HI,
Thats the problem with NAT TCP load balancing. Router will still try to send the Nth connection (on round robin basis) to a particular server and if that server fails, it will still send the connection to taht server and connection will fail.
Cisco Local Director helps in preventing this problem. It keeps track of which servers are active and which are not, using a keepalive mechanism and hence connections wont fail.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus