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New Member

Speed/Duplex between two different switchs & SFP

Hi everybody,

I'm sorry about my poor english... I'm French (but it is not contagious)

I need your help (or TAC Help ) about speed and duplex problems.

My network :

[C2960G-24TC-L with sfp GLC-FE-100LX on Gig 0/23] <--> (Singlemode Fiber 9/125µ) <--> [Cisco SF200-24 with sfp MFELX1 on Gi1]

Autonegociation everywhere...

My problem :

%CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet0/23 (not full duplex), with f02929f97095 gi1 (full duplex).

- I can't force speed/duplex on MFELX1 (actually a-full a-100)

- I can't force speed/duplex on GLC-FE-100LX (actually a-half a-100)

Is there an incompatibility between this equipements ?

Configuration detail :

WS-C2960G-24TC-L   12.2(58)SE2           C2960-LANBASEK9-M

Cisco SF200-24 Firmware Version (Active Image):

#sh int gig 0/23 capabilities


  Model:                 WS-C2960G-24TC-L

  Type:                  100BaseLX-FE SFP

  Speed:                 100

  Duplex:                half,full

  Trunk encap. type:     802.1Q

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100)

  Flowcontrol:           rx-(off,on,desired),tx-(none)

  Fast Start:            yes

  QoS scheduling:        rx-(not configurable on per port basis),

                         tx-(4q3t) (3t: Two configurable values and one fixed.)

  CoS rewrite:           yes

  ToS rewrite:           yes

  UDLD:                  yes

  Inline power:          no

  SPAN:                  source/destination

  PortSecure:            yes

  Dot1x:                 yes

  Multiple Media Types:  rj45, sfp, auto-select

#show int gigabitEthernet 0/23 transceiver properties

Diagnostic Monitoring is not implemented.

Name : Gi0/23

Administrative Speed: auto

Administrative Duplex: auto

Administrative Auto-MDIX: on

Administrative Power Inline: N/A

Operational Speed: 100

Operational Duplex: half

Operational Auto-MDIX: on

Media Type: 100BaseLX-FE SFP

Configured Media: auto-select

Active Media: sfp

Thank you so much for yor help !

Hall of Fame Super Gold

Speed/Duplex between two different switchs & SFP

- I can't force speed/duplex on MFELX1 (actually a-full a-100)

- I can't force speed/duplex on GLC-FE-100LX (actually a-half a-100)

Disable interface CDP on both uplinks. 

New Member

Speed/Duplex between two different switchs & SFP

Thank you Leo,

It doesn't work, but I found an solution !

A strange solution...

I forced the C2960G-24TC-L to work with SFP :

media-type sfp

When I do that, I have the possibility to force the duplex (but not the speed... ok why not... ) :

duplex full

It is not very clean but my link is up and full-100 both sides.

Not very clean because :

C2960 side = force duplex, auto speed

SF200 side = auto duplex, auto speed

No errors... the link is clean.

Anyone known the reason or a better solution ?