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How come a:

curl -v -6 http://badurl.com

doesn't work but a:

curl -v -6 --head http://badurl.com

Perfectly works?

MTU isn't the problem (?) since:

root@server:~# ping6 -c 10 -s 2000 -M do IPV6ADDRESSOFBADURL.COM
PING IPV6ADDRESSOFBADURL.COM(IPV6ADDRESSOFBADURL.COM)
2000 data bytes From IPV6ADDRESSOFSOMEGATEWAY icmp_seq=1 Packet too big: mtu=1452
2008 bytes from IPV6ADDRESSOFBADURL.COM: icmp_seq=2 ttl=54 time=82.5 ms
2008 bytes from IPV6ADDRESSOFBADURL.COM: icmp_seq=3 ttl=54 time=82.4 ms

tcpdump shows that if the IPv6 connection is bad then my Desktop doesn't receives anything..ip6tables is empty.

My question: WHY does the connection "randomly gets bad" from my Desktop machine that has native IPv6 address to IPv6 enabled websites? (problem occurs not just on one site)

Or any hints, how to debug this?

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closed as off-topic by Michael Hampton Dec 21 '13 at 8:59

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1 Answer 1

can it be that the path MTU discovery does not work as it should? is it possible that there's some broken layer 2 device on the way?

maybe you can check if you have similar problems when connecting with badurl.com from other network locations.

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2  
More specifically - make sure that ICMP isn't blocked. It breaks IPv6, and lots of clueless admins block ICMP because they don't know what it's used for. –  pauska Dec 20 '13 at 17:38
    
badurl.com IS 100% OK from other Ipv6 networks!! And it's not just badurl.com, any IPv6 enabled website! –  gasko peter Dec 20 '13 at 18:58
    
How to find out ICMP blocked or not? Is "traceroute -I" enough? –  gasko peter Dec 20 '13 at 19:00

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