dns.xml

<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
      xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
      xml:id="dns">
  <title>DNS setup</title>

  <para>The DNS records to be created are detailed in
  <xref linkend="dns-records-for-example"/></para>

  <table xml:id="dns-records-for-example">
    <title>DNS records for the example</title>
    <tgroup cols="3">
      <colspec colname="c1" colnum="1" colwidth="2*" />
      <colspec colname="c2" colnum="2" colwidth="1*" />
      <colspec colname="c3" colnum="3" colwidth="3*" />

      <thead>
        <row>
          <entry align="center">Record Name</entry>
          <entry align="center">Type</entry>
          <entry align="center">Value</entry>
        </row>
      </thead>

      <tbody>
        <row>
          <entry><literal>server1</literal></entry>
          <entry><literal>A</literal></entry>
          <entry><literal>198.51.100.19</literal></entry>
        </row>
        <row>
          <entry><literal>server1</literal></entry>
          <entry><literal>AAAA</literal></entry>
          <entry><literal>2001:DB8:1000:2000::19</literal></entry>
        </row>
        <row>
          <entry><literal>turn-server</literal></entry>
          <entry><literal>A</literal></entry>
          <entry><literal>198.51.100.19</literal></entry>
        </row>
        <row>
          <entry><literal>turn-server</literal></entry>
          <entry><literal>AAAA</literal></entry>
          <entry><literal>2001:DB8:1000:2000::19</literal></entry>
        </row>
        <row>
          <entry><literal>sip-proxy</literal></entry>
          <entry><literal>A</literal></entry>
          <entry><literal>198.51.100.19</literal></entry>
        </row>
        <row>
          <entry><literal>sip-proxy</literal></entry>
          <entry><literal>AAAA</literal></entry>
          <entry><literal>2001:DB8:1000:2000::19</literal></entry>
        </row>
        <row>
          <entry><literal>xmpp-gw</literal></entry>
          <entry><literal>A</literal></entry>
          <entry><literal>198.51.100.19</literal></entry>
        </row>
        <row>
          <entry><literal>xmpp-gw</literal></entry>
          <entry><literal>AAAA</literal></entry>
          <entry><literal>2001:DB8:1000:2000::19</literal></entry>
        </row>
        <row>
          <entry><literal>_stun._udp</literal></entry>
          <entry><literal>SRV</literal></entry>
          <entry><literal>0 1 3478 turn-server.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>_turn._udp</literal></entry>
          <entry><literal>SRV</literal></entry>
          <entry><literal>0 1 3478 turn-server.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>_sips._tcp</literal></entry>
          <entry><literal>SRV</literal></entry>
          <entry><literal>0 1 5061 sip-proxy.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>_xmpp-client._tcp</literal></entry>
          <entry><literal>SRV</literal></entry>
          <entry><literal>5 0 5222 xmpp-gw.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>_xmpp-server._tcp</literal></entry>
          <entry><literal>SRV</literal></entry>
          <entry><literal>5 0 5269 xmpp-gw.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>@</literal></entry>
          <entry><literal>NAPTR</literal></entry>
          <entry><literal>10 0 "s" "SIPS+D2T" "" _sips._tcp.example.org.</literal></entry>
        </row>
        <row>
          <entry><literal>@</literal></entry>
          <entry><literal>NAPTR</literal></entry>
          <entry><literal>10 0 "s" RELAY:turn.udp "" _turn._udp.example.org.</literal></entry>
        </row>
      </tbody>
    </tgroup>
  </table>

  <sect1 xml:id="dns-non-standard-ports">
    <title>Using non-standard ports</title>
    <para>RTC makes use of DNS SRV records for load-balancing and failover.
    A key feature of the SRV record is that the TCP or UDP port number is
    specified in the record.  <xref linkend="dns-records-for-example"/>
    demonstrates the use of standard port numbers for SIP, TURN and
    XMPP.</para>

