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Timeout with MTU > 1232 after upgrading Connection + Hardware
![[de]](/s/countries/de.gif) Shadow Hawkins on Thursday, 21 May 2015 09:15:20
Good morning,
I'm having a strange issue with my IPv6 tunnel and I hope one of you
maybe has a solutions:
Yesterday my Cable-ISP (Unitymedia) upgraded my internet connection
(from the speed of 150mbit to 200mbit) and I have received a new
router with integrated cable-modem (AVM Fritz!Box 6490).
Installation and configuration went smooth, at least until I enabled
IPv6 support and chose "SixXS tunnel" in the options while supplying
my credentials. The connection to my tunnel is established and everyting
*looks* fine, BUT I cannot connect to any IPv6 enabled websites nor
can I just ping them.
The web browser (tested IE, Chrome, FireFox - latest versions) just loads
forever and a day while trying to ping several websites produces "timeout"
for any packet size larger than 1232...
I was using a Fritz!Box 6360 before and had no problems at all with
exactly the same settings I am using in the 6490 now...
As I didn't change anything on my PC and my tunnel worked perfectly before
the upgrade I do suspect the problem being either the new FritzBox or
something is wrong with my internet connection.
Some details:
ISP: Unitymedia (Cable) - native IPv4 - Fritz!Box 6490 - FritzOS 6.20
User: SME18-SIXXS - Tunnel: T166189 - PoP: dedus01 - Type: heartbeat
I've tried with default MTU of 1280 and with MTU 1480 on both ends (FritzBox and tunnel), same result.
Any ideas would be appreciated!
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Thursday, 21 May 2015 09:21:24
I've just noticed this:
ICMPv4 Errors Received 7, last: 81.210.132.206 2015-05-20 20:20:16 (1432153216; 0 days 12:49:51 ago)
I am 100%ly sure that the value of "ICMPv4 Errors Received" was "none"
before the connection and hardware upgrade/change.
Maybe that's the problem? Any ideas? Thanks!
Timeout with MTU > 1232 after upgrading Connection + Hardware
If you do not send any heartbeats:
Tunnel State : down
Tunnel Type : heartbeat
Last Heartbeat : 2015-05-20 20:18:30 (1432153110; 0 days 13:11:36 ago)
you won't get any connectivity either.
Hence, a traceroute6 is a good diagnostic to check from what you are getting IPv6 connectivity. Not through that tunnel from the above.
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Thursday, 21 May 2015 09:53:13
I've disabled the tunnel in the FritzBox options after not
being able to browse any IPv6 enabled website and didn't
re-enable it yet, so the time of the last heartbeat (around 12 hours ago)
is correct.
I'll re-enabled it when I get home in the afternoon and will try
a traceroute.
Thanks for your reply!
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Thursday, 21 May 2015 18:35:05
Hi again,
for some reason I can suddenly ping IPv6 enabled websites
and a trace is (almost) successful as well as long as I don't
use the "round trip path" option for the commands:
ping
tracert
With the "round trip path" option I just get timeouts all the way:
ping_r
tracert_r
Here's what "ipconfig /all" says about my connection:
ipconfig_all
I'm using Windows 7 Pro x64, fully updated btw.
Could any other information about my system be helpful?
Thanks in advance!
Timeout with MTU > 1232 after upgrading Connection + Hardware
You need to start looking at the settings on your tunnel endpoint.
Check that the MTU is configured correctly there is the most important bit.
That you get errors from routers towards you:
ICMPv4 Errors Received : 16, last: 81.210.132.206 2015-05-21 18:30:41 (1432233041; 0 days 00:16:14 ago)
is quite interesting, but could be anything.
After that, wireshark is likely your best next step.
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Thursday, 21 May 2015 18:41:33
I forgot to mention the most important thing:
I still cannot use a web browser to display websites via IPv6,
it takes ages, same problem for SSH and ftp connection to my linux server...
P.S.:
Sorry for the triple post,
being able to edit your own posts would be great! ;-)
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Thursday, 21 May 2015 19:41:42
I've checked my tunnel and it's set to an MTU of 1280,
same for my Fritz!Box, Windows reports 1280 for IPv6 on my
interface as well.
