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210758 Views 22 Replies Latest reply: Feb 9, 2015 2:36 PM by Steven RSS 1 2 Previous Next

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Fa0/1 is up, line protocol is down (notconnect)

Jan 20, 2015 11:45 AM

markinu 10 posts since
Mar 3, 2009
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I am preparing for my ccent. After I read and revised the book I am going through questions.

I have this question where a switch connected to another switch displays ' Fa0/1 is up, line protocol is down (notconnect)'

when 'show interfaces fa0/1' is issued.

I thought only links between routers can have line 'up' and protocol 'down'.

Is there a mistake with the question, or I am missing something here?

  • Kerry LeBlanc 339 posts since
    Jul 29, 2008
    Currently Being Moderated
    1. Mar 12, 2009 6:35 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    My guess is that the port is configured for trunking, but trunking is not set up on the other end. Since you would normally only go switch to switch over a trunk line.

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  • Chris 811 posts since
    Jul 25, 2008
    Currently Being Moderated
    2. Mar 12, 2009 6:44 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

     

    Hi Markinu,

     

     

    You're correct. An switch port connected to another switch port should not have an Link "up" and Protocol "down", status.

     

     

    Is the question asking whether this state is possible?

     

     

    This is not a possible state on an L2 port connected to an L2 port.

     

     

    Could you type the question exactly as it is written.

     

     

     

     

     

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  • Chris 811 posts since
    Jul 25, 2008
    Currently Being Moderated
    5. Mar 12, 2009 7:51 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

     

    Yes. "Fastethernet 0/1 is up" means the same thing as Link/Line is "up".

     

     

    I'm still looking at the question though.

     

     

     

     

     

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  • Chris 811 posts since
    Jul 25, 2008
    Currently Being Moderated
    6. Mar 12, 2009 8:03 AM (in response to Chris)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    Well my answers to this question would be "B" and "C". However, the question is wrong concerning the line "up" and protocol "down" status. I'm also not sure as to why they have IP addresses assigned to physical switchports. Normally, on switches an IP is assigned to the "virtual" (interface vlan x) for remote management purposes. I think this question is very poorly written.

     

     

    Then, again because the topology doesn't show whether fa0/2 is the actual port on switch B maybe one shouldn't infer that, that is the interface referenced from switch B.

     

     

    Therefore, maybe "D" is correct because an IP should not be set on an physical switchport. An IP address cannot be assigned to an physical port on an switch because we're at L2, and L2 uses MAC addresses.

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  • Currently Being Moderated
    7. Mar 12, 2009 8:00 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

     

    I would say B and C would be the answers on that one. Basically having a direct Layer 2 connection between two switches you're operating with 2 layers that need to be up - the line and the protocols that run between the switches. Up/Down indicates that while the phsyical line is good - meaning you're seeing that there is a device connected at the other side - but it is not negotiating the link successfully.

     

     

     

     

     

    This could be caused by a unidirectional link of some type, a hardware/software failure on the switch, or the other side could be err-disabled or shutdown on the other side. This could also be a problem if different protocols are used for trunking(ISL vs dot1q).

     

     

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  • Mike.B 528 posts since
    Oct 20, 2008
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    8. Mar 12, 2009 8:02 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    I'll defer to the experts but B and C seem like reasonable answers (assuming that the cable is indeed connected to Fa0/2 on the other side...) B because we don't know what's configured on the other side (encapsulation, speed, duplex, etc) and C because the physical connectivity is up and the cable has been verified.

     

    -M

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  • Chris 811 posts since
    Jul 25, 2008
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    9. Mar 12, 2009 9:58 AM (in response to tnewshott)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    Hi Travis,

     

    I'm looking for more clarification.

     

    Here are my concerns:

     

     

     

     

     

     

    1.) I can buy the hardware/software failure.

     

     

     

     

     

     

    2.) If the other side were err-disabled, or shutdown the link/line wouldn't be in an "up" state at all...correct?

     

     

     

     

     

     

    3.) I can also buy the trunking encapsulation although that info wasn't given?

     

     

     

     

    Revised: Actually, having considered it further: I also believe you could have mismatched trunking protocols; or even one side configured as trunk, and the other as access, and the link would still be up; you just wouldn't be able to pass traffic. Please correct me if I'm wrong.

     

     

     

     

    Please understand I'm simply looking for clarification and I always appreciate your knowledge and assistance.

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  • Currently Being Moderated
    10. Mar 12, 2009 9:12 AM (in response to Chris)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    No offense taken at all. In theory, a port being shut down on the other side should not result in an up/down status - but I've seen just that before in production networks.

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  • Chris 811 posts since
    Jul 25, 2008
    Currently Being Moderated
    12. Mar 12, 2009 9:35 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

     

    Yes, you're correct mismatched trunking protocols does mean that one side is configured for ISL and the other side to dot1q. However, an mismatched setting would simply prevent an trunk from forming, or the passing of data across the trunk. However, the MAC-layer protocol of 802.3 or Ethernet II, which are basically the same thing, would still be in an "up" state.

     

     

    HTH

     

     

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  • Chris 811 posts since
    Jul 25, 2008
    Currently Being Moderated
    13. Mar 12, 2009 10:14 AM (in response to markinu)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    Also, if one side is set with: switchport mode access, and the other side set to switchport mode trunk; their Administrative and Operational Modes would be set to either static access or trunk, respectively. You're correct, they wouldn't be trunking and this is not an correct/viable configuration.

     

    HTH

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  • Currently Being Moderated
    14. Apr 15, 2010 6:51 PM (in response to Chris)
    Re: Fa0/1 is up, line protocol is down (notconnect)

    According to Wendell Odom this is not expected in a switch....?????? Could anyone clarify....?????? What does it mean by the interface is functional at Layer 1 OSI model

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