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To run Dynamic DNS on infrastructure you control, operate an authoritative BIND 9 primary for your domain, allow only authenticated RFC 2136 updates, and run nsupdate whenever your public IPv4 or IPv6 address changes. Delegate the zone to that server (and, where reliability matters, a read-only secondary), keep DNS reachable on UDP and TCP port 53, and send every update to the primary named by the zone’s SOA record. The result is a self-hosted authoritative service rather than a forwarding or caching resolver.
What you are building
Dynamic DNS (DDNS) changes an authoritative A record for IPv4, an AAAA record for IPv6, or both when an endpoint’s address changes. In a self-hosted design, BIND 9 is the authoritative software. One server is the writable primary (also called the master); optional secondary servers copy the zone through normal transfers and answer queries from read-only data.
The update path has four parts:
- A domain whose DNS delegation points at reachable authoritative nameservers.
- A BIND primary that loads the zone and accepts RFC 2136 UPDATE messages.
- A TSIG key, or an equivalent authenticated policy, shared by BIND and the updater.
- An updater on the changing-IP host or router that replaces the old address with the current one.
DNS UPDATE is standardized by RFC 2136. Updates are transactional: all prerequisites must succeed or no change is applied. Without authentication, anyone able to reach the authoritative server could alter records, so an unauthenticated public update endpoint is not an acceptable configuration.
Decide whether self-hosting fits
Self-hosting gives you direct control over BIND’s update policy, keys, logging, DNSSEC behavior, and server placement. It also makes you responsible for Internet reachability, patching, monitoring, backups, and redundancy. A managed authoritative DNS service removes the need to expose and maintain your own primary, but its policy, API, and operational controls are outside your server.
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| Consideration | Self-hosted BIND primary | Managed authoritative DNS |
|---|---|---|
| Update policy | You define RFC 2136 permissions and key scope. | The provider defines its API or update mechanism. |
| Reachability | Your host, firewall, NAT, ISP and delegation must remain reachable. | The provider operates the authoritative fleet. |
| Redundancy | You arrange a secondary or additional primary infrastructure. | Redundancy is part of the service design. |
| DNSSEC | You configure signing and key operations in BIND. | The provider supplies its own signing workflow. |
| Operations | You patch, monitor, log and recover the service. | Less server administration, but dependence on provider tooling. |
| Cost | Domain, server, connectivity and administration costs vary by your design. | Service fees vary by provider and usage. |
Do not put the only authoritative server on a connection whose address changes. If the nameserver’s own address changes, the parent delegation (and possibly glue records) must also change, creating an outage window. Put the primary on a stable host or use a managed secondary that remains reachable while your dynamic endpoint changes.
Prerequisites and delegation
Register a domain and choose the zone
You need authority over a registered domain, such as example.com, and a name you intend to update, such as home.example.com. The zone can be the entire domain or a delegated child zone. Decide whether the updater will maintain only one hostname or several; that decision determines the narrowest useful update policy.
Provide authoritative servers
Arrange at least one Internet-reachable authoritative server. Operationally, a second authoritative server is preferable: the secondary should be read-only and obtain data from the primary by zone transfer. Publish both nameservers at the parent when your resilience requirements justify it. If your registrar requires glue records for in-bailiwick nameservers, create those glue records with the registrar as well as the NS delegation.
Make transport possible
Authoritative DNS uses both UDP and TCP port 53. Permit inbound traffic on both protocols at the host firewall, edge firewall and NAT device. Some ISPs block inbound port 53 or prohibit servers on residential plans; check that policy before building the service. Confirm that the delegated nameserver address is not itself dependent on the changing record.
Plan IPv4 and IPv6 separately
An A update does not create an AAAA record, and an AAAA update does not replace an A record. If the endpoint has both address families, update each deliberately. IPv6 firewall rules, WAN interface detection and delegation must be tested independently; a working IPv4 path does not prove that IPv6 queries or updates can reach the server.
Install BIND 9 and declare a primary zone
Install the BIND 9 server and client utilities using your operating system’s supported packages. On Debian-based systems, the packages are commonly named bind9, bind9utils and dnsutils; other distributions use different package names and configuration paths. Keep the example paths below consistent within your system and validate the configuration before restarting the daemon.
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Create the zone definition
Declare the zone as a primary (some releases accept the historical word master as an alias). A minimal structure looks like this:
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zone "example.com" {
type primary;
file "/var/lib/bind/db.example.com";
update-policy {
grant ddns-key name home.example.com A AAAA;
};
};The exact file location is distribution-dependent. The important properties are that BIND owns the writable zone file and that the update policy grants only the intended key, owner name and record types. If you prefer an address-based rule, use allow-update with a TSIG key, but do not combine broad address trust with a publicly reachable server. An explicit update-policy is usually easier to scope when several names or record types have different permissions.
