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I have this configuration Ubuntu 18.04:

sudo nano /etc/sysctl.d/99-sysctl.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
sudo sysctl -p
cat /proc/sys/net/ipv6/conf/all/disable_ipv6
1

And my /etc/netplan/*.yaml

dhcp6: no

But I still have IPv6 traffic, as seen in this netdata report:

Netdata Report

Why? How can I completely block IPv6?

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6
  • 1
    Why not? Just because you select to ignore doesn’t mean you don’t receive it.
    – Daniel B
    May 31, 2018 at 17:19
  • ok, but how I block it completely?
    – acgbox
    May 31, 2018 at 17:23
  • 1
    You can’t, not on the device itself. Some external firewall would have to. But why even bother? It’s not like the traffic does anything. Perhaps you should explain your motivation.
    – Daniel B
    May 31, 2018 at 17:32
  • 2
    I don't think that's using much in terms of resources. And by much I mean anything measurable.
    – Dessa Simpson
    May 31, 2018 at 19:53
  • 1
    It's 2018. You should be supporting both IPv4 and IPv6, equally, otherwise you could be scrambling to implement IPv6 at some point when you are not prepared for it and don't understand it enough to do it correctly.
    – Ron Maupin
    May 31, 2018 at 21:20

1 Answer 1

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That Netdata report showed that IPv6 traffic was only received by your host, not sent. But I doubt it was actively received by an IPv6 stack. What you are seeing is probably just some broadcast packets on your LAN that used EtherType 0x86DD (IPv6), and your NIC dutifully passed those up to your host OS as NICs are supposed to do. NICs are only supposed to know their own layer, which is Layer 2, the Data Link layer where Ethernet lives, not layer 3, the Network layer where IP[v4|v6] lives). So a NIC shouldn't treat EtherType 0x86DD specially, it should just blindly pass those frames up to the host OS's network stack and let the host OS's network stack decide to deal with them or drop them. You had probably successfully disabled all IPv6 support in Ubuntu, so there was nothing listening for EtherType 0x86DD, so those frames were probably discarded by the lowest layers of the Ubuntu network stack the moment the NIC passed them up to Ubuntu.

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