                                  DNS over TCP

   MaraDNS 1.2 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 = "/opt/local/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 /opt/local/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 = "/opt/local/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 = "/opt/local/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.