Keep a valid initial zone
Place a syntactically valid SOA and NS set in the zone file before starting BIND. The SOA’s MNAME field identifies the primary master. Do not manually edit a zone that is under dynamic control while BIND is running; direct edits can be overwritten or leave journal and serial state inconsistent. Make changes through UPDATE requests, or stop BIND and follow your distribution’s documented journal-handling procedure.
Check and load the configuration
- Run the configuration checker supplied with BIND (for example,
named-checkconf) against the main configuration. - Run the zone checker (for example,
named-checkzone example.com /var/lib/bind/db.example.com) against the zone file. - Reload or restart BIND using your service manager only after both checks pass.
- Inspect the service log for syntax errors, permission failures, refused updates or failed zone loads.
Create and protect the TSIG key
TSIG authenticates the updater to BIND. The secret must exist on the primary and on every client that sends updates. Protect it like a password: readable only by the BIND process and the updater account, excluded from public repositories and backups that are not encrypted, and rotated if exposure is suspected.
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BIND can create a local-ddns session key for local clients. This is convenient when the updater runs on the same host and your distribution enables the local update mechanism. Confirm where the daemon stores that key and which local socket or policy it authorizes before relying on it; do not copy a local key to an untrusted router without understanding its scope.
Use an explicit key for a router or remote client
For a separate router, generate a dedicated TSIG key with BIND tooling such as ddns-confgen or tsig-keygen. Install the resulting key stanza in BIND’s configuration and copy only the secret and algorithm details required by the router. A typical key declaration is:
key "ddns-key" {
algorithm hmac-sha256;
secret "BASE64_SECRET_FROM_KEY_GENERATOR";
};Use the key name exactly as generated when writing the grant rule and when invoking nsupdate. If your BIND build or router supports a different TSIG algorithm, select one supported by both ends; never substitute a plaintext password in an UPDATE command.
Scope permissions narrowly
Grant only the names and types that the client must change. For a single dual-stack hostname, permitting home.example.com with A and AAAA is materially safer than granting the entire example.com zone or every record type. Use separate keys for separate devices when you need independent revocation and auditing.
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Delegate the zone and test authoritative reachability
At the registrar or parent DNS operator, publish NS records pointing to your authoritative nameserver names and supply glue where required. Wait for the parent delegation to appear, then query from a network outside your home connection. Test both UDP and TCP because large responses, DNSSEC data and fallback behavior can require TCP.
dig @198.51.100.53 example.com SOA
dig +tcp @198.51.100.53 example.com SOAReplace the address with your server’s real stable address. The response should contain the expected zone and an SOA whose MNAME is your primary. If the server is behind NAT, forward both protocols and verify that the public address in the delegation reaches the correct internal host.
Send a Dynamic DNS update with nsupdate
The Debian nsupdate manual defines the utility as a client for submitting Dynamic DNS Update requests specified by RFC 2136. It supports TSIG credentials with -k (key file) and -y (algorithm and secret supplied on the command line). Prefer -k so the secret does not appear in process listings or shell history.
Identify the correct destination
Discover the primary by querying the zone’s SOA:
dig +short SOA example.comThe first field is the zone name, the second is the SOA MNAME. Send the UPDATE to that primary, not automatically to a secondary. A secondary that receives an update does not edit its own copy directly; it obtains the changed data from the primary through normal transfer mechanisms.
Replace an IPv4 address
Create a request that deletes the old A value and adds the current one. Deleting the owner name’s A set first avoids leaving a stale address when your ISP assigns a new one:
nsupdate -k /etc/bind/ddns.key <<'EOF'
server ns1.example.com
zone example.com
update delete home.example.com A
update add home.example.com 60 A CURRENT_IPV4
send
EOFCURRENT_IPV4 represents the address detected by your updater; replace it with the actual value or generate the request from a script. The 60-second TTL in this example is a policy choice, not a protocol requirement. A shorter TTL can reduce stale-cache time after a change but increases query traffic.
Replace an IPv6 address
Use the same transaction pattern with AAAA:
nsupdate -k /etc/bind/ddns.key <<'EOF'
server ns1.example.com
zone example.com
update delete home.example.com AAAA
update add home.example.com 60 AAAA CURRENT_IPV6
send
EOFWhen both families change, include both record sets in one request if your policy permits them. RFC 2136 atomicity means a failed prerequisite prevents the transaction from being partially applied.
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Run updates only when the address changes
The updater should read the current WAN address, compare it with the last successfully published value, and call nsupdate only on a difference. Record the last success and the server’s response in a protected state file or service log. If the client cannot contact the primary, retain the previous value and retry with back-off rather than deleting the record and leaving the hostname empty.
Configure a router updater
A router is often the best place to detect a changing public address because it sees the WAN lease directly. OpenWrt’s documented flow installs the ddns-scripts-nsupdate package, runs ddns-confgen on the BIND server, and configures the router to send updates for the current interface. For dual-stack service, enable the IPv6 path against the WAN6 interface rather than assuming the IPv4 interface supplies both values.
