What determines status in Protocol when using command show ip interface bri?

[wfqk]

In Cisco device router or switch, when we use command show ip interface bri, we can see column of Status and Protocol for the interface. We know command shutdown determine the Status of the interface --- up or administratively down, but the Protocol column could be determined by several factors, such as other end status etc. However, in some situation, the Protocol status is always up no matter if other end status. Any one can give some explanation? Thank you

R4(config-if)#do sh ip int bri

Interface             IP-Address            OK?    Method     Status                               Protocol

Ethernet1/0        34.1.1.4                 YES    NVRAM    up                                      up
Ethernet1/1        34.1.2.4                 YES    NVRAM    up                                      up
Ethernet1/2        unassigned           YES     NVRAM    administratively down       down
Ethernet1/3        unassigned           YES     NVRAM    administratively down       down

[Richard Burts]

In most cases the protocol status reflects the processing of keepalive messages. If keepalives are sent and are received then the protocol status is UP and if keepalives are not sent or not received then the protocol status is DOWN.

HTH

Rick

[wfqk]

Thanks for your reply. It looks like that protocol status for ethernet is up even if other end is shutdown. but serial interface is not up. Do you think so? 

[Richard Burts · Accepted solution]

You are correct that in general for Ethernet the protocol state is not dependent on the other end and in many serial interfaces the protocol state is dependent on the other end. Part of the reason for this is that for many of the serial protocols the keepalive process is that you generate a keepalive and send it to the other end and the other end sends it back to you for a successful keepalive.

HTH

Rick