Difference between Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP) 1. The main difference between Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) and Spanning Tree Protocol (STP IEEE 802.1D) is that Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) assumes the three Spanning Tree Protocol (STP) ports states Listening, Blocking, and Disabled are same (these states do not forward Ethernet frames and they do not learn MAC addresses). Hence Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) places them all into a new called Discarding state. Learning and forwarding ports remain more or less the same.

1. Difference b/w STP, RSTP, PVST & MSTP
Difference between Spanning Tree Protocol (STP) and Rapid Spanning Tree
Protocol (RSTP)
1. The main difference between Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) and Spanning
Tree Protocol (STP IEEE 802.1D) is that Rapid Spanning Tree Protocol (RSTP IEEE 802.1W)
assumes the three Spanning Tree Protocol (STP) ports states Listening, Blocking, and Disabled are
same (these states do not forward Ethernet frames and they do not learn MAC addresses).
Hence Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) places them all into a new called
Discarding state. Learning and forwarding ports remain more or less the same.
2. In Spanning Tree Protocol (STP IEEE 802.1D), bridges would only send out a BPDU when they
received one on their Root Port. They only forward BPDUs that are generated by the Root Switch
(Root Bridge). Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) enabled switches send out
BPDUs every hello time, containing current information.
3. Spanning Tree Protocol (STP IEEE 802.1D) includes two port types; STP Root Port and Designated
Port. Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) includes two additional port types called
as alternate ports and backup ports.
An alternate port is a port that has an alternative path or paths to the Root Switch (Root Bridge) but is
currently in a discarding state (can be considered as an additional unused Root Port). A backup port is a
port on a network segment that could be used to reach the root switch, but there is already an active
STP Designated Port for the segment (can be considered as an additional unused designated port).
Table View
STP (802.1d) Rapid STP (802.1w)
In stable topology only the
root sends BPDU and relayed by
others.
In stable topology all bridges generate BPDU every Hello (2 sec) : used
as“keepalives” mechanism.
Port states
Disabled
Blocking
Listening
Learning
Forwarding
Discarding (replaces disabled, blocking and listening)
Learning
Forwarding

2. Difference b/w STP, RSTP, PVST & MSTP
To avoid flapping, it takes 3 seconds for a port to migrate from one protocol to another (STP / RSTP) in a
mixed segment.
Port roles
Root (Forwarding)
Designated (Forwarding)
Non-Designated (Blocking)
Root (Forwarding)
Designated (Forwarding)
Alternate(Discarding)Backup (Discarding)
Additional configuration to make
an end node port aport fast (in
case a BPDU is received).
- An edge port (end node port) is an integrated Link type which
depends on the duplex : Point-to-point for full duplex & shared for
half duplex).
Topology changes and convergence
Use timers for convergence
(advertised by the root):
Hello(2 sec)
Max Age(20 sec = 10 missed
hellos)
Forward delay timer (15 sec)
- Introduce proposal and agreement process for synchronization (< 1
sec).- Hello, Max Age and Forward delay timer used only for backward
compatibility with standard STP
Only RSTP port receiving STP (802.1d) messages will behaves as
standard STP.
Slow transition (50sec): Blocking
(20s) =>Listening (15s) =>Learning
(15s) =>Forwarding
Faster transition on point-to-point and edge ports only:Less states –
No learning state, doesn’t wait to be informed by others,
instead, actively looks for possible failure by RLQ (Request Link Query)
a feedback mechanism.
Use only 2 bits from the flag
octet:Bit 7 : Topology Change
Acknowledgment.Bit 0 : Topology
Change
Use other 6 bits of the flag octet (BPDU type 2/version 2):
Bit 1 : ProposalBit 2, 3 : Port roleBit 4 : LearningBit 5 : ForwardingBit 6
: AgreementBit 0, 7 : TCA & TCN for backward compatibility
The bridge that discover a change
in the network inform the root,
that in turns informs all others by
sending BPDU with TCA bit set and
instruct them to clear their DB
entries after “short timer”
(~Forward delay) expire.
TC is flooded through the network, every bridge generate TC
(Topology change) and inform its neighbors when it is aware of a
topology change andimmediately delete old DB entries.

3. Difference b/w STP, RSTP, PVST & MSTP
If a non-root bridge doesn’t receive
Hello for 10*Hello (advertised from
the root), start claiming the root
role by generating its own Hello.
Wait for 3*Hello on a root port (advertised from the root) before
deciding to act.
Wait until TC reach the root + short
timer (~Forward delay) expires,
then flash all root DB entries
Delete immediately local DB except MAC of the port receiving the
topology changes (proposal)
Difference between PVST+ (Per VLan Spanning Tree) & MST (Multiple
Spanning Tree)
1. PVST+ (Per VLan Spanning Tree)- It's difference from 802.1Q CST because instead of having
a single root switch for all VLAN, The PVST+ mean STP is run in each VLAN.
2. MST (Multiple Spanning Tree)- MST maps multiple VLANs into a spanning tree instance,
with each instance having a spanning tree topology independent of other spanning tree
instances.This architecture provides multiple forwarding paths for data traffic, enables load
balancing, and reduces the number of STP instances required to support a large number of
VLANs. MST improves the fault tolerance of the network because a failure in one instance
(forwarding path) does not affect other instances (forwarding paths).