FastEthernet0/1 is up, line protocol is up

[SJ K]

Hi guys,

I know this is old question and have found several in the forum. But what does

the 1st up means ? and the 2nd up means ?

On the book, it says 1st up = physical layer ok = receive carrier detect

                                 2nd up = data layer ok = keepalives recieved

q1) is gurus here able to elaborate abit further on "carrier detect" and "keep alive"

- does it means that if I have a physical link plug in correctly to both side, I will have carrier detect ?

q2) I am using GNS now and my fe0/1 on both router have no physical link at all.  Furthermore only 1 interface is set with IP. but I still get both up. Why ?

R1

FastEthernet0/1 is up, line protocol is up
  Hardware is Gt96k FE, address is c200.276c.0001 (bia c200.276c.0001)
  Internet address is 192.168.10.1/24
  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255


R2

FastEthernet0/1 is up, line protocol is up
  Hardware is Gt96k FE, address is c202.276c.0001 (bia c202.276c.0001)
  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255

Regards,

Noob

[Leo Laohoo]

FastEthernet0/1 is up

Means Layer 1. 

line protocol is up

Means Layer 2.  

[SJ K]

Hi Leo,

Thanks for reverting.

Layer 1 up as in just the interface itself is up is sufficient (e.g. i issue no shut on the interface) , is it consider as layer 1 up already ? or the cabling connection must be there ?

Layer 2 up - is auto/duplex/speed negotiation etc consider L2 or L1 ?
Layer 2 - does it also check VLAN settings or anything ?

Regards,
Noob
 

[Leo Laohoo]

is it consider as layer 1 up already ?

Layer 1 is up, generally speaking. 

or the cabling connection must be there ?

Yes.  

Layer 2 up - is auto/duplex/speed negotiation etc consider L2 or L1 ? 

Speed and duplex are shown a few lines down.

Layer 2 - does it also check VLAN settings or anything 

No.  

[SJ K]

Hi Leo,

Thanks for coming back.

I am sorry to be naggy but when you mention yes to both just up the interface without the cable connection and with cable connection on q1)

q1) what will be the actual situation if i have up an interface but without any physical cable connection. Will it show FastEthernet0/1 is up ?  (sorry i really dont have a lab to test except on my GNS)

q2) when you mention Line protocol is up = Layer 2 is up = what does it actually check ? is speed and duplex setting part of the check ?  (you mentioned they are shown a few lines down, but i am not sure are those consider as Layer 1 checks or Layer 2 checks )

Thanks!

[devils_advocate]

If a cable is not plugged in, you will see Down Down for both L1 and L2.


 

[SJ K]

Hi all,

Using GNS , i have setup a router as a standalone, issue no shut to an interface and both is showing up.
 

I guess thats a GNS flaw or bug, is it ?

Regards,
Noob

[devils_advocate]

Yes that sounds like it could be a bug. 

[Leo Laohoo]

q1) what will be the actual situation if i have up an interface but without any physical cable connection. Will it show FastEthernet0/1 is up ?  (sorry i really dont have a lab to test except on my GNS)

It'll show up as down/down because there is no Layer 1 active.

[SJ K]

Dear all,

Sorry to trouble, is it possible to list 1 highly possible scenario whereby L1 is up and L2 is down ?

(such as .e.g cable is connected to both switches/routers but ... ?)

Regards,

Noob