ccna 1 exam 7

ccna 1 exam 7.Periodic survive messages keep the link UP, otherwise the link fails. In particular, after a router does not receive a survivor message from another router for a certain survivor interval (3 to 5 intervals by default, depending on the IOS version), that router shuts down the interface and considers this pickup from the other router to be no longer working.The link will work as long as both routers use surviving messages, or both disable surviving messages. However, if one end enables and the other disables the surviving message, an error occurs. This error only disrupts the HDLC link; the PPP live feature prevents this error, and Figure 12-17 shows an example of HDLC where R1 incorrectly disables live messages.interface serial 0/0/0 interface serial 0/0/1encapsulation hdlc no keepalive encapsulation hdlc192 168 2 2---g---1 S0/0/1 - ___ S0/0/1-R2 -Line : Up Line : UpProtocol : Up Protocol : DownFigure 12-17 Errors that Cause Down/down Problems on Router R2 In the Figure 2-17 scenario. the R2 interface fails because: R1 is not sending a survivor message because survivorship is disabled.. and R2's waiting to receive a live message because R2 has enabled live messages. After failing to listen for a surviving message (default is 3 surviving intervals), R2 puts the link in the up/down state. Over time, R2 may place the link in the up/up state, and then after more than 3 survival intervals, the interface returns to the up/down state. Example 12-6 shows how to find evidence of a survivorship mismatch. First, it gives the command showinterfacesS0/0/0 executed on R1