Secondary DNS Glossary
Table of Contents
A reference for secondary DNS terminology. For the entry point to this category, see Secondary DNS at DNSimple. For broader DNS terms, see the DNS Glossary, and for delegation terms see the Name Servers Glossary.
Roles and directions
Primary
The DNS provider that holds the zone you edit. The primary is the source of truth: records are created and changed there, and other providers copy from it.
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Secondary
A DNS provider that copies zone data from the primary and answers queries for the zone using its own name servers. A secondary does not accept record edits.
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- Secondary DNS in the Name Servers Glossary
Leader
The wording DNSimple uses for the primary role. The Add new menu on the Domain Names page offers “Secondary DNS zone (with DNSimple as leader)”, meaning DNSimple holds the zone and another provider copies it.
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Follower
The wording DNSimple uses for the secondary role. The Add new menu on the Domain Names page offers “Secondary DNS zone (with DNSimple as follower)”, meaning another provider holds the zone and DNSimple copies it.
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Outbound secondary DNS
DNSimple as primary. You edit the zone at DNSimple and your other provider transfers it out. Configured from the Secondary DNS card on the domain DNS page.
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Inbound secondary DNS
DNSimple as secondary. Another provider holds the zone and DNSimple transfers it in. Created from Domain Names > Add new > Secondary DNS zone (with DNSimple as follower). Primary servers are added and linked from inside the secondary zone.
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Hidden primary
A topology where the authoritative primary is not listed in the public delegation. Resolvers only ever see the secondary name servers, while the primary sits out of sight and serves transfers to them. This is a way of arranging inbound secondary DNS rather than a separate DNSimple product.
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Zone transfers
Zone transfer
The mechanism that copies zone data from a primary to a secondary. Zone transfers move records only. They do not move private DNSSEC signing keys, which is why DNSSEC and secondary DNS need planning.
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AXFR
A full zone transfer. The secondary requests the zone and the primary sends every record. AXFR is the standard mechanism for secondary DNS and the one DNSimple uses in both directions.
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IXFR
An incremental zone transfer. Where AXFR sends the whole zone, IXFR sends only what changed since a given serial, when both the primary and the secondary support it.
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NOTIFY
A message from a primary telling its secondaries that the zone changed, so they can request a transfer instead of waiting for their refresh timer. Without NOTIFY a secondary still updates, but only when its own timer expires.
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SOA serial
A version number in the zone’s SOA record. It increases whenever the zone changes, and it is how a secondary knows whether the copy it holds is current. Comparing serials across providers is the quickest way to tell whether a transfer happened.
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Refresh interval
A value in the SOA record telling a secondary how often to check the primary for a new serial. It is the fallback that keeps a zone updating when no NOTIFY arrives. DNSimple treats a secondary as in sync only when the serial, the refresh value, and the SOA primary name server field all match the zone as published at axfr.dnsimple.com.
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What you configure at DNSimple
Secondary DNS configuration
The outbound setup on a domain: which name servers your secondary provider will answer from, and which addresses may transfer the zone. One configuration per domain.
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Secondary zone
The inbound object representing a zone DNSimple copies from somewhere else. A new secondary zone has no records until it is linked to at least one primary server and a transfer completes.
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Primary server
The inbound object describing where DNSimple transfers from: a name, a public address, and a port. A primary server is defined once for the account and can be linked to more than one secondary zone.
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Whitelisted IPs
The addresses allowed to transfer your zone out of DNSimple. They serve a second purpose as well: DNSimple sends NOTIFY to them, so a provider missing from this list may never be told the zone changed. NOTIFY goes to individual addresses only. A CIDR range permits transfers from the whole range but does not receive notifications.
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Transfer endpoint
The host your secondary provider transfers from, axfr.dnsimple.com. Some providers ask for the host name and others for its addresses.
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Have more questions?
If you have any questions about secondary DNS, contact support, and we will be happy to help.