30-ipforward.conf~ (Source)

# For IPv4 forwarding
net.ipv4.ip_forward=1

# For IPv6 forwarding
net.ipv6.conf.all.forwarding=1

# This is needed because a router "shouldn't" accept
# router advertisements in theory, but in practice,
# this kind of router should.
# 0 = Don't accept (we don't want this)
# 1 = Accept if we're not a router (i.e. forwarding is disabled; we don't want this)
# 2 = Accept even if we're a router (we DO want this)
net.ipv6.conf.eth1.accept_ra=2