Interface Status UP, Protocol UP

I wonder in which case we can see Interface Status UP, Protocol UP even when  nothing plugged in

Thank you
jskfanAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Don JohnstonInstructorCommented:
I've never seen that on a physical interface.  Unless you did something like loop the interface.
0
jskfanAuthor Commented:
I have just tested it.

if you turn keep alive off on an interface (not loopback interface), you will not be able to ping after the keep alive period expires. however if you run show ip interface brief , the interface will still show the Status is UP and the Protocol is UP.
0
Craig BeckCommented:
The keepalive tells the port whether to monitor the link-state or not.  If you issue the no keepalive command on a FastEthernet interface, for example, the status will go UP/UP.
if you turn keep alive off on an interface (not loopback interface), you will not be able to ping after the keep alive period expires.
Kind of...

Once you disable keepalives on an interface there is no keepalive timer, so the interface should stay up indefinitely.  If you assign an IP address to an Ethernet interface it will always be UP/UP so it will always be pingable if a packet is routed to it from another interface.  However, if you do this with an SVI it might behave differently depending on the hardware platform.

It doesn't work on all interfaces though in my experience... serial interfaces, for example, won't do this.
0
Ultimate Tool Kit for Technology Solution Provider

Broken down into practical pointers and step-by-step instructions, the IT Service Excellence Tool Kit delivers expert advice for technology solution providers. Get your free copy now.

jskfanAuthor Commented:
On R1  I issued no keep alive command, then I shut down the interface connecting R1 to R2, the Shut Down command was typed only on R1.
I issued ping command from R2 to R1, I got ping reply from R1 for few times , then could not ping it, I guess the keep alive period expired.

On R1 , I issued the command : show ip interface brief ,  on the interface I shut down , I still I can see the status UP and protocol UP.
0
Don JohnstonInstructorCommented:
If the interface is shut down, it should not show as UP/UP. It should show "Administratively Down".

Is this a real router or a simulator?
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
jskfanAuthor Commented:
This is GNS 3
0
jskfanAuthor Commented:
real IOS though
0
Craig BeckCommented:
GNS is a bit different at some things. I'd test that with real kit.
0
jskfanAuthor Commented:
Thank you
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Routers

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.