Automatic IPv6 due to broadcast

Matthew Huff mhuff at
Mon Apr 16 13:24:51 CDT 2012

To completely disable ipv6 in Redhat:

1) Modify /etc/modprobe.conf (add)    
  alias ipv6 off
  alias net-pf-10 off
  options ipv6 disable=1

2) Modify /etc/sysconfig/network (add)


   I usually also add


That should completely disable ipv6 in Redhat 5.x

Matthew Huff             | 1 Manhattanville Rd
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039
aim: matthewbhuff        | Fax:   914-460-4139

> -----Original Message-----
> From: Anurag Bhatia [mailto:me at]
> Sent: Monday, April 16, 2012 2:10 PM
> To: NANOG Mailing List
> Subject: Automatic IPv6 due to broadcast
> Hello everyone
> Just got a awfully crazy issue. I heard from our support team about
> failure of whois during domain registration. Initially I thought of
> port 43 TCP block or something but found it was all ok. Later when ran
> whois manually on server via terminal it failed. Found problem that
> server was connecting to whois server - I was
> stunned! Server got IPv6 and not just that one - almost all. This was
> scary - partial IPv6 setup and it was breaking things.
> In routing tables, routes were all going to a router which I recently
> setup for testing. That router and other servers are under same switch
> but by no means I ever configured that router as default gateway for
> IPv6. I found option of "broadcast" was enabled on router for local
> fe80... address and I guess router broadcasted IPv6 and somehow (??)
> all servers found that they have a IPv6 router on LAN and started using
> it - automated DHCP IPv6?
> I wonder if anyone else also had similar issues? Also, if my guesses
> are correct then how can we disable Red Hat distro oriented servers
> from taking such automated configuration - simple DHCP in IPv6 disable?
> Thanks
> --
> Anurag Bhatia
> or simply - http://[2001:470:26:78f::5] if you are on IPv6 connected
> network!
> Twitter: @anurag_bhatia <!/anurag_bhatia>
> Linkedin:
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