    <para>If users are connecting to the service from arbitrary locations,
    including public wi-fi hotspots, hotels and the offices of other companies,
    they will almost certainly encounter firewalls that only allow traffic
    to pass on a limited range of port numbers or through HTTP proxy
    servers.</para>

    <para>For this reason, it is common to operate RTC services on port
    443 instead of the normal port numbers.  Two or more processes can't
    listen on the same port number on the same IP address.  When all the
    RTC processes have to use port 443, it is necessary to have a different
    IP address for each process.
    <xref linkend="dns-non-standard-ports-example"/> gives a summary of
    the ports to change.</para>

    <table xml:id="dns-non-standard-ports-example">
      <title>Protocols using port 443</title>
      <tgroup cols="3">
        <colspec colname="c1" colnum="1" colwidth="2*" />
        <colspec colname="c2" colnum="2" colwidth="1*" />
        <colspec colname="c3" colnum="3" colwidth="1*" />

        <thead>
          <row>
            <entry align="center">Protocol</entry>
            <entry align="center">Default port</entry>
            <entry align="center">Non-standard port</entry>
          </row>
        </thead>

        <tbody>
          <row>
            <entry>STUN / TURN over TLS</entry>
            <entry>5349</entry>
            <entry>443</entry>
          </row>
          <row>
            <entry>SIP over TLS</entry>
            <entry>5061</entry>
            <entry>443</entry>
          </row>
          <row>
            <entry>XMPP client</entry>
            <entry>5222</entry>
            <entry>443</entry>
          </row>
        </tbody>
      </tgroup>
    </table>
  </sect1>

  <sect1 xml:id="dns-sample-zone">
    <title>Sample DNS zone file</title>
    <para>See <xref linkend="dns-bind-example-zone"/> for an example of
    how to write the entries for the zone file.  For the purposes of the
    example, this file would be <code>/etc/bind/db.example.org</code> on
    the nameserver host.</para>

    <example xml:id="dns-bind-example-zone">
      <title>ISC Bind zone file entries</title>
      <programlisting format="linespecific">; the server where everything will run
server1            IN     A      198.51.100.19
server1            IN     AAAA   2001:DB8:1000:2000::19

; Use different names for each service.
; Don't use CNAMEs, the SRV records (further down)
; can't point to CNAME records.
turn-server        IN     A      198.51.100.19
turn-server        IN     AAAA   2001:DB8:1000:2000::19
sip-proxy          IN     A      198.51.100.19
sip-proxy          IN     AAAA   2001:DB8:1000:2000::19
xmpp-gw            IN     A      198.51.100.19
xmpp-gw            IN     AAAA   2001:DB8:1000:2000::19


; DNS SRV for STUN / TURN
_stun._udp  IN SRV    0 1 3478 turn-server.example.org.
_turn._udp  IN SRV    0 1 3478 turn-server.example.org.

; DNS SRV and NAPTR records for SIP
_sips._tcp  IN SRV    0 1 5061 sip-proxy.example.org.
@           IN NAPTR  10 0 "s" "SIPS+D2T" "" _sips._tcp.example.org.
@           IN NAPTR  10 0 "s" RELAY:turn.udp "" _turn._udp.example.org.

; DNS SRV records for XMPP Server and Client modes:
_xmpp-client._tcp  IN     SRV    5 0 5222 xmpp-gw.example.org.
_xmpp-server._tcp  IN     SRV    5 0 5269 xmpp-gw.example.org.</programlisting>
    </example>
  </sect1>

  <sect1 xml:id="dns-testing">
    <title>Testing the DNS settings</title>

    <para>Use the <code>dig</code> command to test, as demonstrated in
    <xref linkend="dns-dig-example"/></para>

    <example xml:id="dns-dig-example">
      <title>Inspecting DNS entries with <code>dig</code></title>
      <programlisting format="linespecific">$ dig -t naptr +short example.org
10 0 "s" "SIPS+D2T" "" _sips._tcp.example.org.

$ dig -t srv +short _sips._tcp.example.org.
0 1 5061 sip-proxy.example.org.</programlisting>
    </example>

  </sect1>

</chapter>