Dear Reza,

please forget about tracking..my main query is why fastethernet/ethernet interfaces showing UP and UP status only when link gone down and why serial interfaces showing UP and DOWN when link gone down?

Thanks and Regards,

sourabh

sourabh

One part of the explanation of the different behavior between Ethernet/FastEthernet and serial interfaces is that the serial interfaces use a keepalive mechanism that sends keepalive packets over the serial interface and must receive keepalive packets over the serial interface. If the correct keepalives are not received then the serial interface shows up and down. The keepalive on the Ethernet/FastEthernet does not work quite the same way and so the behavior is different.

Another part of the explanation is that while the serial keepalive works end to end over the link the Ethernet/FastEthernet does not check end to end (from router to router or whatever is connected on the Ethernet). The Ethernet/FastEthernet only checks to the next connected device which is usually a switch. So your router Ethernet/FastEthernet will report up and up because it is connected to a switch which is working and does not detect that the router on the other end of the link is down.

HTH

Rick

thanks a lot for your great answer...