how does he finally get his revenge on Lip-lip?

White Fang finally gets his revenge by luring Lip-lip into close range of Kiche.

He attacks Lip-lip and kills him.

From the text:

"White Fang struck him hard, shoulder to shoulder. Lip-lip was overthrown

and rolled upon his back. White Fang's teeth drove into the scrawmy throat. There was a death-struggle, during which White Fang walked around, stiff-legged

and observant. Then he resumed his course and trotted on along the base of the bluff.

Note: White Fang's revenge is eliminating Lip-lip.