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I'm trying to disable IPv6 completely on my NFS server (Ubuntu 12.04 LTS precise), but still seem to have some IPv6 ports listening as shown when I run netstat -lp:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 *:60377                 *:*                     LISTEN      -               
tcp        0      0 *:49115                 *:*                     LISTEN      1744/rpc.mountd 
tcp        0      0 *:nfs                   *:*                     LISTEN      -               
tcp        0      0 *:54658                 *:*                     LISTEN      1744/rpc.mountd 
tcp        0      0 *:sunrpc                *:*                     LISTEN      450/rpcbind     
tcp        0      0 *:55730                 *:*                     LISTEN      709/rpc.statd   
tcp        0      0 *:48181                 *:*                     LISTEN      1744/rpc.mountd  
tcp6       0      0 [::]:37004              [::]:*                  LISTEN      -               
udp        0      0 *:55738                 *:*                                 1744/rpc.mountd 
udp        0      0 *:43533                 *:*                                 -               
udp        0      0 *:43687                 *:*                                 709/rpc.statd   
udp        0      0 *:sunrpc                *:*                                 450/rpcbind          
udp        0      0 *:615                   *:*                                 450/rpcbind     
udp        0      0 localhost:885           *:*                                 709/rpc.statd   
udp        0      0 *:50206                 *:*                                 1744/rpc.mountd 
udp        0      0 *:54380                 *:*                                 1744/rpc.mountd 
udp        0      0 *:nfs                   *:*                                 -               
udp6       0      0 [::]:46857              [::]:*                              -               

I have disabled IPv6 on a kernel level in /etc/sysctl.d/ipvf-disable.conf:

#disable ipv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

And also in /etc/netconfig:

udp        tpi_clts      v     inet     udp     -       -
tcp        tpi_cots_ord  v     inet     tcp     -       -
#udp6       tpi_clts      v     inet6    udp     -       -
#tcp6       tpi_cots_ord  v     inet6    tcp     -       -
rawip      tpi_raw       -     inet      -      -       -
local      tpi_cots_ord  -     loopback  -      -       -
unix       tpi_cots_ord  -     loopback  -      -       -

After these changes were made, I rebooted and the above netstat output didn't change. The UDP6 and TCP6 ports that are open seem to be kernel ports (hence the lack of PID), and they disappear when I run /etc/init.d/nfs-kernel-server stop.

I found the following bug report: that matches my issue, but it doesn't seem to have any replies. Am I missing something here, or is this a bug?

EDIT - To clarify, there is code that does not run well with any IPv6 (yes, it's crappy code and it can't be changed easily) as it reads netstat and breaks. Any ideas on how to remove the IPv6 references from netstat would be appreciated.

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Disabling IPv6 is a very bad idea. Whatever the real problem is that you're trying to solve, this is just going to cause you more problems in the future. – Michael Hampton Mar 9 '14 at 23:40
Just wondering: Why do you want to turn off IPv6 so badly? And why is it a problem that the kernel NFS server is bound to an IPv6-capable socket when you don't have any IPv6 addresses on your host? You won't get any incoming IPv6 traffic without having IPv6 addresses anyway. – Sander Steffann Mar 9 '14 at 23:40
I'm disabling IPv6 because the code running on the server cannot run with it. It reads the netstat output and fails when it encounters ipv6. The developers who wrote the code are no longer available to update it, so i'm hoping to resolve it from an OS point of view. It was working before because it was running on an old OS. It needs to be moved. – serafinius Mar 10 '14 at 0:20
Why don't you just add a -4 to the netstat command that the program calls? It will then only show IPv4 information. – Michael Hampton Mar 10 '14 at 3:38
@MichaelHampton thanks for your replies. I would change the code if I could, but I didn't write the app and don't have the skills to reverse engineer the code. – serafinius Mar 10 '14 at 3:54

For the sake of being complete, I managed to get get a workaround for this specific case going by creating a "netstat" shell script that parses IPv6 out of the existing netstat and feeding the application an alternative PATH including this script.

NOTE - This is obviously not a good idea as a permanent fix, but with no better option open to me it seemed to work.

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