What is the use of loopback???

What is the use of loopback, I knowthat it is always up and never goes down. What else? can you give me an idea.

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One use of the loopback interface is to make it the Router ID.This can help you if you have to troubleshoot a network problem because if you assign router id's manually you will know what router originated what LSA.
The stability factor doesnt really count with Cisco because you can delete the interface which corresponds to the router id but still this address will stay in the system as the router id.In other vendors equipment however if an interface resets this can effect the router id and hence a flooding of lsa's would result due to a downed interface.
So in Cisco a loopback interface is just handy to use and good practice.
Anyway im not sure if you will get wht i mean,u will if you understand ospf.If not do a search because this question has benn asked many times.

chinaman

Don't worry your explanation is clear and I got what you mean. When I followed the sybex 5th edition chapter 6 ospf that ospf wil advertise this RID and also used to elect a DR and BDR.

And if my int goes down , re-election again and a FLOOD on my netwrk.

Am i correct, it is like your giving a Virtual ID in a physical int.