\term{Multicast DNS} (mDNS)~\cite{rfc6762} describes an extension to the Domain
Name System that allows DNS resource records to be distributed on multiple hosts
in a network, therefore avoiding central authorities and enabling every host to
\term{Multicast DNS} (mDNS)~\cite{rfc6762} describes an extension to the Domain
Name System that allows DNS resource records to be distributed on multiple hosts
in a network, therefore avoiding central authorities and enabling every host to
-publish its own entries. For that purpose, a special domain, usually
-named \code{.local}, is used.
+publish its own entries. For that purpose, a special top-level domain, is used,
+usually named \code{.local}, which contains those entries.
Software that supports mDNS listens on the reserved
link-local multicast address \code{224.0.0.251} (for IPv4 queries) or
Software that supports mDNS listens on the reserved
link-local multicast address \code{224.0.0.251} (for IPv4 queries) or
Queries sent to those multicast address and port are standard DNS queries.
If a host receives a query and knows about the queried resource, it responds to the
querying host with a standard DNS response. The querying host can then simply
finish and use the result, or wait until other hosts respond to its query. The
latter is typically the case when a record can have multiple values, as it is
Queries sent to those multicast address and port are standard DNS queries.
If a host receives a query and knows about the queried resource, it responds to the
querying host with a standard DNS response. The querying host can then simply
finish and use the result, or wait until other hosts respond to its query. The
latter is typically the case when a record can have multiple values, as it is
Another feature of Multicast DNS is the reduction of traffic through
\term{Known-Answer Suppression}. It allows a querying host to specify already
known resources in its query when querying resources that could exist on more
Another feature of Multicast DNS is the reduction of traffic through
\term{Known-Answer Suppression}. It allows a querying host to specify already
known resources in its query when querying resources that could exist on more
not generate a response, thus reducing the messages in the network and saving
bandwidth, which is usually a scarce resource in wireless networks.
not generate a response, thus reducing the messages in the network and saving
bandwidth, which is usually a scarce resource in wireless networks.
As another recent extension for the Domain Name System, \term{DNS-Based Service
Discovery (DNS-SD)}~\cite{rfc6763} uses DNS records of types
As another recent extension for the Domain Name System, \term{DNS-Based Service
Discovery (DNS-SD)}~\cite{rfc6763} uses DNS records of types
-SRV~\cite{rfc2782} and PTR in a way that allows hosts to browse
-for services in a domain. This is a two-step process, consisting of
+SRV~\cite{rfc2782} and PTR~\cite{rfc1035} in a way that allows hosts to browse
+for services in a domain. While SRV records specify the location of services on
+a host, PTR records hold a reverse mapping from IP address to host name.
+DNS-SD now relies on a two-step process, consisting of
\term{Service Instance Enumeration} and \term{Service Instance Resolution}.
\paragraph{1. Service Instance Enumeration} At first, to enumerate the available
\term{Service Instance Enumeration} and \term{Service Instance Resolution}.
\paragraph{1. Service Instance Enumeration} At first, to enumerate the available
projects / skm-ma-ws1314.git / blobdiff