# Introduction

## What is Knot DNS

Knot DNS is a high-performance open-source DNS server. It implements only the authoritative domain name service. Knot DNS can reliably serve TLD domains as well as any other zones.

Knot DNS benefits from its multi-threaded and mostly lock-free implementation which allows it to scale well on SMP systems and operate non-stop even when adding or removing zones.

The server itself is accompanied by several utilities for general DNS operations or for maintaining the server.

For more info and downloads see www.knot-dns.cz.

## Knot DNS features

DNS features:

- Primary and secondary server operation

- Internet (IN) and limited Chaos (CH) classes

- DNS extension (EDNS0, EDE, EXPIRE, PADDING, ZONEVERSION)

- UDP, TCP, TLS 1.3, and QUIC protocols

- Zone catalog generation and interpretation

- Minimal responses

- Dynamic zone updates

- DNSSEC with NSEC and NSEC3

- ZONEMD generation and validation

- Transaction signature using TSIG

- Full and incremental zone transfers (AXFR, IXFR)

- Name server identification using NSID or Chaos TXT records

- Resource record types A, NS, CNAME, SOA, PTR, HINFO, MINFO, MX, TXT, RP, AFSDB, RT, KEY, AAAA, LOC, SRV, NAPTR, KX, CERT, DNAME, APL, DS, SSHFP, IPSECKEY, RRSIG, NSEC, DNSKEY, DHCID, NSEC3, NSEC3PARAM, TLSA, SMIMEA, CDS, CDNSKEY, OPENPGPKEY, CSYNC, ZONEMD, SVCB, HTTPS, SPF, NID, L32, L64, LP, DSYNC, EUI48, EUI64, URI, CAA, RESINFO, WALLET, and Unknown

Server features:

- IPv4 and IPv6 support

- Semantic zone checks

- Server control interface

- Zone journal storage

- Persistent zone event timers

- YAML-based or database-based configuration

- Query processing modules with dynamic loading

- On-the-fly zone management and server reconfiguration

- Multithreaded DNSSEC zone signing and zone validation

- Automatic DNSSEC key management

- Zone data backup and restore

- Database zone backend

- Offline KSK operation

- PKCS #11 interface

Remarkable module extensions:

- Response rate limiting

- Forward and reverse records synthesis

- DNS request traffic statistics

- Efficient DNS traffic logging interface

- Dnstap traffic logging

- Online DNSSEC signing

- GeoIP response tailoring supporting ECS and DNSSEC

Remarkable supported networking features:

- TCP Fast Open (client and server)

- Opportunistic, strict, and mutual authentication profiles over TLS 1.3 or QUIC

- High-performance UDP, TCP, and QUIC through AF_XDP processing (on Linux 4.18+)

- SO_REUSEPORT (on Linux) or SO_REUSEPORT_LB (on FreeBSD 12.0+) on UDP and by choice on TCP

- Binding to non-local addresses (IP_FREEBIND on Linux, IP_BINDANY/IPV6_BINDANY on FreeBSD)

- Ignoring PMTU information for IPv4/UDP via IP_PMTUDISC_OMIT

## License

Knot DNS is licensed under the GNU General Public License v2.0 or later. The full text of the license is available in the `COPYING` file distributed with the source code.