Contents

Preface
Install necessary software
Setup software
1. Kernel
2. IPTables
Setup IPv6 connectivity
IPv6 on the LAN
Example for debugging purposes
Using IPv6 by default with Windows XP
Using IPv6 by default with Windows Vista
Links
ToDo
Questions

1. Preface

This HOWTO describes how to setup IPv6 on your OpenWrt-based router.

There are two big, different steps :

Setup a working ipv6 connection on the OpenWRT router. This can either be:
- using a tunnel broker (like SixXS, hurricane electric, or the services provided by a tunnel broker that supports the Tunnel Setup Protocol (TSP), such as the Hexago Gateway6).
- using 6to4, a standard encapsulation protocol for IPv6 over IPv4
Propagate the IPv6 subnet to the LAN with radvd

2. Install necessary software

To use IPv6, we need the following modules:

IPv6 kernel module (always)
IPv6 routing software (always, to configure IPv6 routing)
ip6tables kernel modules (optional, if you need an IPv6 firewall)
ip6tables command-line tool (optional, to configure the IPv6 firewall)

2.1. Install the IPv6 kernel modules

ipkg install kmod-ipv6

2.2. Install the routing software

To configure the interfaces and the routing tables we need the new iputils. Additionally we need the route advertising daemon to propagate the IPv6 route to our local subnet.

ipkg install radvd
ipkg install ip

2.3. Install the ip6tables kernel modules

ipkg install kmod-ip6tables

2.4. Install the ip6tables package

ipkg install ip6tables

3. Setup software

3.1. Kernel

The ipv6 module is automatically loaded at boot time via /etc/modules.d/20-ipv6, if you don't want to reboot issue

insmod ipv6

to load the ipv6 module into the kernel.

After this your router has IPv6 support. To check this you could use ifconfig to validate the ::1/128 IPv6 address is assigned to the loopback device.

# ifconfig lo
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:116 errors:0 dropped:0 overruns:0 frame:0
          TX packets:116 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:10395 (10.1 KiB)  TX bytes:10395 (10.1 KiB)

Optionally, you can load the ip6table modules into the kernel by issuing the following:

insmod ip6_tables
insmod ip6table_filter

To load ip6tables at boot, add the following to /etc/modules.d/20-ipv6 or /etc/modules

ip6_tables
ip6table_filter

To check the installation of ip6tables you can use the ip6tables show command.

# ip6tables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

3.2. IPTables

In my firewall script I had to add the following rule to let the encapsulated packets pass:

iptables -A INPUT -p 41 -i $WAN -j ACCEPT

Or, if you have /etc/config/firewall, you can add this line there instead of the above:

accept:proto=41

If your Openwrt is also a NAT you should add the following to prevent protocol 41 (6in4) to get listed on the NAT table. Otherwise your tunnel goes down after some time. (See https://noc.sixxs.net/faq/connectivity/?faq=conntracking.)

iptables -t nat -D POSTROUTING -o $WAN -j MASQUERADE
iptables -t nat -A POSTROUTING --protocol ! 41 -o $WAN -j MASQUERADE

You need to place it into the right position of your firewall script (eg: just after/before "iptables -A INPUT -p 47 -j ACCEPT" ).

Note: in recent versions of WhiteRussian the firewall script should go in /etc/firewall.user and INPUT changed to input_rule, POSTROUTING changed to postrouting_rule. This ensures that the lines are added to the tables in the correct order.

4. Setup IPv6 connectivity

You can choose between using 6to4 (standard, works from anywhere) or a SixXS tunnel (if you are near a Point of Presence). 6to4 is probably the quickest to setup at first.

Using the Hexago OpenWRT Gateway6 Client, it is also possible to establish a tunnel to a tunnel broker that supports the TSP protocol.

4.1. 6to4 with a direct connection to the Internet

This applies e.g. if you WAN port (on vlan1) receives an public IPv4 address through DHCP or is assigned a static public IPv4 address.

