Can someone explain how unicast RPF or RPF works in ASA?

I have really hard time understanding RPF in cisco asa packet flow and how it contains spoofing or dos attacks ?

Hello Harshi

Unicast RPF can be reviewed in general at this lesson:

Now specifically for uRPF in the ASA, take a look at this Cisco document that describes its functionality for both IOS and ASA devices:

I hope this has been helpful!