What is the forward delay in STP?

Question

Little knowledge in this field any help would be appreciated. 

 

1.What are the port states in an STP implementation?
2.How does STP calculate its cost?
3.How long does it take to transition from blocking to forwarding?
4.What are the different types of STP available?

Answer 1

1. Port states in STP:

STP uses five port states. Disabled, Blocking, Listening, Learning, and Forwarding. Blocking is where the port is basically waiting and not passing traffic. Listening and Learning are the two stages it goes through before it can actually forward anything.

2. How STP calculates cost:

STP uses the bandwidth of the link to figure out the cost. Faster links have lower cost. For example, a 1‑gig port has a cost of 4, and a 100‑meg port has a cost of 19. If a gig port connects to a 100‑meg port, the whole link runs at 100 meg, so the cost is 19 on both sides.

3. How long it takes to go from blocking to forwarding:

Classic STP takes time because it goes through Listening and Learning. Each one is 15 seconds. So that’s 30 seconds total before it can forward traffic. If the switch has to wait out the Max Age timer first, that adds another 20 seconds, which is where the “50 seconds” number comes from.

4. Types of STP:

The main versions you’ll see are the original 802.1D STP, RSTP (802.1w), PVST+, Rapid‑PVST+, and MSTP. RSTP and Rapid‑PVST+ are the faster ones. MSTP lets you group VLANs together so you don’t have a separate STP instance for every single VLAN.

Answer 2

1- The five states of an STP port are:
-The disabled port state
-The blocking port state
-The listening port state
-The learning port state
-the forwarding port state.

 

2- The STP port cost basics are:
- for 1,000Mbs operating port the cost is 4 and for 100Mbps port the cost is 19.
- If a 1,000Mbps port is directly connected to a 100Mbps port between two switches, they will both be at the 100Mbps speed.

 

3- To transition from blocking to forwarding port takes 50 seconds delay

 

4- The known types of STP are:
- PVST+
- RSTP
- Rapid-PVST+
- MSTP