Forcing Speed Issues at C2960-C

[Saad Khalil]

Hi Everybody,

we have two Cisco C2960C (WS-C2960C-8PC-L) connected via Gig0/1 using Ethernet cooper cable, the issue here is when i force both interfaces to Speed 100 both interfaces tear down, 

any one have an explanation for such behavior, thanks to share it with us.

Switch 01 Interface configuration 

=========================

SW-01(config-if)#do show run inter gig0/1
Building configuration...

Current configuration : 87 bytes
!
interface GigabitEthernet0/1
switchport mode trunk
media-type rj45
speed 100
end

SW-01(config-if)#

// Interface State 

SW-01(config-if)#do show ip inter brie gig0/1
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/1 unassigned YES unset down down
SW-01(config-if)#

Switch 02 Interface configuration 

=========================

SW-02(config-if)#do show run inter gig0/1
Building configuration...

Current configuration : 87 bytes
!
interface GigabitEthernet0/1
switchport mode trunk
media-type rj45
speed 100
end

SW-02(config-if)#

// Interface State 

SW-02(config-if)#do show ip interface brief gig0/1
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/1 unassigned YES unset down down
SW-02(config-if)#

Thanks in advance

Saad

[Leo Laohoo]

---

@Saad Khalil wrote:

the issue here is when i force both interfaces to Speed 100 both interfaces tear down

---

Depends on the cable used.  When speed &/or duplex is hard coded, MDI/MDI-X is automatically disabled. 

FYI:  Hard-coding of speed/duplex is old school.  It WAS (past tense) best practice 20 years ago.  It is no longer recommended to hard code ports because it will only cause more issues and management.  

[Joseph W. Doherty]

Like Leo, I would also suspect you're disabling auto MDI/MDI-X.

[Saad Khalil]

thanks Joseph, is there any show command to verify that

[Joseph W. Doherty]

The auto-MDI/MDX setting might be shown in a show interface output, but unsure on that.

[Saad Khalil]

Thanks Leo for your reply, i know it is not recommended to do so it's just for testing the behavior.

[balaji.bandi]

adding to @Leo Laohoo  comments, what is the use case for make Gigabit port to megabit port ?

[Saad Khalil]

There is no specific case, i just need to test the behavior in case i have Giga Ethernet port connected to Fast Ethernet port.

[Joseph W. Doherty]

In that case, if the other side is auto, your gig port (if multi-speed copper) should auto neg. speed.

[balaji.bandi]

yes try set auto/auto both the side, assuming these switches in the same comms or server room ?