Cisco Software Developer Engineer interview questions

Apllied through my friend's friend who is an employee of Cisco. The interview was with three people one-to-one, each averages 45 mins. They needed somebody with expertise in OS, device drivers and C. Most of the questions were from what we find on internet, the standard questions including C programs. Lack of preparation cost me.

Basic C questions (Pointer,Structures,linked list, arrays,data types), Computer Networking concepts (TCP/IP,UDP). I was interviewed for 1 hour. It was pretty simple. Though I screwed up in some of them. I could not answer most efficient way in finding number of 1's in a given number.