Your IPv4 endpoint is unreachable or unstable

[aziaja]

...

[kristiankrohn]

You should allow protocol 41 (IPv6) packets from the HE endpoint:

Code Select Expand

iptables -A INPUT -s $IPv4_of_TunnelBroker -p ipv6 -j ACCEPT

Otherwise IPv6 traffic will only flow if you sent the first packet, in which case your ESTABLISHED,RELATED rule would be used.

[snarked]

Agreed.  Also, your rule:

iptables -I INPUT 1 -s 127.0.0.0/8 -d 127.0.0.0/8 -j ACCEPT

might not be the best choice to permit looped back packets.

Try these:

-A INPUT  -j ACCEPT -i lo
-A OUTPUT -j ACCEPT -o lo

-A INPUT  -j ACCEPT -p ipv6 -s tserv15.lax1.ipv6.he.net  (I use this tunnel)
-A OUTPUT -j ACCEPT -p ipv6 -d tserv15.lax1.ipv6.he.net (you could restrict this further)

and in "/etc/protocols":

ipv6    41      IPV6            # ipv6

You should also get used to using iptables-restore instead of separate commands; it's more efficient for bringing up a firewall all at once.