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Install Ubuntu’s BIND9 package, define your zones in /etc/bind/named.conf.local, create correctly serialised forward and reverse zone files, validate them with named-checkconf and named-checkzone, then query the server with dig. A local BIND configuration makes the server authoritative on the network, but public Internet answers also require correct delegation at the parent zone or registrar.
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What an authoritative BIND server does
An authoritative DNS server is the source of truth for one or more zones. A primary (also called master) BIND server reads each zone from a local file and answers with the records published in that file. It is different from a recursive resolver: a resolver looks up answers on behalf of clients, while an authoritative server serves data for zones it controls.
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This guide uses BIND9 on Ubuntu and a documentation domain, example.com, with documentation-only addresses from the TEST-NET ranges. Replace every example name and address before deploying. The same configuration pattern applies to a public domain, an internal zone, or a game-server network, but the delegation and access requirements differ.
Prerequisites and deployment decisions
- An Ubuntu system with administrative access and a stable address. The examples use
192.0.2.10for the nameserver and192.0.2.20for a host; these addresses are reserved for documentation and must not be used on the Internet. - A domain or reverse-address zone that you are authorised to administer. For a public domain, the registrar or parent zone must delegate the domain to the nameserver addresses you operate.
- At least one planned nameserver name, such as
ns.example.com., and the address records needed by clients. - A decision about recursion. An Internet-facing authoritative-only server should not be an open recursive resolver. Review
/etc/bind/named.conf.optionsand set recursion and client access controls for the deployment. - A backup or secondary-server plan. One primary can answer queries, but it is a single point of failure if the host or its network disappears.
For a private network, clients may be configured to query the server directly and no public delegation is needed. For a public service, local configuration alone cannot make the domain reachable; the parent zone must publish the delegation, and a nameserver inside the delegated domain may also require glue at the registrar.
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Install BIND9 and understand Ubuntu’s configuration layout
- Install the package:
sudo apt install bind9Ubuntu’s packaged configuration is under /etc/bind. The main operational configuration is named.conf, which includes other files supplied by the package. Put locally defined authoritative zones in /etc/bind/named.conf.local; keeping local declarations there avoids mixing them with package-managed defaults.
BIND statements have scopes. Global settings belong in an options statement, while a zone statement applies only to one zone. A zone-specific setting is narrower than a global setting and overrides the broader setting where the two conflict. This lets you keep common behaviour in named.conf.options and apply exceptions to one zone without changing every zone.
Before adding zones, review the options file. In particular, decide whether recursion is enabled, which clients may query the server, and which interfaces should listen. An authoritative-only Internet service normally limits recursion and avoids accepting recursive queries from untrusted networks.
Declare a forward zone
A forward zone maps names such as www.example.com to addresses. Add a zone declaration to /etc/bind/named.conf.local:
zone "example.com" {
type master;
file "/etc/bind/db.example.com";
};type master identifies this server as the primary source for the zone. The file path is where BIND reads the zone data. The filename is a local convention; the important part is that it matches the path in the declaration and is readable by the BIND service.
Build the forward zone file
Create /etc/bind/db.example.com with a time-to-live, an SOA record, an NS record, and the address records clients need:
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$TTL 604800
@ IN SOA ns.example.com. root.example.com. (
1 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ; Negative Cache TTL
)
@ IN NS ns.example.com.
ns IN A 192.0.2.10
www IN A 192.0.2.20How to read the records
$TTL 604800sets the default cache lifetime in seconds for records that do not specify another TTL.- The
SOArecord names the primary server (ns.example.com.) and the responsible mailbox in DNS form (root.example.com., where the first dot represents the usual mailbox separator). Serialis the zone version. Increment it on every edit. Secondaries use the changed serial to decide whether to transfer new data.Refresh,Retry, andExpirecontrol secondary-server polling and how long a secondary may continue serving data when it cannot contact the primary.Negative Cache TTLcontrols how long resolvers may cache a negative response such as a name that does not exist.- The apex
NSrecord delegatesexample.comtons.example.com.. The trailing dot is significant: it makes the name fully qualified instead of causing BIND to append the zone name again. - The
Arecords map the nameserver and web host to IPv4 addresses. Add the record types your services actually use, such as additionalAorAAAArecords.
