dns-extensions.tex

   1 \subsection{Extensions to the DNS protocol}
   2
   3 \subsubsection{Multicast DNS}
   4 \term{Multicast DNS}~\cite{rfc6762} (mDNS) describes an extension of the Domain Name
   5 System that allows DNS resource records to be distributed on multiple hosts in a
   6 network, therefore avoiding the need of a central server.
   7
   8 Software that supports resolution of mDNS records listens on the reserved
   9 link-local multicast address \code{224.0.0.251} (for IPv4 queries) or
  10 \code{FF02::FB} (for IPv6 queries) on UDP port 5353 for incoming queries.
  11 Queries sent to those multicast address and port are standard DNS queries, and
  12 if a host receiving a query knows about the queried resource, it responds to the
  13 querying host with a standard DNS response. The querying host can then simply
  14 finish and use the result, or wait until other hosts respond to its query. The
  15 latter is typically the case when querying for \code{SRV} records to obtain a
  16 list of services which are present in the network.
  17
  18 Another feature of Multicast DNS is the reduction of traffic through
  19 \term{Known-Answer Suppression}. It allows a querying host to specify already
  20 known resources in its query when querying resources that could exist on more
  21 than one host (e.~g., SRV records). The hosts matching those resources then do
  22 not generate a response.
  23
  24 Finally, hosts may also send unsolicited responses. This can be used to notify
  25 the network of new services available on the host.
  26
  27 \pages{1}
  28
  29 \subsubsection{DNS-Based Service Discovery}
  30 \todo
  31 \term{DNS-based Service Discovery} \cite{rfc6763}
  32 \begin{itemize}
  33         \item allows flexible mapping of available services to ports
  34         \item utilization of SRV \cite{rfc2782}, TXT and PTR records
  35         \item case study for IoT in \cite{Klauck:2012:BCC:2352852.2352881}
  36 \end{itemize}
  37
  38 \pages{1}
  39 % vim: set ft=tex et ts=2 sw=2 :