It's 1500 for IPv4, but that shouldn't be a problem, should it?
I've downloaded, installed and started wireshark. Unfortunately
I really have no idea what those thousands of nicely colored lines
of text
(that it shows me after running for a few minutes while I tried to
surf sixxs.net, my own ipv6 website and google)
should tell me.
I guess I'll just give up right here, I'd like to "buy you a beer" anyways,
how can I do that?
Timeout with MTU > 1232 after upgrading Connection + Hardware
Windows reports 1280 for IPv6 on my interface as well.
That sounds wrong. As your local interface is likely Ethernet and that has an MTU of 1500 (or even larger with Jumboframes)
It's 1500 for IPv4, but that shouldn't be a problem, should it?
You are effectively crippling your local network's IPv6 experience.
Some people wrongly "recommend" setting it to 1280 as then you avoid MTU issues, but as those issues are caused by remote sites that are broken, why let them determine that your local network has to have smaller packets. Especially considering they are the ones breaking the RFCs by ignoring ICMPv6 Packet Too Big (and likely every other ICMP message).
UnfortunatelyI really have no idea what those thousands of nicely colored lines of text
The important ones are the red ones, as they indicate problematic ones.
The output should be quite explanatory. There are various rather good tutorials on the Internet which explain what everything is. And it will also give you a deeper understanding of things.
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Friday, 22 May 2015 07:50:28
Hi again,
I've set the MTU on my ethernet interface to 1492 for IPv6 (I've read that this would be a good value on several websites...) and rebooted my pc and my
Fritz!Box (just to be sure), unfortunately nothing has changed, so I took
a closer look at what wireshark gave me.
Like you suggested I looked for the red lines and I noticed ALOT
(and I mean hundreds!) of TCP Retransmissions and several TCP RSTs,
so for some reason the connection seems to be in kind of a reset loop....
Timeout with MTU > 1232 after upgrading Connection + Hardware
I've set the MTU on my ethernet interface to 1492 for IPv6 (I've read that this would be a good value on several websites...)
Why would 1492 be a "good" one?
Ethernet has an MTU 1500 (or higher if Jumboframes are in use) as such 1500 is the correct MTU.
Path MTU Discovery will make the packets going over the tunnel limit themselves to whatever the MTU of the tunnel is. But your local network is still 1500.
On Windows the 'tracert' command should show Path MTU btw.
and rebooted my pc and my Fritz!Box (just to be sure), unfortunately nothing has changed,
Checking the actual running configuration is the thing to do here.
And you need to do that on all the hops: your PC and your tunnel box.
so I took a closer look at what wireshark gave me. Like you suggested I looked for the red lines and I noticed ALOT (and I mean hundreds!) of TCP Retransmissions and several TCP RSTs, so for some reason the connection seems to be in kind of a reset loop....
That is because those packets are not being delivered (dropped somewhere) and thus the TCP stack keeps on trying to send them.
What you should check though if you are seeing any ICMPv6 traffic stating that Packets Are Too Big. Your Fritz!Box, which terminates the tunnel, should send one directly for each packet as the tunnel interface is much smaller than the MTU of your Ethernet.
Oh and have fun digging in Wireshark, it is a great learning and debugging tool.
Timeout with MTU > 1232 after upgrading Connection + Hardware
Shadow Hawkins on Friday, 22 May 2015 18:34:37
Hi again,
I've changed the MTU to 1500, but that didn't change anything.
After searching and searching I've found a thread in an unoffical
support forum of my ISP. There's a bunch of others with the same
problem, all are using the FB 6490 and most of them used a FB 6360
before and had no problems at all. Just like it happened to me, their
problems started after upgrading to FB 6490....
As Unitymedia is enforcing the firmware version, we are all on the same (6.20)
and some people already guessed that this version is bugged regarding IPv6
connectivity (at least via tunnels).
So I'm finally giving up on this until there's a new firmware.
Many thanks for your help and this great service.
P.S.: I still would like to donate a few bucks to the cause, PayPal available?
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![[ch]](/s/countries/ch.gif)
on Thursday, 21 May 2015 09:32:57
Posting is only allowed when you are 