Use a fully qualified name with a trailing dot in SOA and NS values. A missing dot can produce an unintended name such as ns.example.com.example.com.. Keep the serial consistent with your change process; a serial that does not increase leaves secondaries serving old data even when the file has changed.
Add a reverse DNS zone
Reverse DNS maps an address back to a hostname through a PTR record. IPv4 reverse zones use the in-addr.arpa namespace and reverse the address octets in the zone name. For addresses in 192.168.1.0/24, declare:
zone "1.168.192.in-addr.arpa" {
type master;
file "/etc/bind/db.192";
};Create the referenced file, for example /etc/bind/db.192, and add an SOA plus PTR records whose owner names are the remaining, unreversed octets:
$TTL 604800
@ IN SOA ns.example.com. root.example.com. (
1 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ; Negative Cache TTL
)
@ IN NS ns.example.com.
10 IN PTR ns.example.com.
20 IN PTR www.example.com.In this example, the owner 20 under 1.168.192.in-addr.arpa represents 192.168.1.20. Reverse delegation is controlled by the organisation that owns the address block. For a private address range, configure the internal DNS clients and network infrastructure; for a public block, the upstream provider must delegate the reverse zone to your nameserver.
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Check the global configuration and each zone before activating changes. Validation catches syntax errors without interrupting a running service:
sudo named-checkconf
sudo named-checkzone example.com /etc/bind/db.example.com
sudo named-checkzone 1.168.192.in-addr.arpa /etc/bind/db.192named-checkconf reports errors in the BIND configuration files. named-checkzone parses one zone file against the zone name you provide. A successful check includes the loaded serial and OK. Treat warnings seriously when they concern missing names, malformed owner names, or unexpected record data; a syntactically valid file can still publish the wrong answer.
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Run the checks again after changing a zone or its declaration. Checking only the forward zone does not validate a newly added reverse zone, and checking a file with the wrong zone name can hide an error in the intended declaration.
Restart the service and inspect its status
Once every check succeeds, restart the packaged service and inspect the result:
sudo systemctl restart bind9.service
sudo systemctl status bind9.serviceA failed restart usually points to a configuration or file-permission problem. Read the status output and the service journal, correct the reported file or statement, run the validation commands again, and restart only after they pass. Keeping validation before every restart prevents a typo from turning a planned DNS edit into an outage.
Test authoritative answers with dig
Query the server directly rather than relying on a recursive resolver that may have cached an older answer:
dig @192.0.2.10 example.com SOA
dig @192.0.2.10 www.example.com A +norecurse
dig @192.0.2.10 -x 192.0.2.20- The SOA query confirms that the server has loaded the zone and exposes the current serial.
- The direct
Aquery asks for the host record without requesting recursion. In the response flags,aameans the answer is authoritative for the name. - The
-xquery performs the reverse lookup and should return the corresponding PTR value when the reverse zone is configured and delegated to this server.
Check both the answer section and the authority flags. An answer returned without aa may have come from recursion or cache and does not prove that this BIND instance is authoritative. Query the server’s actual listening address, not a different resolver on the same network.
Make public delegation match your server
For a public domain, configure the parent zone or registrar to delegate the domain to the nameserver names published in your zone. The parent must also know the addresses of those nameservers. If a nameserver name is inside the domain it serves, the registrar may need glue records so resolvers can find its address without a circular lookup.
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After delegation changes, use direct queries to your server to separate local BIND problems from parent-zone problems. If direct queries show an authoritative answer but public resolvers do not, inspect the parent delegation, nameserver addresses, firewall rules, and propagation or caching at the querying resolver. A correct zone file cannot override a missing or incorrect parent delegation.
