How to disable autoconfiguration on IPv6 in Linux?

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

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.

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.