RSTP forward delay

[Network Learner's]

Hello all,

Can anyone explain why RSTP does not have forward delay timers, and what are the port transitioning states.

[MHM Cisco World]

check also below

MHM

[Enes Simnica]

hello @Network Learner's. thats strange from the well knowsRSTP for sure lool. and usually rstp eliminates the forward delay timers used in traditional STP by introducing a more efficient handshake mechanism. Instead of waiting fixed intervals, RSTP ports actively negotiate transitions through proposal-agreement messages between switches, allowing faster convergence in just 1-2 seconds. RSTP simplifies port states to just three: Discarding (blocks traffic, similar to STP's disabled/blocking/listening), Learning (builds MAC tables but doesn't forward), and Forwarding. This streamlined approach removes STP's listening state and reduces delays by allowing stable ports to skip intermediate states when safe. The key improvement is replacing passive timers with active neighbor coordination for rapid failover. 

and G, if u have some labs that u dealing with, share it with me, lets dive deeper...

-Enes

[M02@rt37]

Hello @Network Learner's 

No forward delay timers because RSTP use rapid negotiation, link-type detection, and continuous BPDU exchange to converge quickly. Port roles and states are simplified as MHM show you, yet provide the same loop-protection, but with near-instant transitions...

[Network Learner's]

@MHM Cisco World As i understand port states of rstp and from some documents it is given yhat rstp does not have forward delays.

what are the forward delay timers as per your comment can you please explain.

i knew about proposal and agreement and rstp sends bpdu every 2 seconds as we do in a routing table and no TCN shared in this.

[MHM Cisco World]

https://youtu.be/i1CSbGeLBtE?si=l50yxwEtiqMYKLWF

[wajidhassan]

Hi @Network Learner's ,

RSTP (Rapid Spanning Tree Protocol) removes the traditional forward delay timer to speed up convergence. Instead of waiting for timers, RSTP uses proposal/agreement handshake to quickly transition ports.

The main port states in RSTP are:

• Discarding (combines blocking, listening, and disabled from STP)

• Learning

• Forwarding

This helps RSTP achieve faster topology changes compared to classic STP.

Hope this helps!

[Joseph W. Doherty]

Can anyone explain why RSTP does not have forward delay timers, and what are the port transitioning states.

I believe both questions were well answered in the other replies, but although rapid STP doesn't need forward delay timers, I believe it still supports them when working in conjunction with STP.

I also want to mention, rapid STP was enhanced/improved in many other ways too (including supporting some of Cisco's proprietary PVST enhancements).

[paul driver]

Hello
As stated by @Enes Simnica RSTP  (802.1w) doesn't rely on any timers it utilises an proposal/agreement
This proposal/agreement is embedded in a new BPDU format that is sent out as keepalives as you are aware every hello time (2 secs)  and if a port misses 3 x hellos then the switch will consider it a loss of connectivity and very quickly age out any information on that port.

This fast transition is subject to 2 things:
port is and edge port
       or
port link type is point-to-point (not shared/half duplex)

So now only non-edge ports can cause of a topology change, meaning any port transitioning into a blocking state doesn't initiate a TC in the stp domain as opposed to the older stp versions (802.1d)

Please note though any rstp and non rpvst integration the proposal/agreement is lost, and the older listening-learning sequence is used as a fall back.