Add a secondary server for availability
A single primary is simple but fails whenever its host, storage, network path, or service fails. Ubuntu recommends a secondary server that obtains the zone from the primary. On the primary, restrict transfers to the secondary’s address in each zone declaration:
zone "example.com" {
type master;
file "/etc/bind/db.example.com";
allow-transfer { SECONDARY_IP; };
};Replace SECONDARY_IP with the secondary’s real address, apply the same transfer restriction to every authoritative zone, and restart BIND after validation. Configure the secondary as a slave that loads the zone from the primary. Do not permit unrestricted transfers: a zone transfer can disclose the complete set of names and addresses in a zone.
| Design | Availability during primary failure | Transfer and access control | Operational complexity | DNSSEC and key-management impact |
|---|---|---|---|---|
| One primary | No alternate source; queries fail if the only server is unreachable. | No inter-server transfer policy is required, but query access still needs appropriate controls. | Lowest; one host and one set of zone files. | Keys and signing are managed on one system. |
| Primary plus secondary | Secondary can continue answering while the primary is unavailable, subject to its cached zone lifetime. | Transfers should be limited with allow-transfer to the secondary address. |
Higher; monitor transfers, serials, connectivity, and both services. | Plan where signing occurs and how keys and signed data reach the secondary. |
Adding reverse zones improves address-to-name diagnostics, while adding a secondary improves resilience. A forward-only primary is the smallest configuration; each additional zone and server increases the number of files and checks you must maintain.
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DNSSEC is a follow-on hardening step, not a substitute for correct zone data and delegation. Ubuntu defines it as “a set of security extensions to DNS which allow DNS data to be verified for authenticity and integrity.” Signing adds records such as DNSKEY, RRSIG, and a parent-published DS record.
Start with an existing authoritative zone that already validates and answers correctly. Ubuntu’s DNSSEC procedure uses a writable directory such as /var/lib/bind for signed-zone operation. This matters because the signing process must create or update generated records without modifying a read-only package area. Plan file ownership, permissions, key backups, rollover procedures, and how the parent receives the DS record before enabling validation for users.
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DNSSEC key management adds operational work to both single-server and primary-plus-secondary designs. Decide which system signs, where private keys are stored, how signed files are transferred, and how you will recover from a lost or expired key. Do not publish a DS record at the parent until the corresponding DNSKEY and signatures are being served consistently.
Troubleshoot the common failure modes
“The service will not restart”
Run sudo named-checkconf first, then check every zone with named-checkzone. Look for missing braces or semicolons in named.conf.local, an incorrect zone-file path, and a zone file whose owner name or SOA syntax is malformed. Correct the first reported error, validate again, and only then restart.
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“The query returns no answer”
Confirm that the queried name is actually present in the zone file, that its record uses the intended owner name, and that the SOA serial reflects the latest edit. Query the server directly with dig @SERVER_IP name TYPE +norecurse so a recursive cache cannot obscure the result.
“The answer is not authoritative”
Ensure the query is sent to the BIND address that loaded the zone and inspect the response for the aa flag. If the flag is absent, you may be querying a resolver, a different local service, or a server that has not loaded the zone declaration. Check service status and the SOA response from the target address.
“A secondary has stale data”
Increase the SOA serial after every edit, verify that allow-transfer includes the secondary’s address, and confirm that network controls permit DNS zone transfers between the two servers. The secondary compares serials; leaving the serial unchanged tells it that no new version exists.
“Direct tests work but public lookups fail”
Inspect parent delegation and nameserver address records. Verify that each delegated nameserver is reachable on the required DNS transport, that glue exists when a nameserver is inside the delegated domain, and that the parent has the current addresses. This is a delegation problem rather than a zone-file parsing problem when direct authoritative queries succeed.
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Recheck the reversed octets in the in-addr.arpa zone name and the PTR owner. For a /24 network, only the final address octet appears as the owner beneath the three reversed network octets. Confirm that the reverse zone is delegated by the address-space owner when the addresses are public.
Quick Recap
Operational checklist
- Keep local zone declarations in
/etc/bind/named.conf.localand zone data in the paths referenced by those declarations. - Use fully qualified names with trailing dots in SOA and NS records.
- Increment every zone’s SOA serial whenever its data changes.
- Run
named-checkconfandnamed-checkzonefor all affected zones before restarting. - Inspect
systemctl status bind9.serviceafter activation. - Test SOA, forward, and reverse answers directly with
dig, and confirm the authoritativeaaflag. - Keep recursion and client access controls appropriate to the network; never expose an unintended open recursive resolver.
- Restrict zone transfers to known secondary addresses with
allow-transfer. - Maintain parent and reverse delegations separately from local BIND files.
- Treat DNSSEC as a planned key-management project using writable signed-zone storage such as
/var/lib/bind, rather than enabling it before unsigned authority is reliable.
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