
Point-to-Point - direct switch-to-switch (full duplex)
Shared - connected to hub (half duplex)
How do you configure an RSTP edge port?
Use the command spanning-tree portfast on the interface (same as classic STP PortFast)
What is IEEE 802.1D?
Classic Spanning Tree Protocol - original STP with one instance for all VLANs, cannot load balance
What is IEEE 802.1w?
Rapid Spanning Tree Protocol - faster convergence than 802.1D, but still only one instance for all VLANs
What is IEEE 802.1s?
Multiple Spanning Tree Protocol (MSTP) - groups multiple VLANs into instances for load balancing
What is Cisco's Rapid PVST+?
Cisco's upgrade to 802.1w that runs a separate RSTP instance per VLAN, allowing load balancing by blocking different ports in each VLAN
What happens when an RSTP switch connects to a classic STP switch?
The RSTP switch interfaces connected to the classic STP switch will operate in classic STP mode (backward compatible), while other interfaces remain in RSTP mode.
In RSTP, which switches originate BPDUs?
ALL switches originate and send their own BPDUs from designated ports (unlike classic STP where only root bridge originates BPDUs)
How many bits of the BPDU flags field does RSTP use vs classic STP?
Classic STP: 2 bits (1st and 8th)
RSTP: All 8 bits (used for negotiation process)
What action does an RSTP switch take when it loses a neighbor?
It flushes (deletes) all MAC addresses learned on that interface since it can no longer reach destinations through that interface.
What is the default STP mode on modern Cisco switches?
Rapid PVST+ (rapid-pvst)
Which command enables Rapid PVST+ mode?
What does show spanning-tree display for the protocol when running Rapid PVST+?
It shows "rstp" as the protocol
Why is MSTP (802.1s) better than Rapid PVST+ for large networks?
MSTP can group multiple VLANs into instances (e.g., VLANs 1-100 in instance 1), making it easier to manage than configuring separate root bridges for each VLAN in Rapid PVST+.
What determines which port becomes the designated port vs backup port when two ports on the same switch connect to a hub?
The interface with the lowest port ID becomes the designated port; the other becomes the backup port.
Does Cisco have its own version of MSTP?
No, Cisco devices run the industry standard 802.1s MSTP.
Why was the Listening state removed in RSTP?
RSTP's negotiation mechanism and built-in features (UplinkFast, BackboneFast) make the listening state unnecessary - ports can move directly to Learning or Forwarding when appropriate.
What determines if a connection is point-to-point or shared in RSTP?
Duplex mode - full duplex = point-to-point, half duplex = shared. The switch auto-detects this.
Command to manually configure point-to-point link type?
Command to manually configure shared link type?
Which STP version is specifically mentioned in the CCNA exam topics?
Rapid Spanning Tree (RSTP/Rapid PVST+)
Last changed15 days ago