@It seems that I have to delete this question. Before I do, I would appreciate it if tell me why it is off-topic.

The default gateway on PC1 is 10.10.0.3. but I got your point and it is consistent with what I found out.

@Zac67 Unfortunately, no answer could address my question in a fulfilling way. I hope somebody in the foreseeable future can answer the question persuasively.

I think I am missing something. but as I see it now. portfast with or without bpduguard allows forwarding until 1st bpdu received. then with or without bpdugard forwarding will be stopped. in bpduguard case by disabling the port. otherwise by entering LSN/LRN states. FWD then will be resumed after STP is stable again. So, I see they are different ways to handle it rather than bpduguard being more secure. So, is this correct, or I am missing something as I said. Please elaborate as I am a novice, and can miss what you understand intutively/

6- What does happen if the portfast port does not receive the 1st bpdu for a considerable amount of time for whatever reason? Should not be there a better way to guard the port that disables it immediately without having to wait for the 1st bpdu?

4- If No, then what does happen in this case, and if Yes, Then STP is going to be stable again even after a bit longer time. So, Is bpduguard really crucial or necessary in the modern fast networks, or just a recommendation? 5- If there is something I am not seeing or I am misunderstanding. what is it? and how does the process happen in both cases (bpduguard on/off) in this case? Thanks again

@RonTrunk Thanks, but I think my main inquiries have not been fully addressed. what I do want to know: 1- isn't there an equal chance in both cases for loop formation before 1st bpdu received? (Yes/No) 2-if Yes, then no difference at this stage, if No, what is the difference? 3- if all bpdu features are off including bpduguard and except portfast, does the port revert back to normal LSN/LRN/FWD. (Yes/No). (to be continued...)

I have been reading that bpduguard is a good safeguard for portfast ports. I understand they are separate, but they are strongly related. Even the command to enable bpduguard has the portfast keyword. However, I see that portfast is capable of handling the wrong connections. so what is the real use and benefit of bpduguard?

Thanks again. As I said in a previous comment, I think I am missing something. but as I see it now. portfast with or without bpduguard allows forwarding until 1st bpdu is received. then with or without bpduguard forwarding will be stopped. in bpduguard case by disabling the port, otherwise by entering LSN/LRN states. FWD then will be resumed after STP is stable again. So, I see they are different ways to handle it rather than bpduguard being more secure. So, is this correct, or I am missing something as I said? Please elaborate as I am a novice and can miss what you understand intuitively.

@RonMaupin, Please see the three comments above. I think I am missing something. but as I see it now. portfast with or without bpduguard allows forwarding until 1st bpdu received. then with or without bpdugard forwarding will be stopped. in bpduguard case by disabling the port. otherwise by entering LSN/LRN states. FWD then will be resumed after STP is stable again. So, I see they are different ways to handle it rather than bpduguard being more secure. So, is this correct, or I am missing something as I said. Please elaborate as I am a novice, and can miss what you understand intutively.

@Marc'netztier'Luethi 7- What does happen if the portfast port does not receive the 1st bpdu for a considerable amount of time for whatever reason? Should not be there a better way to guard the port that disables it immediately without having to wait for the 1st bpdu?

@Marc'netztier'Luethi 4- If No, then what does happen in this case, and if Yes, Then STP is going to be stable again even after a bit longer time. So, Is bpduguard really crucial or necessary in the modern fast networks, or just a recommendation? 5- If there is something I am not seeing or I am misunderstanding. what is it? and how does the process happen in both cases (bpduguard on/off) in this case? Thanks again

@Marc'netztier'Luethi Thanks, but I think my main inquiries have not been fully addressed. what I do want to know: 1- isn't there an equal chance in both cases for loop formation before 1st bpdu received? (Yes/No) 2-if Yes, then no difference at this stage, if No, what is the difference? 3- if all bpdu features are off including bpduguard and except portfast, does the port revert back to normal LSN/LRN/FWD. (Yes/No). (to be continued...)