There are 2 options in using server & virtual server in GTM:
- Server is LB (uses Self IP), virtual servers are LB virtuals (virtuals IP/port).
- Server is standalone, virtual server is same server (same IP or secondary IP) + service port.
physical are used for virtual server discovery and monitoring.
When adding a LTM in GTM configuration, all virtual servers are automatically created in GTM. we can disable it if LTM virtual servers address are private and NAT is done by a firewall or router.
Physical server is also used to monitor virtual servers. instead of monitoring all virtual servers, LTM can provide all monitors to GTM in real time.
another goal of LTM servers is to probe LDNS from a datacenter without GTM:
In a deployment with more than 2 DC and with one LTM per DC, you can use only 1 GTM in 2 DC and use LTM in other DC to probe LDNS.