Frequently asked questions about Knot DNS with detailed answers for Linux DevOps professionals covering installation, configuration, security, and troubleshooting.
Knot DNS is a high-performance, authoritative-only DNS server developed by CZ.NIC, the registry for the .cz top-level domain. Unlike recursive resolvers like Unbound or BIND in recursive mode, Knot DNS is designed exclusively for authoritative DNS serving. This means it only responds to queries for zones it manages, not general internet lookups.
Key differences from other DNS servers:
Knot DNS is ideal for:
It may not be suitable if you need a recursive resolver or simple caching DNS server.
Minimum requirements:
For production environments with thousands of zones or high query rates, consider:
Debian/Ubuntu:
sudo apt update
sudo apt install knot knot-dnsutils
RHEL/CentOS/Fedora/Rocky:
sudo dnf install knot knot-utils
From source (latest features):
wget https://secure.nic.cz/files/knot-dns/knot-3.5.3.tar.xz
tar -xf knot-3.5.3.tar.xz
cd knot-3.5.3
./configure --prefix=/usr/local --with-systemd
make
sudo make install
After installation, verify everything is working:
# Check version
knotd -V
# Check configuration syntax
sudo knotc conf-check
# Start and check service status
sudo systemctl start knot
sudo systemctl status knot
# Test local resolution
kdig @127.0.0.1 localhost
/etc/knot/knot.conf/var/lib/knot//var/log/knot/ (if configured)/run/knot.pid/usr/sbin/knotdCreate a basic configuration in /etc/knot/knot.conf:
server:
listen: [ 0.0.0.0@53, ::@53 ]
workers: 2
database:
storage: /var/lib/knot
zone:
- domain: example.com
file: /var/lib/knot/zones/example.com.zone
Create the zone file /var/lib/knot/zones/example.com.zone:
$ORIGIN example.com.
$TTL 3600
@ IN SOA ns1.example.com. admin.example.com. (
2026021401 ; serial
7200 ; refresh (2 hours)
3600 ; retry (1 hour)
1209600 ; expire (2 weeks)
3600 ) ; minimum (1 hour)
IN NS ns1.example.com.
IN A 192.168.1.10
ns1 IN A 192.168.1.10
www IN A 192.168.1.11
Then reload the configuration:
sudo knotc reload
Enable DNSSEC in your zone configuration:
zone:
- domain: example.com
file: /var/lib/knot/zones/example.com.zone
dnssec-signing: on
dnssec-policy: default
policy:
- id: default
algorithm: ECDSAP256SHA256
propagation-delay: 2d
rrsig-lifetime: 30d
automatic-ksk-rollover: on
Generate keys and check DS records:
# Generate keys
sudo keymgr example.com key-create ksk algorithm=ecdsap256
sudo keymgr example.com key-create zsk algorithm=ecdsap256
# Get DS records for delegation
sudo keymgr example.com ds-publish
Use TSIG keys for secure zone transfers:
# Define TSIG key
key:
- id: transfer_key
algorithm: hmac-sha256
secret: "your-very-secure-secret-here"
# Define ACL for transfers
acl:
- id: secure_transfer
address: [ 192.168.1.100 ] # Secondary server IP
key: transfer_key
action: [ transfer ]
# Apply ACL to zone
zone:
- domain: example.com
file: /var/lib/knot/zones/example.com.zone
acl: [ secure_transfer ]
Key performance settings:
server:
listen: [ 0.0.0.0@53, ::@53 ]
# Set workers to number of CPU cores
workers: 4
tcp-workers: 2
# Optimize for your network
max-udp-payload: 1232
# Enable background refresh
background-refresh: on
database:
storage: /var/lib/knot
# Limit journal size to prevent disk exhaustion
journal-max-usage: 500MiB
Use the statistics module:
module:
- id: global_stats
load: stats
zone:
- domain: example.com
module: [ global_stats ]
Check statistics:
# View server statistics
sudo knotc stats server
# View zone statistics
sudo knotc stats zone example.com
Essential security configurations:
acl:
- id: secure_transfer
address: [ 192.168.1.0/24 ]
key: transfer_key
action: [ transfer ]
server:
listen: [ 0.0.0.0@53, ::@53 ]
rrl-whitelist-ratio: 0.1
rrl-slots: 10000
rrl-max-ratelimit: 200
sudo chown -R knot:knot /etc/knot/
sudo chmod 750 /etc/knot/
sudo chmod 640 /etc/knot/knot.conf
Knot DNS primarily serves authoritative zones and doesn’t typically handle encrypted client queries. For encrypted upstream queries, consider using a recursive resolver like Knot Resolver in front of your authoritative servers.
