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?
 
Don JohnstonConnect With a Mentor InstructorCommented:
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
 
Don JohnstonConnect With a Mentor InstructorCommented:
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
Never miss a deadline with monday.com

The revolutionary project management tool is here!   Plan visually with a single glance and make sure your projects get done.

 
Craig BeckConnect With a Mentor Commented:
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
 
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
 
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
All Courses

From novice to tech pro — start learning today.