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Is there any information on configuring IPv6 on an Debian 9 VPS running on OpenVZ? I have a VPS which was running an older version of Debian on OpenVZ which I needed to upgrade to support some newer software. After the upgrade my IPv6 interface configuration does not seem to be working. IPv6 was working just fine before upgrading Debian on the same VPS.

The auto-generated /etc/network/interfaces (which was working before) is:

auto venet0
iface venet0 inet manual
        up ifconfig venet0 up
        up ifconfig venet0 127.0.0.2
        up route add default dev venet0
        down route del default dev venet0
        down ifconfig venet0 down


iface venet0 inet6 manual
        up ifconfig venet0 add 2604:880:26::a4cd:e7e/128
        down ifconfig venet0 del 2604:880:26::a4cd:e7e/128
        up route -A inet6 add default dev venet0
        down route -A inet6 del default dev venet0

auto venet0:0
iface venet0:0 inet static
        address 172.93.54.230
        netmask 255.255.255.255

So it appears I should also be able to configure IPv6 from the command line with ifconfig or ip address add commands but when I do I receive "no buffer space available messages (see below):

root@dal1:/# ifconfig venet0 add 2604:880:26::a4cd:e7e/128
SIOCSIFADDR: No buffer space available
root@dal1:/# ip address add 2604:880:26::a4cd:e7e/128 dev venet0
RTNETLINK answers: No buffer space available
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  • Why are you using up/down commands instead of the normal address netmask and gateway? – Michael Hampton Jan 4 '18 at 22:20
  • Unsure. The original OpenVZ template which the VPS provider deployed the machine with had it that way. Not being an OpenVZ expert I assumed that it was something related to the OpenVZ environment. – Ben Franske Jan 5 '18 at 0:16
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It may be a MTU related problem.

Try adding mtu 1500 or some other sensible values in your add operation. If this solves the problem, the correct value to use will depend on your provider, so ask him what to use.

A change of version may have changed the default value of the MTU if not provided, and based in some reports it seems to be sometimes 0 as default, so that can not work.

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  • I saw some references to the MTU issue in my googling as well. In checking it though it was already set to 1500. I tried resetting it to 1500 and applying an IP address again but still had the same problem. – Ben Franske Jan 6 '18 at 2:45

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