Update: If running version 0.9, you probably should be following the same documentation as the PPP case below. Those same scripts as PPP are called when starting and stopping the wan in that version.

To have the 6to4 tunnel start up automatically on boot, copy this script in /etc/init.d/tun6to4:

#!/bin/sh /etc/rc.common
# 6to4 tunnel
# retrieve the public IPv4 address
ipv4=`ip -4 addr | awk '/^[0-9]+[:] vlan1[:]/ {l=NR+1} /inet (([0-9]{1,3}\.){3}[0-9]{1,3})\// {if (NR == l) split($2,a,"/")} END {print a[1]}'`
# (you may also write e.g. "ipv4=82.54.194.11" if your IP address does not change)
# get the IPv6 prefix from the IPv4 address
ipv6prefix=`echo $ipv4 | awk -F. '{ printf "2002:%02x%02x:%02x%02x", $1, $2, $3, $4 }'`
# the local subnet (any 4 digit hex number)
ipv6subnet=1234
# The 6to4 relay: here are a few, use the anycast address when possible
# For others see http://www.kfu.com/~nsayer/6to4/#list or google
# anycast:
relay6to4=192.88.99.1
# uni-leipzig.de:
#relay6to4=139.18.25.33
# 6to4.ipv6.bt.com
#relay6to4=194.73.82.244
# microsoft
#relay6to4=131.107.33.60
# japan kddilab.6to4.jp
#relay6to4=192.26.91.178
  start() {
    echo "Creating tunnel interface..."
    ip tunnel add tun6to4 mode sit ttl 64 remote any local $ipv4
    echo "Setting tunnel interface up..."
    ip link set dev tun6to4 up
    echo "Assigning ${ipv6prefix}::1/16 address to tunnel interface..."
    ip -6 addr add ${ipv6prefix}::1/16 dev tun6to4
    echo "Adding route to IPv6 internet on tunnel interface via relay..."
    ip -6 route add 2000::/3 via ::${relay6to4} dev tun6to4 metric 1
    # the following lines do not seem to be necessary
    #ip -6 addr add ${ipv6prefix}:${ipv6subnet}::3/64 dev vlan1
    #ip -6 route del ${ipv6prefix}:${ipv6subnet}::/64 dev vlan1
    echo "Assigning ${ipv6prefix}:${ipv6subnet}::1/64 address to br0 (local lan interface)..."
    ip -6 addr add ${ipv6prefix}:${ipv6subnet}::1/64 dev br0
    echo "Done."
  }
  stop() {
    #echo "Removing WAN (external) interface IPv6 address..."
    #ip -6 addr del ${ipv6prefix}:${ipv6subnet}::3/64 dev vlan1
    echo "Removing br0 (internal lan) interface IPv6 address..."
    ip -6 addr del ${ipv6prefix}:${ipv6subnet}::1/64 dev br0
    echo "Removing routes to 6to4 tunnel interface..."
    ip -6 route flush dev tun6to4
    echo "Setting tunnel interface down..."
    ip link set dev tun6to4 down
    echo "Removing tunnel interface..."
    ip tunnel del tun6to4
    echo "Done."
  }
  restart() {
    stop
    start
}

4.2. 6to4 tunnel with an Internet connection that uses PPP

If you connect to your ISP using PPP (usually PPPoE): When the ppp interface comes up, the ppp daemon calls the /etc/ppp/ip-up script, when it goes down the /etc/ppp/ip-down script. Those scripts call /etc/hotplug.d/iface/* with the appropriate parameters.

Update: The line that sets the IPV4 address may fail on 0.9 and or certain ISPs (ex. Comcast uses some /22 routing). Try adding "| grep -v inet6" before the cut to fix the issue with getting ipv6 stuff in the result and try adding "| cut -d / -f 1" to the end to get rid of the network specification. Adding an echo $IPV4 to the script can help with debugging.

