IPv6 hosts configure default route with router’s link-local address

ipv6link-localndpradvd

I have recently added IPv6 to our network as per the instructions at http://www.chronos-tachyon.net/reference/debian-ipv6-and-hurricane-electric.

However, the hosts on the network automatically configure the default route to the link-local address of the router instead of the global address.

The article at http://ipvsix.me/?p=88 says:

You will find that on the LAN host, their default route and gateway
point to the Link-Local address of eth1 on the Linux machine acting as
the IPv6 gateway/router. This is entirely normal and expected.

My problem is that the router (running a derivation of Debian) does not respond to NDP requests for its link-local address because it has a global address configured.

Is there any way to either:

Get the hosts to automatically use the global address of the router for the default host, or
Get the router to reply to NDP requests for its link-local address.

/etc/radvd.conf on the router:

interface eth0 {
    AdvSendAdvert on;
    AdvLinkMTU 1480;
    MinRtrAdvInterval 60;
    MaxRtrAdvInterval 180;
    prefix 2001:xxxx:xxxx:xxxx::1/64 {
        AdvRouterAddr on;
        AdvPreferredLifetime 600;
        AdvValidLifetime 3600;
    };
    route ::/0 {
    };
    RDNSS 2001:xxxx:xxxx:xxxx::2 {};
};

Best Answer

IPv6 back-to-back routing is entirely based on link-local addresses as a consequence it is normal to see the router considering the gateway link-local.

Even if you use IPv6 global addresses, devices will do layer2 resolution using Network Discovery to get the link-local addresses.

Related Solutions

Multiple IPv6 routers in a local network

This configuration won't work with radvd, and my attempts came from a misunderstanding of the purpose of router advertisements. This protocol is meant for host autoconfiguration and not for route propagation between routers.

Replacing radvd with Quagga and an IPv6-enabled routing protocol solves the issue.

Freebsd – Router advertisement for ipv6 is advertising link-local adress

The link local address should work just fine, and is indeed the address used by rtadvd.

I'm using 6to4, but it's essentially the same configuration. In my case all I do is:

ifconfig stf0 create
ifconfig stf0 inet6 2002:c0a8:1:ffff::1/16
ifconfig lan0 inet6 2002:c0a8:1::1/64

This just creates the connection, your tunnel should sever the same purpose.

route add -inet6 default 2002:c058:6301::

At this point ping6 ipv6.google.com works from my router.

sysctl net.inet6.ip6.forwarding=1

Now routing is enabled, even with link local addresses, if I manually configure clients to use the router as their DG IPv6 works. But we want some level of auto-configuration... so /etc/rtadvd.conf contains:

lan0:\
    :addr="2002:c0a8:1::":prefixlen=64:tc=ether:

The only thing left is to add the configuration to my rc.conf file:

ipv6_gateway_enable="YES"               # Route IPv6 Traffic
rtadvd_enable="YES"                     # IPv6 Router Advertisement Daemon
rtadvd_interfaces="lan0"

cloned_interfaces="stf0"
ifconfig_stf0_ipv6="inet6 2002:c0a8:1:ffff::1/16"

ipv6_defaultrouter="2002:c058:6301::"   # 6to4 Default Router

The clients do have a default route of the fec0:: range, but it works perfectly. A tcpdump shows the clients sending from their global IPv6 address to the fec0 address.

For anyone reading this wanting to do 6to4 the above "internal" addresses are for 192.168.0.1, which isn't routable on the Internet. You need to calculate your own internal IPv6 address based on your external IPv4 address.

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