GTM VS DNS server

Complementing what Kevin wrote, with BIG-IP DNS you have the same benefits of the traditional DNS and much more in terms of availability, performance, security and management capabilities:

Traditional DNS (BIND & Microsoft DNS):

• Do not offers GSLB capabilities.
• Do not offers true high availability. (There's no monitors)
• They only have a limited possibility of static load balancing. (Ex. Round Robin).
• You could have potential errors when editing DNS files using BIND, without validation.
• Performance is slower, because the resolution process tipically is done reading your records from the HDD.

F5 BIG-IP DNS:

• Offer Full GSLB capabilities.
• Offer True High Availability (HA). You could monitor every resource in every Data Center and only resolve to working addresses.
• You have static and dynamic load balancing capabilities in order to resolve to best of available addresses (Ex. QoS, Topology, Least Connection LB methods).
• There's a great tool (Zonerunner) for editing address records, that validates your input.
• Performance is faster, because the resolution process tipically is done reading your records from the RAM (DNS Express).
• DDoS protection.
• Easier configuration for DNSSEC (All-in-One).
• F5 Analytics visibility that provide information about your resolutions. (Top Countries, Top domains, etc.)