To set up ipv6 support write /etc/hotplug.d/iface/10-ipv6

. /etc/functions.sh
NAME=ipv6
COMMAND=/usr/sbin/ip
[ "$ACTION" = "ifup" -a "$INTERFACE" = "wan" ] && {
        [ -x $COMMAND ] && {
                IFNAME=$(nvram get ${INTERFACE}_ifname)
                IPV4=$(ip addr show $IFNAME | grep inet | cut -f6 -d' ')
                IPV6PREFIX=$(echo $IPV4 | awk -F. '{ printf "2002:%02x%02x:%02x%02x", $1, $2, $3, $4 }')
                ip tunnel add tun6to4 mode sit ttl 64 remote any local $IPV4
                ip link set dev tun6to4 up
                ip -6 addr add ${IPV6PREFIX}::1/16 dev tun6to4
                ip -6 route add 2000::/3 via ::192.88.99.1 dev tun6to4 metric 1
                ip -6 addr add ${IPV6PREFIX}:5678::1/64 dev br0
        } &
}
[ "$ACTION" = "ifdown" -a "$INTERFACE" = "wan" ] && {
        [ -x $COMMAND ] && {
                IFNAME=$(nvram get ${INTERFACE}_ifname)
                IPV4=$(ip addr show $IFNAME | grep inet | cut -f6 -d' ')
                IPV6PREFIX=$(echo $IPV4 | awk -F. '{ printf "2002:%02x%02x:%02x%02x", $1, $2, $3, $4 }')
                ip -6 addr del ${IPV6PREFIX}:5678::1/64 dev br0
                ip -6 route flush dev tun6to4
                ip link set dev tun6to4 down
                ip tunnel del tun6to4
        } &
}

Warning: use prefix 0:0:0:5678::/64 in your /etc/radvd.conf. The subnet 5678 is hardcoded in this script.

4.3. Native IPv6 with an Internet connection that uses PPP

Kamikaze 7.09 supports IPv6 on PPP.

Activate PPP IPv6 support. Add following lines to /etc/ppp/options :

+ipv6
#debug
#logfile /var/log/ppp.log

Uncomment the lines if you need to debug PPP.

Add your static IPv6 address to your LAN interface in /etc/config/network :

option ip6addr  xxxx:xxxx:xxxx:xxxx::1/64

Restart the network

/etc/init.d/network restart

4.4. Static tunnel to SixXS.net

Note: this script should works with any Tunnel Broker

#!/bin/sh /etc/rc.common
LOCALIP=Your IPv4 Endpoint
POPIP=POP IPv4 Endpoint
LOCTUN=Your IPv6 Endpoint
REMTUN=SixXS IPv6 Endpoint
START=50
start() {
        echo -n "Starting SixXS.Net IPv6 tunnel: "
        ip tunnel add sixxs mode sit local $LOCALIP remote $POPIP
        ip link set sixxs up
        ip link set mtu 1280 dev sixxs
        ip tunnel change sixxs ttl 64
        ip -6 addr add $LOCTUN/64 dev sixxs
        ip -6 ro add default via $REMTUN dev sixxs
        echo "Done."
}
stop() {
        echo -n "Stopping SixXS.Net IPv6 tunnel: "
        ip link set sixxs down
        ip tunnel del sixxs
        echo "Done."
}
restart() {
        stop
        start
}

Note: I had to add "ttl 64" to the "ip tunnel add sixxs" line in order to be able to do traceroutes. Without it, traceroute6's did work, but slowly and with all intermediate hops missed ("* * *"). With this setting it works. -RZ

4.5. Dynamic (heartbeat) tunnel to SixXS.net

ipkg install aiccu

Edit /etc/aiccu.conf :

put your login/passwd
configure "ipv4_interface" (usually vlan1)
comment the "tunnel_id" line if you have only one tunnel

$/!\$ From the SixXS documentation : Keep your machine NTP synced, if the timestamp difference is bigger than 120 seconds the heartbeat will be silently dropped. Note also that you need to select the correct time zone.

This can be solved by installing ntpclient (to correctly set the clock on boot) and openntpd (to manage the drift).

