Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

How come a:

curl -v -6

doesn't work but a:

curl -v -6 --head

Perfectly works?

MTU isn't the problem (?) since:

root@server:~# ping6 -c 10 -s 2000 -M do 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?

share|improve this question

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

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions must be relevant to professional system administration. Server Fault is dedicated to professional system and network administrators. End user and enthusiast questions are off-topic (contact your system administrator or hire a professional to help you out). Please see the Help Center for more information." – Michael Hampton
If this question can be reworded to fit the rules in the help center, please edit the question.

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 from other network locations.

share|improve this answer
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 IS 100% OK from other Ipv6 networks!! And it's not just, 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

Not the answer you're looking for? Browse other questions tagged or ask your own question.