Advanced DNS
The zone and its file, the SOA and the serial number, transfer from primary to secondary, delegation and glue, the reverse zone and the difference between authoritative and recursive servers.
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Authoritative server: what is it?
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A DNS server that holds the records of a zone and answers with the “aa” flag; it looks nothing up elsewhere.
In contrast, a recursive resolver queries other servers on the client's behalf and caches the answers.
A host wants to resolve
www.example.org. Which server does it send its query to?- The recursive resolver named in its network configuration
- The authoritative server for the example.org zone
- A root server, which knows the start of every name
- The .org server, which manages all its subdomains
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The recursive resolver named in its network configuration
The host does not walk the tree itself: it sends a recursive query to the configured resolver, often received through DHCP (option 6). That resolver queries the root, then .org, then the authoritative server, and caches the answer.
In the SOA, the … delay says how often the secondary compares serial numbers, and … says after how long without news it stops answering.
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In the SOA, the refresh delay says how often the secondary compares serial numbers, and expire says after how long without news it stops answering.
retry, for its part, sets the delay before a new attempt when the primary does not answer.DNS zone: what is it?
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The part of the name tree whose records one primary server manages, described in a zone file.
A zone stops where a delegation begins:
example.organdlabo.example.orgcan be two zones, managed by two teams.