I recently joined a new company that uses the GTM or BigIP DNS. I am doing readings to understand the config. In one of the article (https://techdocs.f5.com/kb/en-us/products/big-ip_gtm/manuals/product/gtm-lb-configuring-11-6-0/2.html) that explains the order of preference, the GTM will first sort the topology records by the type of LDNS request source, then by the type of destination statement. What is a destination in the LDNS request? Isn't all DNS destination a record of some type (e.g. A, MX, TXT, ...etc)
For example, we have WIPs configured. They have pools that contain Virtual Servers... What is a destination type in this case?
An LDNS (Local Domain Name Server) defines the origin of a name resolution request (in other words, a DNS query). From a topology load balancing perspective, the characteristics of an LDNS can be used to direct a query from a particular source to a desired destination. Source characteristics include the LDNS' continent, country, ISP, IP subnet, region, state, or geolocation ISP. Based on these characteristics, a topology record can direct the request to a particular resource, including a continent, country, Data Center, ISP, IP subnet, pool of virtual servers, region, state, and geolocation. The goal is to respond to the query with a destination resource that makes the most sense given the query source.
You might try reading K13412: Overview of BIG-IP DNS Topology records (11.x - 14.x) for some more information. Also, you could refer to the Getting Started with BIG-IP DNS free training.