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as u said the loopback is used for determine the designated router in the ospf routing process
as u know the designated router is the router which has the hieghest ip or its the router which has a higher loopback
ip.
cisco advice u if u need to make an election for the designated router to implement a loopback interface to the router and assign it an ip
but why we use the loopback interface rather than the physical interface in the election process for the designated router
the answer is so easy
because the physical interface may be shutdown and become inactive for any disaster reason
but
the loopback is always active because its logical interface
so as the rourter is on as the loopback is on too .
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we can also use the loopback interfcae for implement
an access server router where we can control many routers by using a server router to control or configure all of them
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we can use the loopback also as atest for connectivity in wan routing and in ethernet interface also
whether in ( isdn - atm - framrealy - so on)
and there many methods to applay that kind of test
any way there is many article by cisco in how to use the loop back kinds
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:comp21: to be honest with you i am still discover every day
alot of benefits by this loopback interfcae. its
the magic key for alot of usage whether in cisco
or microsoft .
best wishes
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