IPv6 DNS Advertisements

Feb 20

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DNS client configuration can be handled by the standard Router Advertisement Daemon (radvd) – apt-get install radvd

Edit /etc/radvd.conf on your Linux Router and insert the following at the end of the file to use Google’s DNS Caching server:

RDNS 2001:4860:4860::8888
{
};

On your Linux clients install rdnssd. To automatically add the advertised IPv6 DNS servers to your /etc/resolv.conf

The /etc/resolv.conf now contains both IPv4 and IPv6 entries. Typically a DHCP client is adding the IPv4 DNS server entries, this can be prevented by removing ‘domain-name-servers’ from the ‘request’ line in dhclient.conf

Multiple IPv6 Addresses per Interface

Mar 15

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Using ‘ifconfig’ on Debian Lenny, multiple IPv6 addresses can be added using entries in ‘/etc/network/interfaces’ with the ‘up’ and ‘down’ options. For example: 

iface eth0 inet6 static
        address 2001:41c8:1:5568::100
        netmask 64
        gateway fe80::1
        pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/autoconf
        up /sbin/ifconfig eth0 inet6 add 2001:41c8:1:5568::1:100/64
        up /sbin/ifconfig eth0 inet6 add 2001:41c8:1:5568::2:100/64
        down /sbin/ifconfig eth0 inet6 del 2001:41c8:1:5568::1:100/64
        down /sbin/ifconfig eth0 inet6 del 2001:41c8:1:5568::2:100/64

IPv6 and IPv4 Preference

Feb 27

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When a site is reachable using both IPv4 and IPv6, Linux by default has a preference which is roughly:

  1. Native IPv6
  2. Native IPv4
  3. 6to4 tunnels

To change this preference, edit ‘/etc/gai.conf’
uncomment most of the labels:

label ::1/128       0
label ::/0          1
#label 2002::/16     2
label ::ffff:0:0/96 2
label fec0::/10     3
label fc00::/7      4
label 2001:0::/32   5
label ::/96         6

(note that 2002::/16 [6to4] is left commented out)

and have the precendence configured as:

precedence  ::1/128       50
precedence  ::/0          40
precedence  2002::/16     30
precedence ::/96          20
precedence ::ffff:0:0/96  10
#
#    For sites which prefer IPv4 connections change the last line to
#
#precedence ::ffff:0:0/96  100

For these changes to have effect, restart the appropriate applications eg. Firefox.

IPv6 over IPv4 on Linux using 6to4

Feb 13

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6to4 is a tunneling protocol for using IPv6 over an IPv4 connection, and it’s configuration on Linux is well described.

Note: this can only apply to interfaces which have a public IPv4 address

A 6to4 tunnel can be configured using the following shell script

#/bin/bash

# set the interface name
if=wlan0

# calculate the IPv6 address
ipv4=`/sbin/ifconfig $if | grep "inet addr" | sed -e 's/^. *inet addr://' | sed
-e 's/ .*$//'`
ipv4s=`echo $ipv4 | tr "." " "`

ipv6=`printf "2002:%02x%02x:%02x%02x::1" $ipv4s `

case "$1" in
  start)
/sbin/ip tunnel add tun6to4 mode sit ttl 128 remote any local $ipv4
/sbin/ip link set dev tun6to4 up
/sbin/ip -6 addr add $ipv6/16 dev tun6to4
/sbin/ip -6 route add 2000::/3 via ::192.88.99.1 dev tun6to4 metric 1
# configure firewall
/sbin/ip6tables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/ip6tables -A INPUT -j DROP
    ;;
  stop)
/sbin/ip -6 route flush dev tun6to4
/sbin/ip link set dev tun6to4 down
/sbin/ip tunnel del tun6to4
# clear firewall
/sbin/ip6tables -F INPUT
  ;;
  *)
    echo "usage: ipv6 {start|stop}"
    exit 1
esac

exit 0

This will create a new interface ‘tun6to4′ which will be used for IPv6.

See here for link preference.