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I have a RHEL 6.3 server that has IPv6 disabled. If I enter ifconfig I get the following:

eth0      Link encap:Ethernet  HWaddr 00:50:56:9F:0F:61  
          inet addr:  Bcast:  Mask:
          RX packets:1708252 errors:0 dropped:0 overruns:0 frame:0
          TX packets:27566 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:409249072 (390.2 MiB)  TX bytes:4583283 (4.3 MiB)

My problem is that this lack of IPv6 caused our product to fail and I want to be able to reproduce this situation for a test case (so we don't fail this way in the future). Unfortunately, I have no idea how IPv6 was disabled.

One way I know that disables IPv6 is to set NETWORKING_IPV6 and IPV6INIT to false in the /etc/sysconfig/network file. This has not been done:

[root@foo bin]# cat /etc/sysconfig/network

The other way I know is to disable the ipv6 module. However, this also has not been done:

[root@foo bin]# lsmod | grep ipv6
ipv6                  322541  0 

I would like to reproduce this situation as closely as possible but I have no idea what has been done to this server to disable IPv6. Does anyone have any ideas?

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Have you tried to contact Red Hat Support, or looked in the knowledge base? – Red Tux Jan 17 '13 at 16:41
up vote 3 down vote accepted

My first guess would be some /etc/sysctl* settings, some script changing /proc/sys/net/ipv6/* or something like that in /etc/rc.local but it's hard to give an anwer as there are so many places where it could be done.

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I mentioned the /etc/sysctl setting to the person that setup the server and that rang a bell. They found a bunch of sysctl settings they had modified but had since forgotten about. – Pace Jan 18 '13 at 19:46
Some combination of net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1 presumably. – Steve-o Feb 1 '13 at 14:56

There is a good answer, but I'll add my other scenario just in case: There is a bug in older versions of ifconfig which makes it stop showing ipv6 addresses when you have complex interface names. Use

ip -6 addr ls

to be sure of assigned IPv6 addresses.

share|improve this answer
Thanks, this is good to know. – Pace Jan 22 '13 at 13:33

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