Speed and duplex strange issue

[ShoaibM]

Hi all,

I need to understand the speed and duplex settings of the port. I am trying to hard code the speed and duplex settings of the interface which apparently seems a simple procedure. So far what i have learned is you can hard code the interface speed and duplex settings. But in my lab i have the following situation.

                             Status "notconnect"
SW-3560 <-----------------------------> SW-2960
speed 100                                                         speed 100
duplex full                                                          duplex full

                             Status "notconnect"
SW-3560 <-----------------------------> SW-2960
speed 100                                                         speed 100
duplex auto                                                       duplex auto

                             Status "notconnect"
SW-3560 <-----------------------------> SW-2960
speed auto                                                        speed auto
duplex full                                                         duplex full

                             Status "connected"
SW-3560 <-----------------------------> SW-2960
speed 100                                                         speed auto
duplex full                                                          duplex auto

****** no "DUPLEX MISMATCH DISCOVERED" log messages ******

                             Status "connected"
SW-3560 <-----------------------------> SW-2960
speed auto                                                        speed 100
duplex auto                                                       duplex full

******* "DUPLEX MISMATCH DISCOVERED" log messages on both switches ******

**** if i run "sh controllers ethernet-controller fa 0/4" command on both switches. I can see collisions on 3560 interface in the "TRANSMIT" column and similarly on 2960 in the "RECIEVE" column.

Ports on both these switches are 10/100 capable.

I have tried to go through books, cisco online documents and previous community threads but so far i could not find anything which can explain this behaviour of the interface.

Any idea why is this?

Many thanks.

[Fotiosmark]

https://www.cisco.com/c/en/us/support/docs/lan-switching/ethernet/10561-3.html

[ShoaibM]

Thank you for your reply,
I have already gone through this document. Even if I set speed on both sides without making any change to other settings of the interface, even then the link goes down as I mentioned in my post. So something like below,

                                 Status "notconnect"
SW-3560 <-----------------------------> SW-2960
speed 100                                                         speed 100
duplex not set                                                    duplex not set

One thing more, that is
on 3560 i am using IOS Version 12.2(44)SE5
on 2960 i am using IOS Version 15.0(2)SE10a

Many thanks,

Kind Regards
Shoaib

[Georg Pauwen]

Hello,

are these 'real' switches, or are you using a simulator ?

[ShoaibM]

Thank for your response.
These are real hardware switches.
Kind regards

[Leo Laohoo]

If the gear are Cisco branded, it is no longer "best practice" to hard code speed and duplex on copper ports.  This is old, old, old school (mostly taught in Cisco courses and "old timers") & can make matters worst.

[ShoaibM]

Thank you Leo for your response.
I think you are right but why can't i hard code the interface. What is it that I am missing. The interface works fine if I connect the server but i can't hard code it if there is a switch on the other end.
Many thanks.

Kind Regards

[Leo Laohoo]

Do understand that when hard coding the speed & duplex it automatically disables MDI/MDI-X (much to the consternation of people). So my question is this: What kind of patch cable is used between the switch and the downstream machine?

[johnlloyd_13]

hi leo,

OP talks about old 3560 and 2960 switches which uses FE/100M ports. so it's still valid to hardcode and troubleshoot speed/duplex settings on these switches.

gigabitethernet technology fixed this issue and most of the time works when left in auto/auto.

[Leo Laohoo · Accepted solution]

---

@johnlloyd_13 wrote:

OP talks about old 3560 and 2960 switches which uses FE/100M ports.

---

Nope.  I disagree. 

Auto-negotiate feature was significantly improved since the introduction of the 3650/3750 and 2960 (compared to 2940/2950/2955 and 3550).  

My rule-of-thumb is simple:  If the switch supports MDI/MDI-X, then leave the ports to auto-negotiate unless otherwise.

[ShoaibM]

Thank you for your reply Leo.

I am using cat 6 straight cable. I will check with crossover cable and let you know.
Both switches support MDI-X feature. I think you are correct.

One more thing. Please see below,

                               Status "connected"
SW-3560 <-----------------------------> SW-2960
speed auto                                                         speed 100 <--- if manually set
duplex auto ("a-half")                                         duplex full <--- and set full
MDI-X on                                                           MDI-X off

                             Status "connected"
SW-3560 <-----------------------------> SW-2960
speed auto                                                         speed auto <--- if set auto
duplex auto ("a-full")                                          duplex full <--- and set full
MDI-X on                                                           MDI-X off

So 3560 is not picking up the correct duplex when i change speed on 2960 whereas 2960 does if i do the opposite. Is there any general explanation or this is just an isolated switch problem.

Many thanks.

[Leo Laohoo]

What are the exact IOS version both switches are running on?

[ShoaibM]

This is what I have.

2960

Switch       Ports      Model                         SW Version         SW Image
------      -----     -----                          ----------        ----------
* 1             50         WS-C2960-48TC-L    15.0(2)SE10a     C2960-LANBASEK9-M

3560

Switch       Ports     Model                       SW Version     SW Image
------      -----    -----                        ----------     ----------
* 1            52          WS-C3560-48PS    12.2(55)SE9    C3560-IPSERVICESK9-M

Many thanks.

[Leo Laohoo]

---

@ShoaibM wrote:

                               Status "connected"
SW-3560 <-----------------------------> SW-2960
speed auto                                                         speed 100 <--- if manually set
duplex auto ("a-half")                                         duplex full <--- and set full
MDI-X on                                                           MDI-X off

                             Status "connected"
SW-3560 <-----------------------------> SW-2960
speed auto                                                         speed auto <--- if set auto
duplex auto ("a-full")                                          duplex full <--- and set full
MDI-X on                                                           MDI-X off 

---

And what is the result if both sides are set to auto speed and auto duplex?

[ShoaibM]

Everything works fine if set to 'auto'. Duplex full, speed 100 on both sides.
Many thanks.