datun is an interface used as one of the edges in a 6in4 tunnel set with
ip tunnel add datun mode sit remote 192.0.2.49 local 198.51.100.50 ttl 64 ip link set datun up
# ifconfig datun datun Link encap:IPv6-in-IPv4
and taken down with
# ip link set datun downat the 6in4 tunnels to the IPv6 Internet how-to, even in places we needed to delete the tunnel instead of putting it down, causing all kinds of errors and confusion.
To delete a tunnel interface.
ip tunnel del datun
Instead of "restarting" the 6in4 tunnel it may be better to destroy it and set it again.
# ip tunnel del datun # /etc/network/if-up.d/ipv6-tunnel.sh
delete tun interface