I'm supporting an IIS based application that is scaled out into web and application servers. Both web and applications run behind IIS. The application is NTLM capable when IIS is configured to authenticate via Kerberos. It's been working so far without a glitch.

Now, I'm trying to bring in 2 F5 switches, 1 in front of the web and another in front of the application servers. 2 F5 instances (say ips 185 & 186) are sitting on a LINUX host. F5 to F5 looks for a NAT IP (say ips 194, 195 and 196). Created a DNS entry for all IPs including NAT and ran a SETSPN command to register the IIS service account to be trusted at HTTP, HOST and domain level. With the Web F5 turned on and with eachweb server connecting to a cardinal app server, when the user connects to the Web F5 domain name, trust works and user authenticates without a problem. However, when app load balancer is turned on and web servers are pointed to the new F5 app domain name, user gets 401. IIS log shows no authenticated username and shows a 401 status. Wireshark does show negotiate ticket header passed into the system.

Any ideas or suggestions are much appreciated. Please advice.