# IPv6

Related articles

- IPv6 - Tunnel Broker Setup

In Arch Linux, IPv6 is enabled by default. If you are looking for information regarding IPv6 tunnels, you may want to look at IPv6 - Tunnel Broker Setup.

## Privacy extensions

To enable Privacy Extensions for Stateless Address Autoconfiguration in IPv6 according to RFC 4941, reproduce the following steps:

Add these lines to `/etc/sysctl.d/40-ipv6.conf`:

    # Enable IPv6 Privacy Extensions
    net.ipv6.conf.all.use_tempaddr = 2
    net.ipv6.conf.default.use_tempaddr = 2
    net.ipv6.conf.nic0.use_tempaddr = 2
    ...
    net.ipv6.conf.nicN.use_tempaddr = 2

Where nic0 to nicN are your Network Interface Cards (the "all" or "default" parameters do not apply to nic's that already exist when the sysctl settings are applied).

After a reboot, at the latest, Privacy Extensions should be enabled.

### NetworkManager

NetworkManager does not honour the settings placed in `/etc/sysctl.d/40-ipv6.conf`. This can be verified by running `$ ip -6 addr show [device]` after rebooting: no `scope global temporary` address appears besides the regular one.

See NetworkManager#Enable_IPv6_Privacy_Extensions for a workaround.

Note: Although it may seem the `scope global temporary` IPv6 address created by enabling Privacy Extensions never gets renewed (it never shifts to `deprecated` status at the term of its `valid_lft` lifetime), it is to be verified over a longer period of time that this address does indeed change.

## Neighbor discovery

Pinging the multicast address `ff02::1` results in all hosts in link-local scope responding. An interface has to be specified. With a ping to the multicast address `ff02::2` only routers will respond.

    $ ping6 ff02::1%eth0

If you add an option `-I your-global-ipv6`, link-local hosts will respond with their link-global scope addresses. The interface can be omitted in this case.

    $ ping6 -I 2001:4f8:fff6::21 ff02::1

## Static address

Sometime using static address can improve security. For example, if your local router uses Neighbor Discovery or radvd (RFC 2461), your interface will automatically be assigned an address based its MAC address (using IPv6's Stateless Autoconfiguration). This may be less than ideal for security since it allows a system to be tracked even if the network portion of the IP address changes.

To assign a static IP address using netctl, look at the example profile in `/etc/netctl/examples/ethernet-static`. The following lines are important:

    /etc/netctl/examples/ethernet-static

    ...
    # For IPv6 static address configuration
    IP6=static
    Address6=('1234:5678:9abc:def::1/64' '1234:3456::123/96')
    Routes6=('abcd::1234')
    Gateway6='1234:0:123::abcd'

## IPv6 on Comcast

`dhcpcd -4` or `dhcpcd -6` worked using a Motorola SURFBoard 6141 and a Realtek RTL8168d/8111d. Either would work, but would not run dual stack: both protocols and addresses on one interface. (The `-6` command would not work if `-4` ran first, even after resetting the interface. And when it did, it gave the NIC a /128 address.) Try these commands:

    dhclient -4 enp3s0
    dhclient -P -v enp3s0

The `-P` argument grabs a lease of the IPv6 prefix only. `-v` writes to `stdout` what is also written to `/var/lib/dhclient/dhclient6.leases`:

    Bound to *:546
    Listening on Socket/enp3s0
    Sending on   Socket/enp3s0
    PRC: Confirming active lease (INIT-REBOOT).
    XMT: Forming Rebind, 0 ms elapsed.
    XMT:  X-- IA_PD a1:b2:cd:e2
    XMT:  | X-- Requested renew  +3600
    XMT:  | X-- Requested rebind +5400
    XMT:  | | X-- IAPREFIX 1234:5:6700:890::/64

IAPREFIX is the necessary value. Substitute `::1` before the CIDR slash to make the prefix a real address:

    ip -6 addr add 1234:5:6700:890::1/64  dev enp3s0

## Disable IPv6

Note: The Arch kernel has IPv6 support built in directly [1], therefore a module cannot be blacklisted.

### Disable functionality

Adding `ipv6.disable=1` to the kernel line disables the whole IPv6 stack, which is likely what you want if you are experiencing issues. See Kernel parameters for more information.

Alternatively, adding `ipv6.disable_ipv6=1` instead will keep the IPv6 stack functional but will not assign IPv6 addresses to any of your network devices.

One can also avoid assigning IPv6 addresses to specific network interfaces by adding the following sysctl config to `/etc/sysctl.d/40-ipv6.conf`:

    # Disable IPv6
    net.ipv6.conf.all.disable_ipv6 = 1
    net.ipv6.conf.interface0.disable_ipv6 = 1
    ...
    net.ipv6.conf.interfaceN.disable_ipv6 = 1

Note that you must list all of the targeted interfaces explicitly, as disabling "all" does not apply to interfaces that are already "up" when sysctl settings are applied.

Note 2, if disabling IPv6 by sysctl, you should comment out the IPv6 hosts in your `/etc/hosts`-file.

    #<ip-address>	<hostname.domain.org>	<hostname>
    127.0.0.1	localhost.localdomain	localhost
    #::1		localhost.localdomain	localhost

otherwise there could be some connection errors because hosts are resolved to their IPv6 address which is not reachable.

### Other programs

Disabling IPv6 functionality in the kernel does not prevent other programs from trying to use IPv6. In most cases, this is completely harmless, but if you find yourself having issues with that program, you should consult the program's manual pages for a way to disable that functionality.

For example, dhcpcd will continue to harmlessly attempt to perform IPv6 router solicitation. To disable this, as stated in the dhcpcd.conf man page, add the following to `/etc/dhcpcd.conf`:

    noipv6rs

## See also

- IPv6 - kernel.org Documentation
- IPv6 temporary addresses and privacy extensions

Category:

- Networking