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To me if you don't configure all of your Citrix Web Interfaces (WI) to use a network load balance (NLB) setup you are asking for trouble as you have now created a single point of failure within your environment!
NLB is available in Windows Server 2008 standard and enterprise so you should now have no excuses to implement this in to your environment.
First thing First lets configure 2 Windows 2008 R2 server with NLB, in my test environment the two servers are XenApp.ctxlab.com (192.168.219.129) and XenApp2.ctxlab.com (192.168.219.131) and the NLB address will be XANLB.ctxlab.com (192.168.219.135).
1. Install the Network Load Balancing feature on both servers that will be hosting both the WI.
2. Once NLB is installed start the NLB manager and right click to create new cluster.
3. Enter the first member in the NLB cluster and click Connect and the Next
4. Check that the IP address is correct and put a tick in the retain suspended state (to help avoid a webserver kicking in after rebooting during controlled maintenance) and click next.
5. Enter the clusters IP address and Subnet Mask and click on OK.
6. Add in the FQDN of the cluster and change the Cluster mode to Multicast.
7. Click on edit to the current port.
8. Change the port range to 80-80 and the protocol to TCP
9. Once the port is changed click on finish.
10. You should now see the first member of the cluster added correctly and add the other member of the cluster. I wont give a description of each point here as this is done in nearly the exact same way as above I'd add the screenshots to help if anyone gets stuck.
11. Once you have added the second member to the cluster you should now see both members working correctly.