What is the difference between GTM and the Load Balancer?

Short answer

Load Balancer - ADC receives the client's connection on the vService and distributes the traffic to the healthy Backend Services within a data center; the traffic flows through TR7. GTM, on the other hand, does not carry the traffic: it answers the DNS query and tells the client, before the connection is established, which address, and therefore which data center, to go to. The Load Balancer decides within a data center, and GTM between data centers; when they are used together, the address that GTM returns is usually the vService address in each data center. The two products are licensed separately (Products & Licensing).

How Does It Work?

1. The client asks for the domain name; the query comes to GTM through the resolver, and GTM returns a healthy and suitable address.
2. The client connects to this address. If the address is a vService, the connection is received by the Load Balancer in that data center.
3. The Load Balancer forwards the request to a Backend Service according to the Algorithm and the health check results.

GTM's decision is made in step 1, and the Load Balancer's decision in step 3. For choosing a product: What is the difference between Load Balancer and GTM; which one should I use?

Comparison

	Load Balancer - ADC	GTM
Layer it works at	Connection and application (L4–L7)	DNS
Decision moment	After the connection is established, on each connection or request	Before the connection, in the DNS query
Scope	Servers within a data center	Across data centers and regions
Does the traffic pass through TR7?	Yes	No; only the DNS answer is given
Health information	Health check profiles bound to the Backend Services	GTM's own Health Checks and Health Scenarios definitions, Remote Devices metrics
When the decision takes effect	Immediately on new connections	After the TTL period of the previous answer expires
Product	TR7 ADC	TR7 GTM

GTM and the Load Balancer in TR7

• The Load Balancer is managed from the Load Balancer tab of the Configuration Menu, and GTM from the GTM tab.
• GTM's DNS Service also listens on a Frontend IP and Port; if the same address and port are used by a vService, the Port collision warning is given in the form.
• In Datacenter mode, GTM can also sort the data centers according to the metrics of a vService there (How are GTM and the Load Balancer used together?).

Common Misconceptions

• "GTM takes the place of the Load Balancer." GTM tells only which address to go to; TLS termination, content routing and distribution to the Backend Services are the job of the Load Balancer.
• "When a data center goes down, GTM moves the open connections to the other one." GTM changes only the new DNS answers; clients go to the new address when the cached answer expires and they query again.
• "GTM uses the health checks of the Load Balancer." GTM works with its own Health Checks definitions; it reads the vService Status with the Datacenter HC type.

How it is done in the documentation

• GTM (Global Traffic Manager) · Its Difference From Local Load Balancing
• Load Balancer - ADC · Difference from GTM
• Products & Licensing · Products

Related questions

• What is GTM (Global Traffic Manager) and what does it do?
• How are GTM and the Load Balancer used together?
• What is the difference between Load Balancer and GTM; which one should I use?
• For redundancy across data centers, should I use Load Balancer or GTM?