# DNS over TCP

MaraDNS has full support for DNS over TCP. However, this setup is not automatically done; a little configuration needs to be set up and the "zoneserver" daemon has to be running in addition to the MaraDNS daemon in order for DNS records to be served over TCP.

The first mararc variable that needs to be set is `tcp_convert_acl`. This is a list of IPs that are allowed to make DNS-over-TCP queries. In the case of using MaraDNS as an authoritative nameserver, this should have a value of "0.0.0.0/0" (anyone on the internet can make TCP DNS connections). If MaraDNS is being used as a recursive or upstream server, this should have the same value that the `recursive_acl` mararc variable has. In the case of MaraDNS being both a recursive and authoritative DNS server, `tcp_convert_acl` should have a value of "0.0.0.0/0"--this is not a security hazard since the zoneserver will only send UDP packets that request recursion if the client that connects to the TCP server is on the `recursive_acl` list.

The second mararc variable that needs to be set is `tcp_convert_server`. This is the IP of the UDP DNS server that we will connect whenever we get a DNS-over-TCP request. The way we perform DNS over TCP is as follows:

- The resolver or end user connects via TCP to the `zoneserver` daemon.
- The resolver sends a DNS query over TCP.
- The `zoneserver` program converts the query in to a UDP query.
- `zoneserver` sends the UDP query to the ip specified in the `tcp_convert_server` mararc variable.
- `zoneserver` waits for a UDP reply
- After `zoneserver` gets a UDP reply, it converts this reply to a TCP reply to give to the resolver/end user.

This is what a mararc file which serves the domain `example.com` and will provide both DNS over UDP and TCP will look like:

    ipv4_bind_addresses = "10.1.2.3"
    chroot_dir = "/etc/maradns"
    csv2 = {}
    csv2["example.com."] = "db.example.com"
    tcp_convert_acl = "0.0.0.0/0"
    tcp_convert_server = "10.1.2.3"

With this mararc file, and the csv2 zone file "db.example.com" in the directory `/etc/maradns`, the program `maradns` will process UDP DNS queries, and `zoneserver` will process TCP DNS queries. `maradns` is a standalone UDP DNS server; `zoneserver` is a TCP proxy that converts TCP requests in to UDP requests. Both daemons must be running to process both UDP and TCP DNS queries.

This is what a recursive mararc file which provides recursive DNS over TCP and UDP will look like:

    ipv4_bind_addresses = "10.1.2.3"
    chroot_dir = "/etc/maradns"
    recursive_acl = "10.0.0.0/8"
    tcp_convert_acl = "10.0.0.0/8"
    tcp_convert_server = "10.1.2.3"

If both `maradns` and `zoneserver` are running, this mararc file will provide recursive DNS for anyone with an IP starting with the number "10" (this is a special network for private IPs) on a machine with the IP 10.1.2.3.

## Long packets

`maradns`, the UDP DNS server, in compliance with RFC1035 section 2.3.4, will not output a packet longer than 512 bytes long. This is sufficient packet size for over 99% of the DNS traffic out there.

However, some DNS packets may need to be longer than this. MaraDNS has support for outputting DNS packets up to 4096 bytes long. RFC1035 only allows such packets to be sent over TCP; the work around is to have the UDP server only send long RFC-violating DNS packets to the TCP server; which then converts the long UDP packet in to a RFC-compliant long TCP packet.

Since these packets use extra memory to store in memory, they are only enabled when MaraDNS is compiled as an authoritative-only DNS server.

To compile MaraDNS as an authoritative-only server:

- Compile MaraDNS as an authoritative-only nameserver:

      ./configure --authonly
      make

- Install MaraDNS as an authoritative-only nameserver:

      make install

- Make sure any existing copy of maradns with recursive support has been removed:

      rm /usr/sbin/maradns
      rm /usr/local/sbin/maradns

  (The authoritative-only binary has the name maradns.authonly)

At this point, one uses the `long_packet_ipv4` mararc variable to tell `maradns.authonly` which IPs we will send long UDP packets to. This value is usually the same value as is set for `ipv4_bind_addresses`.

`long_packet_ipv4` is a list of IPs `maradns.authonly` will send RFC-violating long UDP packets to. When `zoneserver` listens for a UDP reply from `maradns`, the `zoneserver` program will be able to process long UDP packets, converting them in to RFC-compliant TCP DNS packets.

Note that the `zoneserver` program, like the `maradns` program, is changed when compiled after `./configure --authonly`. These changes are needed for the zoneserver to accept long DNS packets.

This is what a `mararc` file which provides authoritative DNS over TCP and UDP, sending long UDP packets to the TCP server to process, will look like:

    ipv4_bind_addresses = "10.1.2.3"
    chroot_dir = "/etc/maradns"
    csv2 = {}
    csv2["example.com."] = "db.example.com"
    tcp_convert_acl = "0.0.0.0/0"
    tcp_convert_server = "10.1.2.3"
    long_packet_ipv4 = "10.1.2.3"

The `zoneserver` program can also be used to serve DNS zones; see the file dnsmaster for details.