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Duplex setting on Trunk Ports

mcechman
Level 1
Level 1

Hello all -

I have two 3550's and I have trunking enabled on the fast ethernet ports. I have tried to set both ends to 100/full, however they do not come up. If I go back and set them both to auto/auto they come up. Can I not set trunk ports to 100/full?

Thanks,

Matt

6 Replies 6

Kevin Dorrell
Level 10
Level 10

Interesting. I don't see why not. Maybe it has some strange interaction with DTP. How are you forming your trunks, desirable-desirable, desirable-auto, or what? Did the ports come up in access mode, or did they not come up at all?

You could try debug dtp all

Kevin Dorrell

Luxembourg

They are desirable on both ends. If I do a debug dtp all, what would I be looking for? Trunk status?

Edison Ortiz
Hall of Fame
Hall of Fame

It sounds like you are using a straight-thru cable vs a cross-over cable. Once you configure the speed and duplex you are automatically disabling Auto-MDIX (http://www.cisco.com/en/US/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml#appc)

Change your cable to cross-over cable and then you should be able to change the speed and duplex.

HTH,

___

Edison.

Edison did they have auto-mdix back on the 3550's ? Not sure they did .

Glen, you are right.

glen.grant
VIP Alumni
VIP Alumni

I have never seen something like this . I would make sure the trunking parameters are exactly alike on both ends . Usuaully though you should get at least a link light , are the patches ok ? When you set it as auto does it autonegotiate 100/full ?

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