why this tip works ?

Discussion in 'Linux Networking' started by annalissa, Feb 15, 2009.

  1. annalissa

    annalissa Guest

    Hi all,

    can any one explain to me why the tip given below works ?

     
    annalissa, Feb 15, 2009
    #1
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  2. For the benefit of others, the tip is to alias net-pf-10 (network
    protocol family 10, BTW) to off in /etc/modprobe.d/aliases to speed up
    an Internet connection for Ubuntu.

    It works because it prevents the ipv6 kernel module from loading, hence
    disabling any support for IPv6.

    Personally, I think a better way, if that's what you want to do, is put
    "install ipv6 /bin/true" in /etc/modprobe.conf. Don't screw with the
    aliases.

    What not loading ipv6 does is keep your machine from requesting IPv6 DNS
    records (AAAA) from your DNS server. Some DNS servers ignore requests
    for IPv6 addresses, which means the client has to time out the request
    before it asks for an IPv4 address (A). (If it retries, then it has to
    time out all the retries, which could be half a minute or so.) Most DNS
    servers are well-behaved enough now that they'll return an invalid
    request result or an unknown result if they don't support IPv6 requests,
    so the client can make an IPv4 request right away. In other words, for
    most people this tip isn't going to improve anything.

    FWIW, Google did some initial testing a year or so ago that found a
    different, but related, problem. If the client is IPv6-enabled, but the
    Internet connection is IPv4-only, requesting *and*getting* an IPv6
    address for a site makes the site completely inaccessible. That's why
    they didn't assign an IPv6 address to www.google.com, but instead
    created a different name (ipv6.google.com) that probably points to the
    same pool of servers.
     
    Allen Kistler, Feb 15, 2009
    #2
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  3. Hello,

    Allen Kistler a écrit :
    This is Usenet. Please don't rely on the readers' ability to watch Flash
    videos !
    Thank you Allen.
    Personnally, I think an even better way is to fix those broken DNS
    resolvers out there. Actually most of the ones I have heard about are
    the DNS proxy embedded in some SOHO "routers", and you do not have to
    use it.
    This is not quite exact. Google said in
    <http://www.google.com/intl/en/ipv6/faq.html> :
    ======================================================================
    Why not just enable IPv6 on Google websites?

    We continuously conduct detailed measurements on the quality of IPv6
    connectivity, and our latest results show that making Google services
    generally available over IPv6 at this time would lead to connection
    problems and increased latency for a small number of users. User
    experience is very important to us, and we do not want to impact users
    on networks that do not yet fully support IPv6. We will continue to
    re-evaluate the situation as the IPv6 Internet evolves.
    ======================================================================

    There are lots of IPv6-enabled hosts without global IPV6 connectivity
    out there. This includes many hosts running GNU/Linux or Windows Vista.
    If what you wrote were right, *all* these hosts could not reach
    dual-stack sites, which is fortuntely not the case.

    If the client is IPv6-enabled but the host it runs on has no global IPv6
    connectivity (i.e. no default IPv6 route or no global address), then
    non-local IPv6 communications are rejected with a "network unreachable"
    error, and the client tries again using IPv4.

    Only hosts with a broken IPv6 setup, e.g. a default IPv6 route but no
    good IPv6 connectivity, will experience trouble. This is the "small
    number of users" Googles talks about.
    Things are changing. See <http://www.google.com/intl/en/ipv6/>.
     
    Pascal Hambourg, Feb 15, 2009
    #3
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