For authoritative server security, focus on:
sudo knotc conf-check
sudo knotc conf-show
sudo kzonecheck /var/lib/knot/zones/example.com.zone
sudo knotc zone-check example.com
sudo journalctl -u knot -f
sudo knotc conf-show acl
sudo keymgr list
dig @primary-server example.com AXFR
telnet secondary-server 53
Common causes and solutions:
sudo chown knot:knot /var/lib/knot/zones/example.com.zone
sudo chmod 644 /var/lib/knot/zones/example.com.zone
sudo kzonecheck /var/lib/knot/zones/example.com.zone
sudo knotc conf-check
sudo mkdir -p /var/lib/knot/zones
sudo chown knot:knot /var/lib/knot/zones
For zero-downtime updates:
# Validate new configuration
sudo knotc conf-check
# Reload without restart
sudo knotc reload
# Reload specific zone
sudo knotc zone-reload example.com
Backup procedure:
#!/bin/bash
BACKUP_DIR="/backup/knot/$(date +%Y%m%d_%H%M%S)"
mkdir -p "$BACKUP_DIR"
# Backup configuration
sudo cp /etc/knot/knot.conf "$BACKUP_DIR/"
# Backup zones
sudo tar -czf "$BACKUP_DIR/zones.tar.gz" -C /var/lib/knot zones/
# Backup DNSSEC keys (encrypt them)
sudo tar -czf "$BACKUP_DIR/keys.tar.gz" -C /var/lib/knot keys/
gpg --encrypt --recipient admin@example.com "$BACKUP_DIR/keys.tar.gz"
echo "Backup completed to $BACKUP_DIR"
Restore procedure:
# Stop service
sudo systemctl stop knot
# Restore configuration
sudo cp backup-location/knot.conf /etc/knot/
# Restore zones
sudo rm -rf /var/lib/knot/zones/*
sudo tar -xzf backup-location/zones.tar.gz -C /var/lib/knot/
# Restore keys (if needed)
gpg --decrypt backup-location/keys.tar.gz.gpg | sudo tar -xzf - -C /var/lib/knot/
# Set permissions
sudo chown -R knot:knot /var/lib/knot/
sudo chown knot:knot /etc/knot/knot.conf
# Start service
sudo systemctl start knot
| Feature | Knot DNS | PowerDNS |
|---|---|---|
| Architecture | Authoritative-only | Both authoritative and recursive |
| Performance | High (lock-free) | High |
| DNSSEC | Built-in, strong tooling | Good support |
| Database Backends | Custom | MySQL, PostgreSQL, SQLite, etc. |
| Zone Transfer | Native IXFR/AXFR | Native IXFR/AXFR |
| Dynamic Updates | Full support | Full support |
| API | Configuration file | REST API |
| Feature | Knot DNS | BIND |
|---|---|---|
| Performance | Higher for authoritative | Lower for authoritative |
| Configuration | Centralized YAML-like | Separate files |
| DNSSEC | Modern tooling | Traditional tooling |
| Memory Safety | C with modern practices | C with long history |
| Zone Transfer | Efficient IXFR | Standard AXFR/IXFR |
| Security Track Record | Good | Extensive but older |
| Feature | Knot DNS | NSD |
|---|---|---|
| Architecture | Multi-threaded | Multi-threaded (NSD 4.x+) |
| Zone Updates | Dynamic updates (DDNS) | Static zones (zone file reload required) |
| DNSSEC | Automatic signing with key management | Manual signing (external tools) |
| IXFR | Native support | Limited support |
| Configuration | YAML configuration file | Simple configuration file |
| Dynamic Records | Supported | Not supported |
| Catalog Zones | Supported | Not supported |
Note: NSD (Name Server Daemon) is developed by NLnet Labs and is designed for simplicity and stability. While NSD 4.x introduced multi-threading, it lacks dynamic update capabilities and has more limited DNSSEC automation compared to Knot DNS.
Use configuration management tools like Ansible:
- name: Deploy Knot DNS
hosts: dns_servers
become: true
tasks:
- name: Install Knot DNS
package:
name: knot
state: present
- name: Deploy configuration
template:
src: knot.conf.j2
dest: /etc/knot/knot.conf
owner: knot
group: knot
mode: '0640'
notify: reload knot
- name: Start service
systemd:
name: knot
state: started
enabled: true
Add Knot DNS to your monitoring stack:
# Check if service is running
systemctl is-active --quiet knot
# Check configuration validity
knotc conf-check
# Monitor specific zones
knotc zone-status example.com
# Export metrics to Prometheus (using stats module)
curl http://localhost:9153/metrics
For automated DNSSEC key management:
#!/bin/bash
DOMAIN="example.com"
# Check key status
keymgr "$DOMAIN" key-list
# Check for upcoming expirations
keymgr "$DOMAIN" key-list | grep -E "(expire|next)"
# Rotate keys if needed (scripted)
if [ condition_for_rotation ]; then
keymgr "$DOMAIN" key-rollover ksk
fi