Have you turned on IPv6 forwarding?
echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
Yes, but it does not help...

Today I tried this, too:
On the server:
ip=$(dig +short lucabert.homelinux.org)
/sbin/ip tunnel add ipv6tun mode sit ttl 255 remote $ip local 84.200.210.163
/sbin/ip link set dev ipv6tun up
/sbin/ip -6 route add 2001:1608:10:47:10::/80 dev ipv6tun metric 1
On my PC:
IPLOCAL=`/sbin/ip addr show dev ppp0 | /bin/grep inet | /usr/bin/awk '{print $2}'`
/sbin/ip tunnel add ipv6tun mode sit remote 84.200.210.163 local $IPLOCAL ttl 255
/sbin/ip link set ipv6tun up
/sbin/ip route add ::/0 dev ipv6tun
/sbin/ip -6 addr add 2001:1608:10:47:10::1/80 dev eth0
Well, from my Server I can reach my PC and from my PC I can reach the Server, but again, when I try, from my PC, to reach any other Host, I can't get an answer:
tcpdump on my PC (tcpdump -n -i ipv6tun), when I try to ping 2001:1608:10:47::1:
08:22:49.630898 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 1, length 64
08:22:50.639091 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 2, length 64
08:22:51.639103 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 3, length 64
08:22:52.639104 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 4, length 64
08:22:53.639106 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 5, length 64
08:22:54.639102 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 6, length 64
08:22:55.639104 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 7, length 64
tcpdump on my Server (tcpdump -n -i eth0 ip6 and not port 22):
08:22:49.247589 IP6 fe80::c955:68cb:cc9d:fd72.546 > ff02::1:2.547: dhcp6 solicit
08:22:49.656513 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 1, length 64
08:22:49.752588 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:50.264218 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 117
08:22:50.264490 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 119
08:22:50.664686 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 2, length 64
08:22:50.665120 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:51.191265 IP6 fe80::2c8c:e070:d9ca:60ed.546 > ff02::1:2.547: dhcp6 solicit
08:22:51.247685 IP6 fe80::c955:68cb:cc9d:fd72.546 > ff02::1:2.547: dhcp6 solicit
08:22:51.664687 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 3, length 64
08:22:51.665089 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:51.777848 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 146
08:22:52.033862 IP6 fe80::64c7:cf29:b6af:44c5.546 > ff02::1:2.547: dhcp6 solicit
08:22:52.197662 IP6 fe80::2c8c:e070:d9ca:60ed.546 > ff02::1:2.547: dhcp6 solicit
08:22:52.413032 IP6 fe80::905:2ba0:3b63:5abc.546 > ff02::1:2.547: dhcp6 solicit
08:22:52.664719 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 4, length 64
08:22:53.275399 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 119
08:22:53.275568 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 117
08:22:53.664928 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 5, length 64
08:22:53.751755 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:53.957689 IP6 fe80::b8de:b220:8274:46b5.60560 > ff02::1:3.5355: UDP, length 22
08:22:54.211661 IP6 fe80::2c8c:e070:d9ca:60ed.546 > ff02::1:2.547: dhcp6 solicit
08:22:54.654328 IP6 fe80::e269:95ff:feb3:e4ec > 2001:1608:10:24::1: ICMP6, neighbor solicitation, who has 2001:1608:10:24::1, length 32
08:22:54.657554 IP6 fe80::223:9c00:f0fc:6fc0 > fe80::e269:95ff:feb3:e4ec: ICMP6, neighbor advertisement, tgt is 2001:1608:10:24::1, length 24
08:22:54.664670 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 6, length 64
08:22:54.665027 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:54.787263 IP6 fe80::2c8c:e070:d9ca:60ed.59494 > ff02::c.1900: UDP, length 146
08:22:54.830667 IP6 fe80::2002:4895:807b:75e7.546 > ff02::1:2.547: dhcp6 solicit
08:22:55.247875 IP6 fe80::c955:68cb:cc9d:fd72.546 > ff02::1:2.547: dhcp6 solicit
08:22:55.664690 IP6 2001:1608:10:47:10::1 > 2001:1608:10:47::1: ICMP6, echo request, seq 7, length 64
08:22:55.665099 IP6 2001:1608:10:47::1 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:1608:10:47:10::1, length 32
08:22:55.825708 IP6 fe80::383e:8dda:5a62:671b.546 > ff02::1:2.547: dhcp6 solicit
08:22:55.914350 IP6 2001:1608:10:24:1::1.110 > 2001:470:1f0b:191:20b:6aff:fe73:a7cb.59568: Flags [S.], seq 28950079, ack 2257202300, win 5712, options [mss 1440,sackOK,TS val 198682843 ecr 1114510126,[|tcp]>
08:22:55.915935 IP6 2001:1608:10:24:1::1.110 > 2001:470:1f0b:191:20b:6aff:fe73:a7cb.59568: Flags [S.], seq 28950079, ack 2257202300, win 5712, options [mss 1440,sackOK,TS val 198682843 ecr 1114510126,[|tcp]>
Well, I can't understand WHY it does not work... Why ask my Server who has 2001:1608:10:47:10::1, if it can reach it using device ip6tun?
Thanks a lot for your help
Luca Bertoncello