What is a DNS Service in GTM?

Short answer

DNS Service is GTM's authoritative listener that serves queries: it receives DNS queries over UDP and TCP on the defined Frontend IP addresses and ports (default 53) and produces answers for the domains it hosts. All domains and records are bound to a service; on a single TR7, multiple services work side by side, each with its own addresses, cache and resource limits. Services are created on the Configuration Menu → GTM → GTM Services → Service Management screen.

How Does It Work?

1. The service waits for queries on every address and port in the Frontend IP table; a service with no address defined does not serve queries.
2. If the queried name belongs to one of the service's domains, the service produces the answer from the records.
3. If the name is outside the service's domains and a DNS Forwarder profile is assigned to the service, the query is forwarded to the upstream servers in the profile; if no profile is assigned, the query is not resolved.
4. If Cache is on, repeated queries are answered from the cache. If Log is on, incoming queries are written to the service's own log.

DNS Service in TR7

Field	What it determines
DNS Service Name	The name of the service shown in the menu, in the Left Monitor Panel and in the logs
Route Table	Which addresses are offered in the Frontend IP list (default DEFAULT)
Frontend IP and Port	The addresses on which queries are listened for; more than one row can be added
DNS Forwarder	The forwarder profile for the queries for which the service is not authoritative; while it is on, the DIRECT option appears per address
Cache	The cache; while it is on, Cache TTL (default 60 seconds) and Max. Cache Entries (default 1,000,000)
QOS	Cores, processor priority, processor and memory limits
Log	DNS query logging

The status of the service is shown in the list and in the preview with the status values: OK (working), Error (present but not working), Absent (not created yet), Forwarder error / Forwarder absent (the service is working, the bound forwarder is not working or has not been created), Host is off (no connection with the device). Domains and records are tracked on the Domains and Records tabs of the service's own screen, and the service's traffic on the Dashboard tab. In a cluster, the service definition is also transferred to the peer device.

Common Misconceptions

• "Deleting the service deletes only the service." When the service is deleted, all of its domains and records are deleted with it.
• "When Log is turned on, the queries appear on the GTM Logs screen." The query lines are written to the service's own log; the GTM Logs screen shows the service's GTM events and user operations (Can GTM log DNS queries; where are the logs shown?).
• "Restart Service restarts the service on both cluster devices at once." Restart Service in the preview restarts the service only on the device the interface is connected to.

How it is done in the documentation

• Service Management · What Is a DNS Service?
• Service Management · DNS Service Add Form
• Service Management · The Status Values
• Service Management · Operating Mechanism

Related questions

• What is a domain in GTM; how does it relate to a DNS Service?
• What is the DNS Forwarder; what happens to queries GTM is not authoritative for?
• What are the basic building blocks of GTM?
• Which monitoring screens does GTM have; what does each one show?