[CentOS] How to disable ipv6

Wed Nov 28 20:11:58 UTC 2012
Charles Bearden <Charles.F.Bearden at uth.tmc.edu>

On 11/28/2012 12:45 PM, Johnny Hughes wrote:
> On 11/28/2012 12:25 PM, Charles Bearden wrote:
>> Hi all,
>> I'm pretty new to CentOS. I am working with a newly set-up server:
>> [cbearden at host ~]$ lsb_release -a
>> LSB Version:
>> :core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
>> Distributor ID:	CentOS
>> Description:	CentOS release 6.3 (Final)
>> Release:	6.3
>> Codename:	Final
>> I'm trying to solve this problem (X11 forwarding)
>>     http://thread.gmane.org/gmane.linux.centos.general/119342/focus=119347
>> for myself.
>> But disabling ipv6 and adding
>>     AddressFamily inet
>> to my sshd config didn't fix the problem. Oddly enough, the output of
>>     netstat -an
>> suggests that ipv6 is still enabled:
>>     tcp        0      0 :::22                       :::*                   LISTEN
>> even though
>>     [cbearden at PostgreSQL ~]$ cat /proc/sys/net/ipv6/conf/all/disable_ipv6
>>     1
>> This is after a reboot. Am I right that the /proc file suggests that ipv6 is
>> disabled while netstat suggests that it isn't?
>> Thanks,
>> Chuck
> http://wiki.centos.org/FAQ/CentOS6#head-d47139912868bcb9d754441ecb6a8a10d41781df

Thanks to Mark, Barry, and Johnny for their swift responses.

I tried the steps at the wiki page above, but no joy. In particular, when I 
restart sshd, it appears that the 'stop' part fails:

# /etc/init.d/sshd restart
Stopping sshd:                                             [FAILED]
Starting sshd:                                             [  OK  ]

Despite altering both values via sysctl and adding the AddressFamily line and 
uncommenting ListenAddress, sshd appears still to be listening on :::22. 
Other processes are still listening on ipv6-bound ports as well.

Do I need to explicitly remove the ipv6 kernel module? I probably can't while 
some daemons are bound to ::: ports. Sorry if I'm being dense here.

I don't know if this makes any difference, but the CentOS system is running in a 
VM. It's not a setup I chose or ultimately control.

Chuck Bearden
Programmer Analyst IV
The University of Texas Health Science Center at Houston
School of Biomedical Informatics
Email: Charles.F.Bearden at uth.tmc.edu
Phone: 713.500.9672