Now start the sixxs client :

aiccu start

If it doesn't work use logread to see what occurs

4.6. Establishing a TSP tunnel using the Hexago OpenWRT Gateway6 Client

Download the Hexago OpenWRT Gateway6 Client from the go6.net Portal.
Install the software as explained in the Hexago OpenWRT Gateway6 Client README, available from the same location.
Follow the instructions provided in the Hexago OpenWRT Gateway6 Client README to configure and establish a tunnel to a tunnel broker that supports the Tunnel Setup Protocol (TSP).

Freenet6, a service offered by the go6.net Portal and backed by the Hexago Gateway6 product, provides free IPv6 access through the TSP protocol. To obtain access to the free service, simply register on the go6.net Portal registration page.

5. IPv6 on the LAN

At this point I suppose that you have a working ipv6 connection on the wrt, that you can ping6 www.kame.net without error.

Note: When using a SixXS tunnel (and probably others), only ::1 (the PoP) and ::2 (your endpoint) can be used as the rest is not routed! Therefore, you need to request a subnet and enable it before you are able to utilize radvd.

Using our mythical 2001:db8:0:f101::/64 network, we would put in /etc/radvd.conf the following lines:

# For more examples, see the radvd documentation.
interface br0
{
        AdvSendAdvert on;
        prefix 2001:db8:0:f101::/64
        {
                AdvOnLink on;
                AdvAutonomous on;
        };
};

Now we add 2001:db8:0:f101::1 to br0 using the command below. To keep the changes at boot add it to the /etc/init.d/S40network script. If the release is kamikaze, ip6addr theaddress/theprefixlength is an interface option in /etc/config/network. Forwarding of our delegated /64 subnet to br0 is done automatically in S51radvd

ip -6 addr add 2001:db8:0:f101::1/64 dev br0

In the /etc/init.d/S51radvd we have to add an route in case the aiccu is used:

ip -6 route add 2001:db8:0:f101::1/64 dev br0

After all this you can start the daemon:

/etc/init.d/S51radvd start

You can listen to its advertisments via the radvdump program.

6. Example for debugging purposes

Interface configuration:

root@OpenWrt:~# ip addr show
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0f:66:56:ee:6f brd ff:ff:ff:ff:ff:ff
    inet6 fe80::20f:66ff:fe56:ee6f/64 scope link
3: eth1: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0f:66:56:ee:71 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::20f:66ff:fe56:ee71/64 scope link
4: sit0@NONE: <NOARP> mtu 1480 qdisc noop
    link/sit 0.0.0.0 brd 0.0.0.0
5: br0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:0f:66:56:ee:6f brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/24 brd 192.168.1.255 scope global br0
    inet6 2001:6f8:309:1::1/64 scope global
    inet6 fe80::20f:66ff:fe56:ee6f/64 scope link
6: vlan0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc noqueue
    link/ether 00:0f:66:56:ee:6f brd ff:ff:ff:ff:ff:ff
    inet6 fe80::20f:66ff:fe56:ee6f/64 scope link
7: vlan1: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc noqueue
    link/ether 00:0f:66:56:ee:70 brd ff:ff:ff:ff:ff:ff
    inet 212.68.233.114/24 brd 212.68.233.255 scope global vlan1
    inet6 fe80::20f:66ff:fe56:ee70/64 scope link
8: sixxs@NONE: <POINTOPOINT,NOARP,UP> mtu 1280 qdisc noqueue
    link/sit 212.68.233.114 peer 212.100.184.146
    inet6 2001:6f8:202:e::2/64 scope global
    inet6 fe80::d444:e972/64 scope link
    inet6 fe80::c0a8:101/64 scope link

