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The Cisco IOS v1.22 – Aaron Balchunas

* * *

Aaron Balchunas (aaron@routeralley.com),

This material may be copied and used freely, but may not be altered or sold without the expressed written

consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.

Status of Router Interfaces (continued)

Traffic can only be routed across an interface if its status is as follows:

Serial 0 is up, line protocol is up

The first part of this status (Serial0 is up) refers to the physical layer status

of the interface. The second part (line protocol is up) refers to the data-link

layer status of the interface. A status of up/up indicates that the physical

interface is active, and both sending and receiving keepalives.

An interface that is physically down will display the following status:

Serial 0 is down, line protocol is down

The mostly likely cause of the above status is a defective (or unplugged)

cable or interface.

There are several potential causes of the following status:

Serial 0 is up, line protocol is down

Recall that line protocol refers to data-link layer functions. Potential causes

of the above status could include:

• Absence of keepalives being sent or received

• Clock rate not set on the DCE side of a serial connection

• Different encapsulation types set on either side of the link

An interface that has been administratively shutdown will display the

following status:

Serial 0 is administratively down, line protocol is down

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Cisco IOS Router Manual do Utilizador Página 13