Protocol Status refers generally two the layer to status. It is always down if the Line status is down. if the Line status is up,a protocol status of down usually is caused by mismatched data link layer configuration
For an example serial interfaces has their combination when one router has configured to use PPP(Point_to_Point Protocol) and other remains the default HDLC (Higher_level Data Link Control) configuration and this will cause to display as "Line status Up Protocol Down" .
- Before Configure one router to PPP (Default is HDLC)
R1#show interfaces serial 1/0
Serial1/0 is up, line protocol is up (connected)
Hardware is HD64570
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
R2#show interfaces se1/0
****Serial1/0 is up, line protocol is up** (connected)**
Hardware is HD64570
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
- After configuring R1 as PPP
R1#show interfaces serial 1/0
Serial1/0 is up, line protocol is down (disabled)
Hardware is HD64570
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
R2#show interfaces serial 1/0
Serial1/0 is up, line protocol is down (disabled)
Hardware is HD64570
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
1Please consider accepting answers on your previous questions which have helped/solved your problem. That'll mark the question as solved in the system. You can accept an answer by clicking on the checkbox next to the answer you want to accept – Sathyajith Bhat – 2011-09-21T11:05:49.260