Using a GTM without an LTM
We've been using a BIG-IP LTM for a while now in a design that utilizes both SNAT and DNAT. Customers who maintain the server logs have been complaining that we're not leaving the srcIP of the session intact, so while we'd debated using the different LTM designs (where the LTM is the default gateway for the backend servers, etc), the solution we decided on was to use the DNS load-balancing found within the GTM. In other words, we have an LTM that's also a GTM, but we want to separate the duties of the two, if possible. The LTM will handle situations where the srcIP doesn't need to be maintained, and the GTM will handle everything else. Basically, we have a GTM for its DNS capabilities - within one datacenter with one LTM.
Fast-forward to configuration of the GTM. It's up and running, responding to DNS like I expect, but I'm struggling with monitoring real servers. In essence, neither my GTM "server" nor my GTM "pool" seems to have the ability to monitor (for example) tcp/514 to determine if that port is running and, therefore, the GTM should continue to keep that real server in the pool. Basically, I'm looking for the server/pool monitoring functionality from the LTM in the GTM. Is this possible? Or, do I need to create a VIP for each real server in my LTM and monitor the real servers there? Or is there another way to open a tcp session to a specific port within GTM to determine if a single real server should be in the GTM pool?