I can fetch the header of websites via IPv6 but not the webpage, why?

[Ez Egy]

As I said:

1) "I have a native IPv6 connection on my Desktop behind my router." -> So
there is no tunnel. Only native IPv6 that the Hungarian telekom.hu gives.
2) We will try out setting manually the MSS to 1392, hopefully that could
be a good workaround.
3) We will try out the site: http://netalyzr.icsi.berkeley.edu/

I will post the status here later, Thanks!



On Mon, Jan 20, 2014 at 11:59 AM, Tore Anderson <tore at fud.no> wrote:

> * Ez mail
>
> > Since I have no fr**king clue what could the problem be, I'm trying on
> > this list :)
>
> I concur 100% with Erik's assessment that this in all likelihood is a
> PMTUD problem, specifically in the web_server->your_desktop direction.
>
> I'd just like to add that the fact that you see it happening to several
> independent websites that are known to be operated by competent staff,
> and that the problem comes and goes, further indicates that it is due to
> rate-limiting of ICMPv6 PTB replies from your tunnel broker's tunneling
> router/server.
>
> The ICSI Netalyzr (http://netalyzr.icsi.berkeley.edu/) will give you
> very useful debugging output from the outside point of view. You might
> have to run it a few times to to reveal the MTU blackhole though, due to
> the problem's intermittent nature.
>
> As Erik mentions, lowering the TCP MSS will likely work around the
> problem. You can probably do this by having the RAs your router emits to
> the LAN advertise an MTU of 1452 to match your tunnel (which in turn
> should make your desktop default to a TCP MSS of 1392), and/or have your
> router rewrite ("clamp") the MSS value in TCP packets it forwards
> to/from the tunnel to 1392.
>
> Or, even better, get rid of the tunneling crap and get native IPv6. This
> is a very common problem for IPv6 tunnels. As a web site operator I
> would actually prefer it if people stayed IPv4-only until their ISP
> could provide them with properly supported IPv6 connectivity. Oh well...
>
> Tore
>
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