Results from Boost.Asio Amplifier Differ

I have a canning loudspeaker calling boost::asio::ip::tcp::resolver::resolve()on localhostonce every 5 seconds. It counts the number of returned endpoints and compares this value with the previous iteration.

#include <boost/asio.hpp>

#include <iostream>

int main(int argc, char *argv[])
{
    if ( argc < 3 ) {
        std::cerr << argv[0] << " host port" << std::endl;
        exit( EXIT_FAILURE );
    }
    const char* host = argv[1];
    const char* service = argv[2];

    boost::asio::io_service io_service;
    boost::asio::ip::tcp::resolver resolver( io_service );

    size_t previous = 0;
    while ( true ) {
        boost::asio::ip::tcp::resolver::iterator i(
                resolver.resolve(
                    boost::asio::ip::tcp::resolver::query( host, service )
                    )
                );
        size_t count( 0 );
        while ( i != boost::asio::ip::tcp::resolver::iterator() ) {
            std::cout << i->endpoint() << std::endl;
            ++i;
            ++count;
        }

        std::cout << "got " << count << " addresses" << std::endl;
        if ( previous == 0 ) {
            previous = count;
        }
        assert( count == previous );

        sleep( 5 );
    }
}

trial session

~> time ./addrinfo_asio localhost 80

...

127.0.0.1:80
got 1 addresses
[::1]:80
127.0.0.1:80
got 2 addresses
addrinfo_asio: addrinfo_asio.cc:35: int main(int, char**): Assertion `count == previous' failed.
Aborted (core dumped)

real    216m20.515s
user    0m0.181s
sys     0m0.193s
~> 

You can see that he found one endpoint (127.0.0.1:80) for about 3.5 hours, then he found two (127.0.0.1:80 and [:: 1]: 80). I'm interested

• why does the number of endpoints change from one to two?
• what can cause this?

ipv4 ipv6 , ipv4. , , , asio, , getaddrinfo , . - ppc64 RHEL 6.2, . .