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Bug 161012 - IPv6 enabled on default, hangs when sending DNS requests
Summary: IPv6 enabled on default, hangs when sending DNS requests
Alias: None
Product: Fedora
Classification: Fedora
Component: bind
Version: 4
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Jason Vas Dias
QA Contact:
Depends On:
TreeView+ depends on / blocked
Reported: 2005-06-19 20:16 UTC by Amrinder Brar
Modified: 2007-11-30 22:11 UTC (History)
0 users

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2005-07-12 18:38:31 UTC

Attachments (Terms of Use)

Description Amrinder Brar 2005-06-19 20:16:04 UTC
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050524 Fedora/1.0.4-4 Firefox/1.0.4

Description of problem:
IPv6 is enabled by default in FC4, and a lot of old routers do not support it.  As a result, DNS Lookups take forever, because each time a DNS request is made, it takes a while to figure out that it has to fall back on IPv4.  More importantly, there is no easy way within the GUI to disable IPv6.  Ofcourse, a method in doing this would be editing /etc/modprobe.conf and adding "alias net-pf-10 off".  I believe this is a signficant bug, because many newbies who aren't familiar with linux will not know how to fix this problem, and got back to Windows...

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
use a router that doesn't support IPv6

Actual Results:  Browser hangs while looking up DNS, takes time to fall back on IPv4

Expected Results:  There shoudl be an option to disable IPv6 withing GUI, or perhaps something to detect if IPv6 is not supported.

Additional info:

Comment 1 Jason Vas Dias 2005-07-05 19:14:15 UTC
Sorry for the delay in processing this bug - I just got back from

This has nothing to do with the DHCPv6 package, which is for obtaining
IPv6 addresses and router subnet delegations with DHCP - if you had
been using it, IPv6 must have been enabled on your network; if you
are using it and your network has no IPv6 router, you are asking for
this type of problem - if this is the case, disable dhcpv6 and the
problem should go away - if not, read on.

You do not need to disable IPv6 - by default, the glibc resolver
should be asking for IPv4 addresses before IPv6 addresses.

So it appears you may have a problem with the glibc resolver,
or with your nameservers.

Please supply some further information :
1. Do you have an "options inet6" statement in /etc/resolv.conf ?
   If so, remove it - this makes the glibc resolver always query
   for AAAA addresses first.
   If not, the problem is likely to be with your nameservers.

2. Do you know what version of BIND your nameservers use? 
   Old nameservers (prior to 9.3.0 / 9.2.5) have a problem with 
   timing out when root nameservers provide their IPv6 addresses
   before their IPv4 addresses ( bug 140528 ) when not connected
   to the IPv6 backbone. If you can, get your nameserver operators
   to upgrade their nameservers.

3. If neither (1) nor (2) apply, please collect this information:
   As root, run the command:
   # tcpdump -nl -vvv -s 2048 port domain 2>&1 | tee /tmp/tcpdump.log&
   Then reproduce the timeout problem with your browser. Once you 
   have reproduced it, then :
   # pkill tcpdump
   and append the /tmp/tcpdump.log file to this bug report.

You may also workaround the problem by installing the latest bind-*
and caching-nameserver packages, and doing:
   # chkconfig --level=2345 named on; chkconfig --level=016 named off;
   # echo 'supersede domain-name-servers;' \ 
   # service named start
   # ifdown eth0; ifup eth0
You'll then be using bind as a caching only nameserver, which will
attempt to contact the root nameservers directly and which does not
have the IPv6 timeout problem . NOTE: to do this, any firewalls must
allow your machine UDP port 53 access to the external internet.

I hope the above helps - if not, please let me know - thank you!

Comment 2 Jason Vas Dias 2005-07-12 18:38:31 UTC
I cannot reproduce this problem, and the further information requested was not
forthcoming. If it is still an issue for you, please supply the requested 
information and re-open this bug - closing it out as non-reproducible for now.

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