No link (flapping) between 2 SG250 switches with 100m CAT6

[swbsf]

Hello there,

I'm not quite sure what conclusion I should jump to, any help is greatly appreciated. Here is our setup : We got 2 brand new SG250-26 connected over a 100meter long CAT6 RJ45, and connection is not coming up. It is actually flapping, as in this log :

2147474608 	2018-Oct-16 06:10:26	Warning 	%LINK-W-Down:  gi3   
2147474609 	2018-Oct-16 06:10:26	Informational 	%LINK-I-Up:  gi3   
2147474610 	2018-Oct-16 06:10:04	Warning 	%LINK-W-Down:  gi3   
2147474611 	2018-Oct-16 06:10:03	Informational 	%LINK-I-Up:  gi3   
2147474612 	2018-Oct-16 06:09:52	Warning 	%LINK-W-Down:  gi3   
2147474613 	2018-Oct-16 06:09:52	Informational 	%LINK-I-Up:  gi3   

My best bet would be a damaged cable of course, but what I don't undertand is whether I connect a laptop or another NoName switch, connection comes up right away, so the cable explanation is not enough. I obviously tested on different ports and even upgraded to latest firmware. Reset to factory default didn't help either.

This makes just no sense to me.

Thanks for your time! (Attached a full conf dump)

[Leo Laohoo · Accepted solution]

100 metres. Hmmmm ...
What happens if you change the port speed to 100 Mbps?

[swbsf]

2147474060 	2018-Oct-16 07:06:05	Informational 	%LINK-I-Up:  gi3   

You're the man, nice check. So I guess I can not force Gbit on this cable?

[Leo Laohoo]

For GigabitEthernet, the standard is <100 metres ... that is if the cable is of good quality.
Chop 5 metres from the cable and see if it'll work.

[swbsf]

Ok I'll try this, thank you very much @Leo Laohoo

[Leo Laohoo]

Happy to be of assistance.