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New Member

Fa0/0 line up, protocol down


On a 3745, IOS 12.3(9), (fc2), sh int produces "FastEthernet0/0 is up, line protocol is down", even if the network cable is disconnected.

I thought the Fa0/0 state would always be down if the cable is disconnected. Does the Up/Down state tell me something important?

(The real problem, of course, is that the line state remains Up/Down even with the cable connected. I've checked over and over to make sure the switchport it's connected to is in the right vlan for the assigned IP address, and checked our other 3745 (on which both Fa ports work fine) for any config difference, all to no avail. Then noticed the Up/Down state, and thought maybe someone knows what condition that indicates...)




Re: Fa0/0 line up, protocol down


Can u plz try this.

check the speed/duplex settings

check weather the cable is in a good condition

check weather it is properly terminated.



New Member

Re: Fa0/0 line up, protocol down

Hi Mahmood,

Thanks - I'm guessing that will do it - So simple, and I checked the router side port, but neglected to check the switch side port. (Yeesh, what I newbie I am!)

I'll check in the morning - will flag this as a solution if it works...


Re: Fa0/0 line up, protocol down


"FastEthernet0/0 is up, line protocol is down". This means that the port is administratively up( means no shut command has been issued), but the line protocol is down either because the cable is not connected, the port on the other end is shut, or maybe if the ports are on auto-neogtiate the negotiation has failed.

Now onto your "real" problem,the line protocol is down even when a cable is connected then either the cable if faulty, try changing the cable. If that doesnt help then try hard-coding the ports.

Hope that helps.



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New Member

Re: Fa0/0 line up, protocol down

Thanks for your responses - I have learned 2 things thereby.

1. Apparently Fa ports act a little differently on switches than they do on routers. I double-checked today - on my 3550 switches, Fa ports with no connected device are "line down/protocol down", even if they are not administratively shutdown.

2. Gig ports on gig modules are 1 speed - no auto negotiate, and no setting them to speed 100.

Hope this turns out useful info to others...


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