FastEthernet0 is up, line protocol is down..Why?

janez_drk

Hope someone can help or explain to me this situation. To me this would be normal:

FastEthernet0 is up, line protocol is up: Both the Physical and Data Link layers on the interface are functioning correctly.
FastEthernet0 is down, line protocol is down: This output indicates a physical interface problem. For example, the cable on this interface or on the remote interface is disconnected.
FastEthernet0 is up, line protocol is down: In this case, Physical layer is operational. The line protocol being down indicates a clocking or framing problem. Probable reasons for this are encapsulation and clock rate mismatches.
Ethernet0 is administratively down, line protocol is down: This output indicates that a local interface has been manually shut down using the shutdown command.

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I have Cisco 1841 router and this is what is happening:
I configure the interface fa0/0 with IP address and no shut(the cable is not attached to this interface).
The interfece goes to up and up state...and after a while to protocol down state.

When I do show ip int brief I get this message:
FastEthernet0 is up, line protocol is down

I think that the message should be:
FastEthernet0 is down, line protocol is down
(no cable is attached to interface)

Will the interface go to down state, why is this happening?

Tnx

jahsoul

If possible could you throw the configs on here and what it is connected to. Do they share the same basic configs? (i.e. speed and duplex)

But from my limited knowledge-

1)Double check the cabling. I've had the problem were I assumed that it couldn't be a physical issue but it was.

2)Check speed and duplex settings

janez_drk

@jahsoul
Tnx for replay!
The thing is that there is no config ont the router.. It's my lab router..it has no startup-config..nothing at all..
Only thing that I do is:
conf t
int fa 0/0
no shut

the router shows me this massage: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up

and after when i do ''show ip int brief'':
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES unset up down


and the Status stays in ''up'' state - it won't go to down state

vinbuck

If I remember correctly, you can actually have an interface show as up even if all of the pairs aren't terminated properly in the Cat5/6 cable.

Check

1) Cabling - use a cable that is known to be working
2) Duplex - either Auto/Auto on both sides or hard coded for speed and duplex
3) IOS - are you using a stable IOS?
4) Change the device it is connected to on the other end to see if there is any change

advanex1

Agreed with what the others said. Check the cabling with a known good cable. Also, I'd double check to make sure you have correct encapsulation or clock rate as well.

janez_drk

As I said in my first post
I configure the interface fa0/0 with IP address and no shut(the cable is not attached to this interface).

So ther is no cable attached to the interface...I'm connected using console cable..

I have one brand new router..I will try that one..

here is something that I found

I don't think it's just Fast Ethernet. I've seen "Slow" Ethernet report
> > that the interface is up, down when nothing was attached. It seems to
just
> > be an indication that the interface passed a hardware check.


Re: FastEthernet is up, Line protocol down [7:1828]

billyr

There is nothing wrong with your router.

If you issue the No Shut command on your fast ethernet interface even when no cable is attached it will show as: Up Down

Most books will tell you it should say: Down Down, but as you've just found out in real life (not a simulator) it doesn't. However if you repeat the same No shut command on a serial interface it with no cable attached it will show as Down Down.

janez_drk

The same thing happens with the brand new router...out of the box..

Thanks for the replays..

wallpaper_01

Sorry to bring this back up but why does it show up/down with ethernet but down/down with serial?

How would you troubleshoot a bad ethernet cable if it shows up when no cable is even connected?

FloOz

If the other end of the cat cable is not attached to an interface you can do a no keepalive cmd on fa0/0 and the interface will then show as up/up

wallpaper_01

I understand that, but that still doesn't explain the difference between serial and ethernet down/down and up/down status difference or how to know if an ethernet cable is faulty.

Does serial work differently requiring a keepalive for the other device but ethernet doesnt?