- Generate a dedicated TSIG key on the BIND host and add its narrowly scoped policy.
- Install the router’s nsupdate DDNS package using the distribution’s package manager.
- Enter the zone, hostname, primary server, key name, algorithm and secret in the router’s DDNS configuration.
- Select the interface that actually receives the public address; use the IPv6 interface separately when required.
- Trigger a manual update, then inspect the router log for an accepted UPDATE response.
- Change or renew the WAN address in a controlled test and confirm that the router retries and publishes the new value.
Do not paste a key into a web interface that stores configuration world-readable. Check file permissions and the router’s backup behavior, and revoke that key if the device is replaced.
Verify the change from outside your network
Testing from the same LAN can hide NAT, split-DNS and firewall mistakes. Use a mobile connection, a remote host or another independent network.
- Query the authoritative primary directly:
dig @ns1.example.com home.example.com A +noall +answer. - Repeat for
AAAAwhen IPv6 is enabled. - Query through the delegated nameservers without specifying a server to test the parent delegation path.
- Inspect the SOA serial and confirm it advanced after the update. BIND manages the serial and journal for dynamic zones; do not hand-edit it during normal operation.
- Check the secondary, if present, after transfer completes and confirm it returns the same address.
Allow for resolver caching according to the TTL you selected. A successful authoritative response proves the zone changed; a recursive resolver may continue returning the previous value until its cached TTL expires.
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DNSSEC can coexist with RFC 2136 updates, but the zone must be configured so signatures are regenerated when A, AAAA or other signed data changes. In BIND this generally means using the secure-zone and inline-signing behavior appropriate to your version and key-management design. Test the signed response after an update, including the DNSKEY and RRSIG chain, and monitor signing logs. Updating unsigned data in a zone whose signatures are not refreshed can produce validation failures even though the address itself is correct.
Security and operational safeguards
- Authenticate every update. Use TSIG or an equivalent mechanism; never expose an open UPDATE service.
- Limit authority. Restrict each key to the required owner names and A/AAAA types.
- Protect secrets. Set restrictive permissions, avoid command-line secrets where possible, and rotate keys after suspected disclosure.
- Keep the primary writable only where needed. Secondaries should serve transferred data and should not be treated as alternate write targets.
- Patch and monitor BIND. Watch service logs, refused updates, failed transfers, journal growth and unexpected record changes.
- Back up deliberately. Preserve configuration, key material and a tested recovery procedure. Dynamic zone journals are part of the live state; follow BIND’s documented procedure before copying or restoring them.
- Rate-limit and filter. Firewall DNS management paths, permit transfers only to configured secondaries, and avoid exposing administrative interfaces on the public address.
- Plan key revocation. A separate key per router or host lets you disable one client without interrupting every DDNS device.
Troubleshooting by symptom
“REFUSED” from nsupdate
Check that the request reached the SOA MNAME, that the key name and secret match exactly, and that the zone’s update-policy grants the requested owner name and record type. A secondary or a server with no matching policy commonly returns REFUSED.
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“NOTAUTH” or an unexpected SOA
The server may not be authoritative for the zone you specified, or delegation may still point elsewhere. Query the server directly for SOA and verify the zone name, NS records and parent delegation.
The update succeeds but public lookups show the old address
Compare an authoritative query with a recursive query. If the primary returns the new value, wait for cached TTL expiry and check intermediate resolvers. If the primary is stale, inspect the updater’s detected address, key permissions and BIND logs.
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Confirm that the primary’s SOA serial advanced, that the secondary is listed in the zone’s NS set, and that TCP transfers are allowed between the servers. A secondary does not learn changes from the updater directly; it transfers them from the primary.
Queries fail after an address change
Verify that the nameserver’s own delegated address did not change, that port 53 forwarding still targets the server, and that both UDP and TCP are permitted. If the authoritative host itself is dynamic, move the service to a stable address or add a managed secondary before relying on it for delegation.
IPv6 works intermittently
Check that the router is reading the WAN6 address rather than a temporary or link-local address, that AAAA updates are authorized, and that IPv6 firewall rules allow DNS traffic. Test from an IPv6-capable external network.
Costs, maintenance and a practical decision rule
The protocol itself does not impose a published per-update statistic or a fixed cost. Your total cost consists of domain registration, a reachable host or VPS, bandwidth, backup and monitoring resources, and the time required to maintain BIND. A managed service trades some control for provider-operated reachability and redundancy. Choose self-hosting when you need direct control of software, policy or keys and can operate an Internet-facing authoritative service; choose managed DNS when eliminating that operational burden is more valuable than running the primary yourself.
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Reference behavior to keep in mind
RFC 2136 defines authenticated add, replace and delete operations and their atomic prerequisite processing. The Debian nsupdate(1) manual documents the command-line client and its TSIG options. ISC operational guidance explains that clients discover the update destination from the zone SOA and that the MNAME identifies the primary. Those rules are independent of which router, script or operating system initiates the request.
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