# Addresses and services

Addresses, ports, protocols, and API calls available for clients communicating with resolver are configured using `net.listen()`.

First you need to decide what service should be available on given IP address + port combination.

Protocol/service | net.listen kind
--- | ---
DNS (unencrypted UDP+TCP, RFC 1034) | `dns`
DNS (unencrypted UDP, using XDP Linux API) | `xdp`
DNS-over-TLS (DoT) | `tls`
DNS-over-HTTPS (DoH) | `doh2`
Web management | `webmgmt`
Control socket | `control`
Legacy DNS-over-HTTPS (DoH) | `doh_legacy`

Note

By default, unencrypted DNS and DNS-over-TLS are configured to listen on localhost.

Control sockets are created either in `/run/knot-resolver/control/` (when using systemd) or `$PWD/control/`.

net.listen(addresses[, port = 53, { kind = 'dns', freebind = false }])
  Returns:

    `true` if port is bound, an error otherwise

  Listen on addresses; port and flags are optional. The addresses can be specified as a string or device. Port 853 implies `kind = 'tls'` but it is always better to be explicit. Freebind allows binding to a non-local or not yet available address.

Network protocol | Configuration command
--- | ---
DNS (UDP+TCP, RFC 1034) | `net.listen('192.0.2.123', 53)`
DNS (UDP, using XDP) | `net.listen('192.0.2.123', 53, { kind = 'xdp' })`
DNS-over-TLS (DoT) | `net.listen('192.0.2.123', 853, { kind = 'tls' })`
DNS-over-HTTPS (DoH) | `net.listen('192.0.2.123', 443, { kind = 'doh2' })`
Web management | `net.listen('192.0.2.123', 8453, { kind = 'webmgmt' })`
Control socket | `net.listen('/tmp/kres.control', nil, { kind = 'control' })`

Examples:

>     net.listen('::1')
>     net.listen(net.lo, 53)
>     net.listen(net.eth0, 853, { kind = 'tls' })
>     net.listen('192.0.2.1', 53, { freebind = true })
>     net.listen({'127.0.0.1', '::1'}, 53, { kind = 'dns' })
>     net.listen('::', 443, { kind = 'doh2' })
>     net.listen('::', 8453, { kind = 'webmgmt' }) -- see http module
>     net.listen('/tmp/kresd-socket', nil, { kind = 'webmgmt' }) -- http module supports AF_UNIX
>     net.listen('eth0', 53, { kind = 'xdp' })
>     net.listen('192.0.2.123', 53, { kind = 'xdp', nic_queue = 0 })

Warning

On machines with multiple IP addresses avoid listening on wildcards `0.0.0.0` or `::`. Knot Resolver could answer from different IP addresses if the network address ranges overlap, and clients would probably refuse such a response.

## PROXYv2 protocol

Knot Resolver supports proxies that utilize the PROXYv2 protocol to identify clients.

A PROXY header contains the IP address of the original client who sent a query. This allows the resolver to treat queries as if they actually came from the client’s IP address rather than the address of the proxy they came through. For example, Views and ACLs are able to work properly when PROXYv2 is in use.

Since allowing usage of the PROXYv2 protocol for all clients would be a security vulnerability, because clients would then be able to spoof their IP addresses via the PROXYv2 header, the resolver requires you to specify explicitly which clients are allowed to send PROXYv2 headers via the `net.proxy_allowed()` function.

PROXYv2 queries from clients who are not explicitly allowed to use this protocol will be discarded.

net.proxy_allowed([addresses])

  Allow usage of the PROXYv2 protocol headers by clients on the specified `addresses`. It is possible to permit whole networks to send PROXYv2 headers by specifying the network mask using the CIDR notation (e.g. `172.22.0.0/16`). IPv4 as well as IPv6 addresses are supported.

  If you wish to allow all clients to use PROXYv2 (e.g. because you have this kind of security handled on another layer of your network infrastructure), you can specify a netmask of `/0`. Please note that this setting is address-family-specific, so this needs to be applied to both IPv4 and IPv6 separately.

  Subsequent calls to the function overwrite the effects of all previous calls. Providing a table of strings as the function parameter allows multiple distinct addresses to use the PROXYv2 protocol.

  When called without arguments, `net.proxy_allowed` returns a table of all addresses currently allowed to use the PROXYv2 protocol and does not change the configuration.

Examples:

>     net.proxy_allowed('172.22.0.1')    -- allows '172.22.0.1' specifically
>     net.proxy_allowed('172.18.1.0/24') -- allows everyone at '172.18.1.*'
>     net.proxy_allowed({
>             '172.22.0.1', '172.18.1.0/24'
>     })                                 -- allows both of the above at once
>     net.proxy_allowed({ 'fe80::/10' }  -- allows everyone at IPv6 link-local
>     net.proxy_allowed({
>             '::/0', '0.0.0.0/0'
>     })                                 -- allows everyone
>     net.proxy_allowed('::/0')          -- allows all IPv6 (but no IPv4)
>     net.proxy_allowed({})              -- prevents everyone from using PROXYv2
>     net.proxy_allowed()                -- returns a list of all currently allowed addresses

## Features for scripting

Following configuration functions are useful mainly for scripting or Run-time reconfiguration.

net.close(address[, port])
  Returns:

    boolean (at least one endpoint closed)

  Close all endpoints listening on the specified address, optionally restricted by port as well.

net.list()
  Returns:

    Table of bound interfaces.

  Example output:

      [1] => {
          [kind] => tls
          [transport] => {
              [family] => inet4
              [ip] => 127.0.0.1
              [port] => 853
              [protocol] => tcp
          }
      }
      [2] => {
          [kind] => dns
          [transport] => {
              [family] => inet6
              [ip] => ::1
              [port] => 53
              [protocol] => udp
          }
      }
      [3] => {
          [kind] => dns
          [transport] => {
              [family] => inet6
              [ip] => ::1
              [port] => 53
              [protocol] => tcp
          }
      }
      [4] => {
          [kind] => xdp
          [transport] => {
              [family] => inet4+inet6
              [interface] => eth2
              [nic_queue] => 0
              [port] => 53
              [protocol] => udp
          }
      }

net.interfaces()
  Returns:

    Table of available interfaces and their addresses.

  Example output:

      [lo0] => {
          [addr] => {
              [1] => ::1
              [2] => 127.0.0.1
          }
          [mac] => 00:00:00:00:00:00
      }
      [eth0] => {
          [addr] => {
              [1] => 192.168.0.1
          }
          [mac] => de:ad:be:ef:aa:bb
      }

  Tip

  You can use `net.<iface>` as a shortcut for specific interface, e.g. `net.eth0`

net.tcp_pipeline([len])

  Get/set per-client TCP pipeline limit, i.e. the number of outstanding queries that a single client connection can make in parallel. Default is 100.

      > net.tcp_pipeline()
      100
      > net.tcp_pipeline(50)
      50

  Warning

  Please note that too large limit may have negative impact on performance and can lead to increased number of SERVFAIL answers.