DS-Lite configuration is not working with the OpenWrt router behind Fritz!Box

Installing and Using OpenWrt Network and Wireless Configuration
1

Hi OpenWrt community

Unfortunately, I came to know about the OpenWrt bit late, several weeks ago and I am really happy with all the customisations that I can do with that.

Fortunately, my own connection is still utilising the dual-stack which means I am getting a public IPv4 address and a public IPv6 prefix. But several days ago one of my friend's connections was upgraded to DS-Lite which means he is not getting any public IPv4 address at all. According to the ISP most probably my connection will be upgraded soon or later. Therefore I have to be ready with that.

I was using Fritz!Box as my main modem router before getting to know the OpenWrt and I want to use the Fritz!Box further as the interface for the DSL for several reasons even though I am aware of replacing the Fritz!Box with a modem or use the Fritz!Box with bridge mode.

My current setup is as follows:

Internet (1&1 with DS-Lite) → Fritz!Box → OpenWrt router (exposed host) → Lan

The internet is provided by the 1&1 and I am (in this case my friend) getting only a public IPv6 address prefix and not any public IPv4 address.

The Fritz!Box is having only one client which is the OpenWrt router as an exposed host which is more or less equivalent to DMZ.

The Raspberry Pi based OpenWrt with the second USB 3.0 ethernet port which is facing the WAN in my case the Fritz!Box, and the built-in ethernet is connected to a 24 port Netgear managed switch.

My setup is as follows and I have created the wan6_4 interface manually.

config interface 'loopback'
    option device 'lo'
    option proto 'static'
    option ipaddr '127.0.0.1'
    option netmask '255.0.0.0'

config globals 'globals'
    option ula_prefix '[hidden]'
    option packet_steering '1'

config device
    option name 'br-lan'
    option type 'bridge'
    list ports 'eth0'

config interface 'lan'
    option proto 'static'
    list ipaddr '10.0.0.1/24'
    option ip6weight '200'
    option ip6assign '60'
    option device 'eth0'

config interface 'WAN'
    option proto 'static'
    option netmask '255.255.255.0'
    option device 'eth1'
    option ipaddr '192.168.178.10'
    option ip6weight '100'
    option ip6assign '60'
    option gateway '192.168.178.1'

config interface 'WAN6'
    option proto 'dhcpv6'
    option device 'eth1'
    option reqaddress 'try'
    option ip6weight '200'
    option ip6assign '60'
    option reqprefix '56'

config interface 'wan6_4'
    option proto 'dslite'
    option encaplimit 'ignore'
    option tunlink 'WAN6'
    option peeraddr '::' // A real value

The WAN is disabled during the test and unfortunately, I could not ping 1.1.1.1and I will appreciate any help.

Thanks in advance
Goppinath

2

Hi! Did you find a solution for you issue? I'm currently facing a similar issue and I'm looking for any inputs on solving it.

3

Thanks, @cupora for reminding my question which I forget to answer my question even after two years.

First of all the scenario or the use-case elaborated above is conceptionally wrong because according to the OpwnWrt documentation, my OpenWrt is acting as a router but not as a gateway.

Definition: If a device facing a modem or has an integrated modem then it is the gateway on the other hand the device that is facing a gateway is a router.

Source: https://openwrt.org/docs/guide-user/network/switch_router_gateway_and_nat#openwrt_roles

The DS-Lite setup in the OpenWrt makes sense only if the OpenWrt acting as a gateway but not as a router.

Supplying the dual-stack (IPv4 and IPv6) down to the downstream routers is the sole duty of the gateway or the upstream router, in this example, the FritzBox which acts as a modem gateway.

OpenWrt has to be coupled to the FritzBox via the wan4 and wan6 interfaces and delegate the dual-stack further to the downstream routers or the clients.

As long as the FritzBox is getting the /56 public IPv6 prefix (Most of the German ISPs) it can delegate the /57 prefix to the OpenWrt in general. In contrast to the IPv6, the FritzBox is getting an IPv4 from the 100.64.0.0/10 CGNAT subnet because of the DS-Lite. Therefore FritzBox has to use the NAT to delegate the IPv4 addresses further down with the 192.168.178.0/24 subnet.

The wan6 interface will get one public IPv6 address and the PD and the wan4 interface will get one IPv4 from the FritzBox 192.168.178.0/24 subnet.

Additionally, just to avoid the double NAT the OpenWrt has to be the exposed host to the FritzBox.

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