Show pagesourceOld revisionsBacklinksBack to top × Table of Contents IPv6 on L2TP softwire About softwires ISP using softwires to provide IPv6 Overview Installation Configuration L2TP tunnel using xl2tpd PPP configuration Prefix delegation through DHCPv6 IPv6 on L2TP softwire This page documents how to configure IPv6 over a L2TP softwire, which is a method used by some ISP to provide IPv6 connectivity. About softwires Softwire is the new fancy term for network tunnels, aka encapsulation. Reasonably accurate definitions about softwires are given in RFC 4925, and RFC 5571 describes an implementation using L2TPv2. Softwires are used as basic blocks to transport newer protocols (typically IPv6) over an older network (typically, the IPv4 core network of an ISP). ISP using softwires to provide IPv6 SFR, in France, is known to use softwires to provide IPv6 to its residential customers. See some documentation (in French). Overview 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. Installation You need to install xl2tpd, which will handle the L2TP tunnel and PPP session. Configuration # /etc/config/network 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' If you need authentication at the L2TP level (before PPP): # /etc/xl2tpd/xl2tp-secrets * * 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 ifstatus wan6). 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. L2TP tunnel using xl2tpd # /etc/x2ltpd/x2ltpd.conf [global] port = 1701 auth file = /etc/xl2tpd/xl2tp-secrets access control = no [lac 6pe] lns = 109.6.3.95 ; 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 # /etc/xl2tpd/xl2tp-secrets * * 6pe Starting the L2TP tunnel 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: # /etc/rc.d/S60xl2tpd ... (sleep 10 && echo "c 6pe" > /var/run/xl2tpd/l2tp-control) & $BIN $OPTIONS ... Troubleshooting look at the logs (logread) try to activate some xl2tpd debug options use tcpdump to see what's going on with the LNS PPP configuration Last, you need to set PPP options for IPv6 negotiation. # /etc/ppp/options.xl2tpd # 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 dhcp/XX.XX.XX.XX@YYYYYYYYYYYY, where 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 /etc/ppp/chap-secrets: #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. Prefix delegation through DHCPv6 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 wide-dhcp6c client. OpenWrt integration Note that this is specific to Attitude Adjustment, as IPv6 support is expected to changed a lot in the upcoming Barrier Breaker release. Interface declaration We need to tell OpenWrt about the new interface: # /etc/config/network config interface wan6 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, where the gateway is the link-local address of the router at the other end of the softwire: # /etc/config/network config route6 option interface wan6 option target '::/0' option gateway 'fe80::XXXX:XXff:feXX:XXXX' This website uses cookies. By using the website, you agree with storing cookies on your computer. Also you acknowledge that you have read and understand our Privacy Policy. If you do not agree leave the website.OKMore information about cookies Last modified: 2021/11/15 08:05by vgaetera