Q:  What is the license requirement for Link Load Balancing (LLB)?

A: No specific license is required. (Same license as that needed for LB). You need to have the load balancing feature enabled.

Q: What is resilient LLB?

A: Resilient LLB is the same as achieving redundancy. If one vserver, is down, we can direct traffic to another vserver (which acts as the backup). Thus we can configure backup virtual server. For more information refer to - http://docs.citrix.com/en-us/netscaler/10-5/ns-tmg-wrapper-10-con/ns-lb-wrapper-con-10/ns-lb-protect-wrapper-con/ns-lb-protect-config-backupvserver-tsk.html  

Q: Can source IP be implemented in the resilient LLB setup? 

A: Source IP cannot be implemented in resilient LLB setup. This is configured based on destination IP address (since we configure destination based routing). However,, if you want to implement this using source IP, you may implement Policy based routing (PBR). For more information refer to - http://support.citrix.com/article/CTX124716 

To know more about Link Load Balancing, refer to the following document:
http://docs.citrix.com/en-us/netscaler/10-5/ns-tmg-wrapper-10-con/ns-llb-gen-wrapper-10-con.html