If you have multiple sites or hostnames off one IP, you will want to get a health check on each site so you can see if one site is having problems over another. To do this, create a SubVS for each site and also content matching rules for each hostname.'
To begin, create two content rules to match two different hostnames; site1.com and site2.com. Rules & Checking > Content Rules.
Now, create the VS with two SubVS, one SubVS for each respective site. 1. Enable Content Switching inside the parent VS under Advanced Properties.
2. Assign the rules you just created to each SubVS. For each site you must click “none” then assign the proper content rule to it.'
For each SubVS, specify hostnames within the Real Server check parameters. Check HTTP/1.1 Host. After this is done, specify a host header to be sent to the real server.
The LM sends this hostname to the real server for the healthchecks. Verify this is the request using a packet capture.
This is also reflected on view/modify services tab where both SubVSs show as green and up.