sult} method is called when a response is received from one of
        C{clients}. Defaults to L{None} if no caches are specified. See
        C{caches} of L{__init__} for more details.
    @type cache: L{Cache<twisted.names.cache.CacheResolver>} or L{None}

    @ivar canRecurse: A flag indicating whether this server is capable of
        performing recursive DNS resolution.
    @type canRecurse: L{bool}

    @ivar resolver: A L{resolve.ResolverChain} containing an ordered list of
        C{authorities}, C{caches} and C{clients} to which queries will be
        dispatched.
    @type resolver: L{resolve.ResolverChain}

    @ivar verbose: See L{__init__}

    @ivar connections: A list of all the connected L{DNSProtocol} instances
        using this object as their controller.
    @type connections: C{list} of L{DNSProtocol} instances

    @ivar protocol: A callable used for building a DNS stream protocol. Called
        by L{DNSServerFactory.buildProtocol} and passed the L{DNSServerFactory}
        instance as the one and only positional argument.  Defaults to
        L{dns.DNSProtocol}.
    @type protocol: L{IProtocolFactory} constructor

    @ivar _messageFactory: A response message constructor with an initializer
         signature matching L{dns.Message.__init__}.
    @type _messageFactory: C{callable}
    Nr