How to add ipv6 default route

I have the following setup

           Linux 1                      Linux 0
    eth1            eth0-------------------eth0
   14.14.14.80      19.19.19.20             19.19.19.10
   2005::5/64       2004::3/64              2001::3/64 

From Linux0, i am able to ping 14.14.14.80 or 19.19.19.20 ( 19.19.19.20 was added as a default GW) and also on Linux1, ipv4 forwarding was enabled.
For ipv6, i cannot add 2004::3/64 as the default ipv6 gateway on Linux0.
I tried

ip -6 route add default via 2004::3

and

ip -6 route add default via 2004::

But i get the error

RTNETLINK answers: No route to host

What am i missing here?.