Unbound Knowledge Patch

Unbound Knowledge Patch

Use this skill when configuring, upgrading, operating, or debugging Unbound. Start with the quick references below, then open the topic file that matches the work. Treat deployed configuration, build flags, and observed behavior as authoritative when they differ from generic assumptions.

Reference index

Upgrade-critical configuration

Configure subnet caching explicitly

Building with subnet support no longer inserts subnetcache into module-config. Add it explicitly when ECS-aware caching is required:

server:
    module-config: "subnetcache validator iterator"

Select TLS protocols at runtime

Use tls-protocols to choose supported TLS versions. Do not use the removed tls-use-system-versions or --enable-system-tls controls. If TLS 1.2 is required, avoid 1.24.0 specifically; 1.24.1 permits it again.

Preserve RESPIP and RPZ behavior with DNS64

Use this module order so policy applies to DNS64-synthesized answers:

server:
    module-config: "respip dns64 validator iterator"

Do not assume that inserting cachedb as "respip dns64 validator cachedb iterator" works.

Review serve-expired defaults

serve-expired-ttl defaults to 86400 and serve-expired-client-timeout defaults to 1800. Account for those defaults when upgrading a configuration that relied on implicit values.

Understand wait-limit zero values

wait-limit: 0 disables all wait limits. wait-limit-cookie: 0 can disable limits for cookie-validated clients. A wait-limit rejection returns SERVFAIL; discard-timeout drops UDP queries but retains stream connections.

High-value features

Serve DNS over QUIC

Build with libngtcp2 and a QUIC-capable OpenSSL, then configure a QUIC port and memory allowance:

server:
    quic-port: 853
    quic-size: 8m

A build without DoQ support ignores QUIC ports and warns when quic-port is configured. See the transport and build references for dependency checks.

Override transport per forward zone

Zone-specific transport can override global upstream settings:

server:
    tcp-upstream: no
    tls-upstream: no

forward-zone:
    name: "."
    forward-tcp-upstream: yes
    forward-tls-upstream: yes

Reload with a short service pause

Use fast reload for changed configuration:

unbound-control fast_reload

It parses in a separate thread and pauses service threads briefly. It also propagates supported dnstap, TLS-file, scrub, and quota changes. Key-file errors no longer terminate the daemon, but always inspect the command result and logs before treating the reload as successful.

Reload renewed certificates

Reloads detect changed certificate files and rebuild contexts for DoT, DoH, DoQ, and outgoing DoT. fast_reload handles tls-service-key, tls-service-pem, and tls-cert-bundle, removing the need for a full restart after ordinary certificate renewal.

Inspect selected cache names

Use targeted lookup instead of a full cache dump:

unbound-control cache_lookup example.com
unbound-control cache_lookup +t .

The +t form accepts TLD and root names, and matching subnet-cache content is included.

Isolate control listener ports

Bind a port on each control-interface value:

remote-control:
    control-interface: 127.0.0.1@8953

Persist and rotate EDNS COOKIE secrets

Persist secrets with cookie-secret-file, then rotate them using add_cookie_secret, activate_cookie_secret, and drop_cookie_secret. Inspect active values with print_cookie_secrets.

server:
    cookie-secret-file: "unbound_cookiesecrets.txt"

Bound iterator signature sets

iter-scrub-rrsig caps retained RRSIG records; its default is 8:

server:
    iter-scrub-rrsig: 8

Block one address family locally

Use block_a or block_aaaa to suppress A or AAAA lookups. The _wdata forms can answer matching local-data, recurse for other data, and deny the selected family:

server:
    local-zone: "v4-only.example." block_aaaa_wdata
    local-data: "v4-only.example. 300 IN A 192.0.2.10"

Remove one exact local-data record

Pass a complete RR to avoid deleting every record at the owner name:

unbound-control local_data_remove \
  'host.example. 300 IN A 192.0.2.10'

Diagnostic checkpoints

Cache behavior

• TTL-0 upstream answers are not stored by cachedb; cached records expire at TTL 0.
• forward-no-cache and stub-no-cache suppress external cachedb lookup and storage, including applicable ECS paths.
• A TTL-0 DNAME can yield a synthesized response reused internally for a one-second grace period while clients still receive TTL 0.
• Limit-triggered SERVFAIL results may be cached briefly, so an immediate retry need not repeat recursion.

Validation and policy

• private-address filtering covers matching SVCB and HTTPS records.
• always_refuse local zones block DS queries too.
• DNS64 validates the AAAA lookup and preserves rpz-passthru and ECS cache scope.
• RPZ loading ignores ZONEMD as a policy type.

Encrypted transports

• DoT and DoH use separate SSL contexts and ALPN values.
• Unbound avoids opening unencrypted channels beside encrypted channels on the same port.
• Upstream TLS connections are reused only when the configured TLS name also matches, not merely the resolved address.
• pad-responses applies to DoQ; after referrals, tls-upstream continues to use tls-port.

Auth-zone resilience

• A failed secondary load clears that zone and leaves the daemon running; update attempts continue.
• Missing zonefile-only primary data no longer terminates the daemon.
• Secondary zonefiles cannot use $INCLUDE, and out-of-zone records are discarded during auth-zone and RPZ loads.
• Use max-transfer-size and max-transfer-time to bound transfers; both are disabled by default.

Working method

1. Identify the running binary version, compile options, module order, and active listener configuration.
2. Open the relevant topic reference and apply every interacting rule, not just the first matching option.
3. Validate syntax with unbound-checkconf; its warnings include ineffective nodefault declarations and circular hostname dependencies in stub or forward zones.
4. For runtime changes, inspect the remote-control result, logs, and relevant counters after reload.
5. Test DNSSEC, ECS, policy, cachedb, and encrypted-transport paths separately when more than one module participates.