LInk Controller Mail domain delegation

In your example above I´m missing the trailing dots behind images.example.com.

Imho it should read:

images.example.com.     IN  NS  lc1
images.example.com.     IN  NS  lc2

A delegation on your authoritative name server may look like this:

subdomain.f5test.local. IN   NS     lc_isp1.f5test.local.
subdomain.f5test.local. IN   NS     lc_isp2.f5test.local.
lc_isp1.f5test.local.   IN   A      10.1.0.253
lc_isp2.f5test.local.   IN   A      10.2.0.253
www.f5test.local.       IN   CNAME  www.subdomain.f5test.local.

Both specified link controller interfaces are treated as authoritative for the subdomain.

The link controller will be able to resolve www.subdomain.f5test.local to A records associated with virtual servers on your link controller.

To accomplish this you will need 2 virtual servers (one per ISP link) which will be assigned to the so called Wide IP on the link controller.

The virtual servers are bound to a local pool of servers (subset of LTM feature).