Routing table:

root@OpenWrt:~# ip route show
192.168.1.0/24 dev br0  proto kernel  scope link  src 192.168.1.1
212.68.233.0/24 dev vlan1  proto kernel  scope link  src 212.68.233.114
default via 212.68.233.1 dev vlan1
root@openwrt:~# ip -6 route show
2001:6f8:202:e::/64 via :: dev sixxs  metric 256  mtu 1280 advmss 1220
2001:6f8:309:1::/64 dev br0  metric 256  mtu 1500 advmss 1220
fe80::/64 dev eth0  metric 256  mtu 1500 advmss 1220
fe80::/64 dev vlan0  metric 256  mtu 1500 advmss 1220
fe80::/64 dev eth1  metric 256  mtu 1500 advmss 1220
fe80::/64 dev br0  metric 256  mtu 1500 advmss 1220
fe80::/64 dev vlan1  metric 256  mtu 1500 advmss 1220
fe80::/64 via :: dev sixxs  metric 256  mtu 1280 advmss 1220
ff00::/8 dev eth0  metric 256  mtu 1500 advmss 1220
ff00::/8 dev vlan0  metric 256  mtu 1500 advmss 1220
ff00::/8 dev eth1  metric 256  mtu 1500 advmss 1220
ff00::/8 dev br0  metric 256  mtu 1500 advmss 1220
ff00::/8 dev vlan1  metric 256  mtu 1500 advmss 1220
ff00::/8 dev sixxs  metric 256  mtu 1280 advmss 1220
default via 2001:6f8:202:e::1 dev sixxs  metric 1024  mtu 1280 advmss 1220

Interface configuration of a client machine:

~$ ip addr show
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: sit0: <NOARP> mtu 1480 qdisc noop
    link/sit 0.0.0.0 brd 0.0.0.0
3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:11:2f:1e:bf:65 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.42/24 brd 192.168.1.255 scope global eth0
    inet6 2001:6f8:309:1:211:2fff:fe1e:bf65/64 scope global dynamic
       valid_lft 2591812sec preferred_lft 604612sec
    inet6 fe80::211:2fff:fe1e:bf65/64 scope link
       valid_lft forever preferred_lft forever

7. Using IPv6 by default with Windows XP

Now you have 6to4 installed on your OpenWrt router with a radvd server, you can enable IPv6 on your Windows box by typing

netsh interface ipv6 install

at the command prompt. This will install IPv6 and you will get a 6to4 address. However Windows will only use it to communicate with other 6to4 addresses or other IPv6 only hosts by default (it will prefer IPv4 otherwise). To force IPv6 with dual stack non-6to4 hosts, use this:

C:\>netsh
netsh>interface ipv6
netsh interface ipv6>show prefixpolicy
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
         5      5  3ffe:831f::/32
        10      4  ::ffff:0:0/96
        20      3  ::/96
        30      2  2002::/16
        40      1  ::/0
        50      0  ::1/128
netsh interface ipv6>set prefixpolicy
One or more essential parameters were not entered.
Verify the required parameters, and reenter them.
The syntax supplied for this command is not valid. Check help for the correct syntax.
Usage: set prefixpolicy [prefix=]<IPv6 address>/<integer> [precedence=]<integer>
             [label=]<integer> [[store=]active|persistent]
Parameters:
       Tag              Value
       prefix         - Prefix for which to add a policy.
       precedence     - Precedence value for ordering.
       label          - Label value for matching.
       store          - One of the following values:
                        active: Change only lasts until next boot.
                        persistent: Change is persistent (default).
Remarks: Modifies a source and destination address selection policy
         for a given prefix.
Example:
       set prefixpolicy ::/96 3 4
netsh interface ipv6>set prefixpolicy ::1/128 50 0
Ok.
netsh interface ipv6>set prefixpolicy ::/0 40 1
Ok.
netsh interface ipv6>set prefixpolicy 2002::/16 30 1
Ok.
netsh interface ipv6>set prefixpolicy ::/96 20 3
Ok.
netsh interface ipv6>set prefixpolicy ::ffff:0:0/96 10 4
Ok.
netsh interface ipv6>set prefixpolicy 3ffe:831f::/32 5 5
Ok.
netsh interface ipv6>show prefixpolicy
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
         5      5  3ffe:831f::/32
        10      4  ::ffff:0:0/96
        20      3  ::/96
        30      1  2002::/16
        40      1  ::/0
        50      0  ::1/128
netsh interface ipv6>exit
C:\>

Notice how the same label is used for both 6to4 (2002::/16) and normal IPv6 (::/0) telling Windows they can be used together at each end of a communication link. Now if you go to an IPv6 enabled website (e.g. www.kame.net) you will connect to it using IPv6 instead of IPv4.

