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TR7Enterprise Application Delivery & Security Platform
What are master and slave DNS servers?
Short answer
The master DNS server is the original source where the records of a zone are edited; the slave server copies the records from the master with zone transfer and gives authoritative responses for the same zone, so that responses continue to be given even when one server goes out of service. In current DNS terminology these roles are also referred to as primary and secondary (RFC 9499). The slave renews the zone when the SOA serial of the master increases (with the check it makes at the SOA refresh interval) or when it receives a NOTIFY from the master. TR7 GTM works in both roles: with an Express Profiles profile assigned to the domain's data center group, it pulls the records from the external server in the Master Addresses field; with the domain's Slave Server IPs list, it also gives its own zone to slave servers.
Where It Is Used in TR7
| Where | Field / label | What for |
|---|---|---|
| GTM → Express Profiles (DNS Integration) → Add | Master Addresses (at most 10 addresses, default port 53) | The master servers from which TR7 will pull the records |
| GTM → GTM Services → service name → Domains → Add / Edit | The EXPRESS checkbox and the profile selection in the data center group | Making the group receive its records from the master |
| GTM → GTM Services → service name → Records | Sync via Express button | Manual re-transfer from the master |
| GTM → GTM Services → service name → Domains → Add / Edit | Slave Server IPs | The slave servers to which TR7, as master, gives the zone and sends NOTIFY |
The Two Roles of TR7
| TR7 acting as slave (Express) | TR7 acting as master (Slave Server IPs) | |
|---|---|---|
| Source of the records | External master server | Records in TR7 GTM |
| Transfer direction | Master → TR7 | TR7 → slave servers |
| Refresh | NOTIFY coming from the master or Sync via Express; there is no timer-based refresh | TR7 sends NOTIFY at every change; the slaves also check at the SOA refresh interval |
| Record editing | The records of the Express group are read-only on TR7; the change is made on the master | The records are edited on TR7 |
| Cluster | The primary device makes the transfer | The settings are reflected to the peer device |
- The master server must allow the zone transfer request coming from the Frontend IP address of the TR7 DNS service in the same network (or, if there is none, from its cluster VIP) and must send NOTIFY to TR7 on changes; if NOTIFY is not sent, the refresh is done only with Sync via Express.
Common Misconceptions
- "Master/slave in DNS is the same as Master/Slave in the TR7 cluster." Master/Slave in the cluster refers to the device that holds the VIP (What is the Master/Slave role on a VIP?); the roles in DNS indicate the source of the zone records.
- "Records can be edited on the slave server." The slave receives the records from the master; in TR7 too, the record rows of the Express group are read-only in the form.
- "The Express profile polls the master by itself at regular intervals." TR7 does not make a timer-based refresh on the Express side; the master must send NOTIFY.
How it is done in the documentation
