This page documents how to configure IPv6 over a L2TP softwire, which is a method used by some ISP to provide IPv6 connectivity. It assumes Barrier Breaker (OpenWRT 14.07), but the old configuration for Attitude Adjustment (12.09) is available at the end of the page.
Softwires are used as basic blocks to transport newer protocols (typically IPv6) over an older network (typically, the IPv4 core network of an ISP).
- SFR, in France, is known to use softwires to provide IPv6 to its residential customers. See some documentation (in French).
This howto is derived from an experience with SFR, in France (FTTH residential access). It might applies to other ISPs as well, but you'll need to adapt IP addresses, PPP login and passwords, and so on.
The high-level description of the tunneling is the following:
- a L2TP tunnel is created, encapsulated in UDP packets over IPv4
- a PPP session is established inside the tunnel
- IPv6CP (see RFC 5072) is used to negotiate link-local IPv6 addresses
- an IPv6 prefix is obtained thanks to DHCPv6
In the case of SFR, steps 1 and 2 require an authentication. Fortunately, the L2TP password is hardcoded. The PPP password is not, but it's sent as cleartext, so a simple sniffing is enough to recover it.
Barrier Breaker has native IPv6 support, which greatly simplifies the configuration.
You need to install
xl2tpd, which will handle the L2TP tunnel and PPP session.
config interface 6pe option proto l2tp option server <LNS address> option username '<PPP username>' option password '<PPP password>' option keepalive '6' option ipv6 '1' config interface 'wan6' option ifname '@6pe' option proto 'dhcpv6'
For the RC3 version of Barrier Breaker, you should use
proto l2tpv2 instead.
See protocol.l2tp.ppp.over.l2tp.pseudowire.tunnel for more options.
If you need authentication at the L2TP level (before PPP), configure it in
* * my_l2tp_password
At this point, rebooting or simply running
ifup wan6 should give you a fully working IPv6 setup. To debug, look at the logs (
logread) and the interfaces status (
ifstatus 6pe and
This setup is doing everything "by hand", which might be useful for other Linux distribution as well (for instance, Debian). More precisely, we do the following:
xl2tpdto negociate the L2TP tunnel and the PPP session: this creates a
dhcp6cto request an IPv6 prefix through DHCPv6
radvdto distribute addresses to LAN clients from a /64 (which is automatically taken from the delegated prefix)
Of course, you are free to use other methods. Most notably, newer OpenWRT versions handle IPv6 differently. It's also possible to distribute IPv6 addresses to LAN clients using
Note that SFR's CPE, the Neufbox, is running a modified version of OpenWRT. Since they publish their firmware (I used the NB6-MAIN-R3.3.4 firmware), it's possible to look at their config files (and hardcoded passwords), which greatly simplifies the task.
You need to install
xl2tpd. Then, a working
/etc/x2ltpd/x2ltpd.conf for SFR is:
[global] port = 1701 auth file = /etc/xl2tpd/xl2tp-secrets access control = no [lac 6pe] lns = 188.8.131.52 ; address of the LNS (L2TP Network Server) ppp debug = yes hostname = XX.XX.XX.XX ; your public IP address hidden bit = no ; ppp debug = yes pppoptfile = /etc/ppp/options.xl2tpd require authentication = no refuse authentication = no refuse chap = no flow bit = yes length bit = yes
You need to fill out
/etc/xl2tpd/xl2tp-secrets with the password. In the case of SFR:
* * 6pe
This should be enough to see if it works or not.
You need to start
xl2tpd, and connect the profile we defined:
/etc/init.d/xl2tpd start echo "c 6pe" > /var/run/xl2tpd/l2tp-control
There doesn't seem to be an easy way to start a profile automatically at startup. Quick & dirty: edit
/etc/rc.d/S60xl2tpd and add
(sleep 10 && echo "c 6pe" > /var/run/xl2tpd/l2tp-control) &
just before the
$BIN $OPTIONS line.
- look at the logs (
- try to activate some
tcpdumpto see what's going on with the LNS
Last, you need to set PPP options for IPv6 negotiation. In
# From the official firmware ipv6 , +ipv6 ipv6cp-use-persistent lock child-timeout 20 lcp-echo-failure 3 lcp-echo-interval 20 name <your PPP login>
For SFR, the PPP login seems to be
XX.XX.XX.XX is your public IP address, and
YYYYYYYYYYYY is the MAC address of the WAN interface of the official box, without the colons.
You then need to define the PPP password in
#USERNAME PROVIDER PASSWORD IPADDRESS dhcp/XX.XX.XX.XX@YYYYYYYYYYYY * <PPP password>
For SFR, the password is not obvious. It's sent in cleartext, thus recoverable by sniffing the WAN port of the official box.
Once the PPP session is established inside the L2TP tunnel, a new interface
ppp0 should appear.
The only remaining step is to request an IPv6 prefix to the ISP, by using for instance the
Note that this is specific to Attitude Adjustment, as IPv6 support is expected to changed a lot in the upcoming Barrier Breaker release.
We need to tell OpenWRT about the new interface, in
config interface wanv6 option ifname ppp0 option proto none
If, at some point, you don't get a default route for IPv6, you could try to add the route yourself:
config route6 option interface wanv6 option target '::/0' option gateway 'fe80::XXXX:XXff:feXX:XXXX'
where the gateway is the link-local address of the router at the other end of the softwire.
Start by modifying the
wan zone in
option network 'wan wanv6'
doc/howto/ipv6.softwire.txt · Last modified: 2014/08/23 03:35 by zorun