23

How can I permanently disable autoconfiguration of IPv6 in Linux? When I try to manually delete an address from an interface with:

ip -6 addr del 2001:0db8:85a3:0000:0000:8a2e:0370:7334/64 dev eth1

It will reappear a few seconds later, I want it to be gone permanently, but without disabling IPv6 all together.

22

Auto configuration can be disabled temporary for eth1 with:

sudo sysctl -w net.ipv6.conf.eth1.autoconf=0
sudo sysctl -w net.ipv6.conf.eth1.accept_ra=0

or for all interfaces with:

sudo sysctl -w net.ipv6.conf.all.autoconf=0
sudo sysctl -w net.ipv6.conf.all.accept_ra=0

Reenabling works by using 1 instead of 0 in the call.

Disabling it permanently can be done with an entry to /etc/sysctl.conf. On Debian Etch (probably on newer too), without setting the accept_ra, the system will autoconfigure using the Link local adress (fe80..)

As Gart mentioned below, automatic address configuration and router discovery will be disabled if the host itself is a router and accept_ra is not 2, i.e

net.ipv6.conf.<iface|all|default>.forwarding=1

and

net.ipv6.conf.<iface|all|default>.accept_ra=0 or net.ipv6.conf.<iface|all|default>.accept_ra=1.

where iface is your interface

|improve this answer|||||
  • 4
    Also, automatic address configuration and router discovery will be disabled if the host itself is a router, i.e net.ipv6.conf.all.forwarding=1 is set. – Gart Sep 18 '11 at 13:25
5

The sysctl solution did not work for us on Ubuntu 18.04 Bionic. We solved it by:

Editing /etc/netplan/01-netcfg.yaml, configure:

network:
  ...
  ethernets:
    eth0:
      ...
      dhcp6: no
      accept-ra: no

You may need to use your interface name instead of eth0. After you save the file execute:

netplan apply or reboot

If you already have received an IPv6 IP from autoconfiguration and you want to remove it without rebooting, you can execute:

ip -6 addr del 1111:2222:1:0:aaaa:bbbb:cccc:dddd/64 dev eth0 

Of course you need to replace the IP and device in this command.

|improve this answer|||||
  • this has just made my day been scratching my head on this for a few months :D – anthonysomerset Sep 19 '18 at 12:48
  • 2
    I usually just scratch Google till I find it. – Jeroen Vermeulen - MageHost Sep 19 '18 at 13:09
  • 1
    This worked when I tried it, but the problem is turning accept-ra off is quite dangerous, as mentioned by Mark S - it appears to work but later you may find you're missing packets because they hit a fragmentation point or a failover router is used. Also it breaks pings. The reason I was trying to do this was to reliably match my SPF record in outgoing mail but then I realised I should have been using a netmask in the record instead because in IPv6 a range of addresses effectively belongs to a machine, not a single address. – Phil McKerracher Oct 26 '18 at 4:08
4

net.ipv6.conf.all.accept_ra=0 above should not be done, as RAs are necessary for indication of on-link and off-link for the prefix (as per RFC5942), as well as automated configuration of a number of other parameters, such as MTU, Neighbor Discovery timeouts etc.

If you want to disable autoconfiguration, either set the autoconf sysctl off as above, or switch off the A (autoconfiguration bit) in the Prefix Information Option (PIO) in the RA.

|improve this answer|||||
3
sudo sysctl -w net.ipv6.conf.all.autoconf=0

This didn't work for me on Debian Wheezy. After examining /etc/sysctl.conf I needed to use

sudo sysctl -w net.ipv6.conf.default.autoconf=0
|improve this answer|||||
2

The problem with Ubuntu 18 and ipv6 is that systemd-networkd controls kernel parameters, so though one might disable ipv6 with sysctl, networkd will be more than happy switching them on for you, if the configuration does not state otherwise.

My solution to disable ipv6 is to configure link-local in netplan to an empty scalar (provided you have no link-local ipv4 IPs)

network:
     version: 2
     renderer: networkd
     ethernets:
     eth0:
        ..
        link-local: [ ]

The configuration will compile configuration for networkd that will be posted in /run/systemd/network/10-netplan-eth0.network and that will convince networkd not to put up ipv6 for eth0

If you may want to disable ipv6 also on the loopback, it is easily achieved by setting the kernel parameter net.ipv6.conf.all.disable_ipv6 to 1. networkd does not seem to control loopback.

sysctl -w net.ipv6.conf.all.disable_ipv6=1
|improve this answer|||||
  • I really like your very clean solution. As we don't use link-local addresses adding the empty scalar the perfect solution. After this, we had to reboot the server as netplan apply kept the already assigned IPv6 addresses on both of our ethernet interfaces. But after reboot, everything works just like you said. I don't think there is a reason to bother with disabling IPv6 on the loopback interface, so I just skipped the sysctl part. Thanks! – Zoltan May 6 '19 at 15:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for?Browse other questions tagged or ask your own question.