why this tip works ?

Hi all,

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

http://www.youtube.com/watch?v=Sd8nHsUevAY

annalissa wrote:
> can any one explain to me why the tip given below works ?
>
> http://www.youtube.com/watch?v=Sd8nHsUevAY

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.

Hello,

Allen Kistler a écrit :
> annalissa wrote:
>> can any one explain to me why the tip given below works ?
>>
>> http://www.youtube.com/watch?v=Sd8nHsUevAY

This is Usenet. Please don't rely on the readers' ability to watch Flash
videos !

> 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.

Thank you Allen.

> 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.

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.

> 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.

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.

> 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.

Things are changing. See <http://www.google.com/intl/en/ipv6/>.