Cisco 3825 Gigabit Interface does not connect when set to 100/FDX

Unanswered Question
Feb 2nd, 2007

Customer originally had a Cisco 2621XM whose Fast Ethernet Port was connected to a Catalyst 2950 and both ends set to 100/FDX and everything was working fine. Today customer replaced Cisco 2621XM to a Cisco 3825. When 3825 and 2950 are set to Auto the Link comes up OK and everything works fine. When set to 100/FDX at both ends the link stays down.

Customer is not happy even then. He wants the link to come up when 3825 Gi0/0 and 2950 port are both hard-coded for 100/FDX.

I have this problem too.
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astanislaus Fri, 02/02/2007 - 01:42

Please note:

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1. Interface Gi0/0 of the 3825 is currently connected to our upstream internet provider's switch (manufacturer unknown, but they advise me it's a gigabit interface which is currently forced to 100Mbps/FDX (both ends are forced to 100/FDX)). Interface Gi0/1 of the 3825 is currently connected to interface FE0/6 of 2950-24 node DMZGwnSX001 (both ends are set to auto-neg and are operating normally - no errors).

During the testing, Interface Gi0/1 on the 3825 was connected to Interface FE0/24 on the 2950T-24 and both were configured for 802.1q encapsulation carrying VLAN's 60 and 61. Both interfaces were forced to 100Mbps/FDX which resulted in a linkdown status.

Please note the show tech from the 2950T-24 does not reflect the interface and VLAN configuration used during the test as it has since been reconfigured.

glen.grant Fri, 02/02/2007 - 04:53

Check to see if the 3825 port has auto mdix turned on , if so then it has to be auto for it to work or turn auto mdix off and you should be able to hardcode .

astanislaus Fri, 02/02/2007 - 05:01

Auto MDIX - Is this an Interface Configuration Command? I will check out the syntax when I log into the router.

astanislaus Fri, 02/02/2007 - 05:02

Auto MDIX - Is this an Interface Configuration Command? I will check out the syntax when I log into the router.

glen.grant Fri, 02/02/2007 - 05:17

Yes it is , though I am not positive if that is supported on the that model or not . See if it will accept "no mdix auto" on the interface , if not it is not relevant .

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