What is DNS; where is it used in TR7?

Short answer

DNS (Domain Name System) is the distributed name resolution system that translates domain names into IP addresses (and vice versa) (RFC 1034); before going to the www.example.com address, the browser asks DNS which IP this name corresponds to. In TR7, DNS is used in two directions. When the device itself needs to resolve a name (e.g. when a Backend Service is defined with a domain name instead of an IP), it uses the DNS Servers list entered per route table on the Device DNS screen. GTM, on the other hand, turns TR7 into an authoritative DNS server that answers for its own domains: a DNS Service is defined, Domains and Records are added, and the answers are determined according to the health status of the records.

Where It Is Used in TR7

Where	Field / label	What for
Settings → General Settings → Device DNS	DNS Servers, Virtual Hosts (for the selected Route Table)	The DNS servers that TR7 will use in its own name resolution and the static name → IP records
Load Balancer → Backend Services	A domain name (FQDN) instead of an IP in the Address field	Defining the Backend Service with a domain name; if the name cannot be resolved, DNS Resolution Error appears in the vService preview; the domain name is resolved once when the configuration is applied, and if the DNS record changes later, the new address is not used until the configuration is applied again
GTM → GTM Services → Service Management	DNS Service	TR7 listening as an authoritative DNS server for domains (default port 53)
GTM → GTM Services → service name → Domains / Records	Domains, Records	Managing zones and DNS records
GTM → DNS Forwarder Profiles	DNS Forwarder Profiles	Forwarding the queries for which the DNS service is not authoritative to upstream DNS servers
Load Balancer → Profiles → Health Checks; GTM → Health Checks	Check Type = DNS (DNS in GTM)	Checking whether DNS servers respond
Certificates & PKI → ACME DNS Providers	ACME DNS Providers	The API information of the DNS provider for ACME DNS-01 validation
Bot/DDoS → L4 DDoS Protection → route table → UDP flood	DNS Flood	The per-second DNS request limit per source IP

The Two Directions of DNS in TR7

	Device DNS	GTM
TR7's role	DNS client: asks the question	DNS server: answers the question
Whose question	TR7's own operations (Backend Service domain name, notification and log servers, license and update access)	The questions of clients and other DNS servers
Scope	Per route table; each route table carries its own list	Per DNS service; each service carries its own domains and records
Cluster	The settings are synchronized to the peer device automatically	The definitions are reflected to the peer device; each device calculates its answer itself

• The difference between an authoritative server and a resolver: What is the difference between an authoritative DNS server and a recursive resolver?
• DNS queries are mostly carried over UDP, and over TCP for large responses and in zone transfers; the GTM DNS service accepts queries over both protocols (What is UDP; how does it differ from TCP?).

Common Misconceptions

• "GTM and Device DNS are the same setting." Device DNS determines whom TR7 asks its own questions; GTM, on the other hand, is TR7 answering the questions of others. Each one works without the other.
• "Device DNS is common to all route tables." Each route table carries its own DNS servers list; it is not inherited from the default route table.
• "DNS is only for websites." Many operations, such as e-mail (MX), service discovery (SRV) and the permission to issue certificates (CAA), also rely on DNS records.

How it is done in the documentation

• Device DNS · What Is Device DNS?
• Service Management · What Is a DNS Service?
• GTM · What Is GTM (Global Traffic Manager)?
• DNS Forwarder Profiles

Related questions

• What is the difference between Load Balancer and GTM; which one should I use?
• How do I health check DNS servers?
• Can I load balance UDP traffic (DNS, Syslog, NTP)?
• What does the configuration error(s) warning in the vService preview (DNS Resolution Error, Port binding error) mean; where does Port Collision appear?