8. Using IPv6 by default with Windows Vista

Even though Vista comes pre-configured with IPv6 support it still only uses the stack to communicate with other 6to4 addresses or other IPv6 only hosts by default (it will prefer IPv4 otherwise). To force IPv6 with dual stack non-6to4 hosts the instructions are the same as above in the Windows XP howto with a couple minor differences. The "set prefixpolicy" command only works once, wiping out all other policies in the process. To recreate these policies you have to use the "add prefixpolicy" command. Also to show the current policies, you need to use the "show prefixpolicies" command instead of "show prefixpolicy".

Short method to editing policies:

C:\>netsh
netsh>interface ipv6
netsh interface ipv6>show prefixpolicies
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
        50      0  ::1/128
        40      1  ::/0
        30      2  2002::/16
        20      3  ::/96
        10      4  ::ffff:0:0/96
         5      5  2001::/32
netsh interface ipv6>delete prefixpolicy 2001::/32
Ok.
netsh interface ipv6>add prefixpolicy 3ffe:831f::/32 5 5
Ok.
netsh interface ipv6>show prefixpolicies
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
        50      0  ::1/128
        40      1  ::/0
        30      2  2002::/16
        20      3  ::/96
        10      4  ::ffff:0:0/96
         5      5  3ffe:831f::/32
netsh interface ipv6>exit
C:\>

Long method:

C:\>netsh
netsh>interface ipv6
netsh interface ipv6>show prefixpolicies
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
        50      0  ::1/128
        40      1  ::/0
        30      2  2002::/16
        20      3  ::/96
        10      4  ::ffff:0:0/96
         5      5  2001::/32
netsh interface ipv6>set prefixpolicy ::1/128 50 0
Ok.
netsh interface ipv6>add prefixpolicy ::/0 40 1
Ok.
netsh interface ipv6>add prefixpolicy 2002::/16 30 1
Ok.
netsh interface ipv6>add prefixpolicy ::/96 20 3
Ok.
netsh interface ipv6>add prefixpolicy ::ffff:0:0/96 10 4
Ok.
netsh interface ipv6>add prefixpolicy 3ffe:831f::/32 5 5
Ok.
netsh interface ipv6>show prefixpolicies
Querying active state...
Precedence  Label  Prefix
----------  -----  --------------------------------
        50      0  ::1/128
        40      1  ::/0
        30      2  2002::/16
        20      3  ::/96
        10      4  ::ffff:0:0/96
         5      5  3ffe:831f::/32
netsh interface ipv6>exit
C:\>

9. Links

10. ToDo

list of IPv6 ready application available in OpenWrt
start/stop radvd when connection goes up/down
add firewall rules for incoming IPv6 connections

11. Questions

How would i go about setting up radvd to announce an v6 address (6to4), derived from an DHCP assigned v4 address (it changes every few weeks)?

change the prefix in the radvd.conf (first 3 sections) to 0, so 2001:db8:0:f101::/64 becomes 0:0:0:f101::/64, and add "Base6to4Interface ppp0;" (where ppp0 is your wan interface) to the section, and set AdvValidLifetime and AdvPreferredLifetime to a low number, so if the v4 address changes, the v6 routing info will be updated quickly, so the finished section would look something like this:

        prefix 0:0:0:f101::/64
        {
                AdvOnLink on;
                AdvAutonomous on;
                Base6to4Interface ppp0;
                # Very short lifetimes for dynamic addresses
                AdvValidLifetime 300;
                AdvPreferredLifetime 120;
        };

That assumes ppp0 is your wan interface, and that you have a /48 address (according to http://ezine.daemonnews.org/200101/6to4.html you do get one with 6to4)