I'm trying to configure NetworkManager to perform the following action for an interface
ip route add ::/0 dev he-ipv6
he-ipv6 is a point-to-point ipv4 sit mode tunnel and running the above command directly works. Unfortunately when the device is rebooted the default gateway is not reconfigured and therefore all IPv6 traffic outside the network is dropped.
I've tried configuring a manual route via:
nmcli c modify he-ipv6 ipv6.routes '::/0'
but of course nmcli will not let you configure static routes for the default gateway.
Error: failed to modify ipv6.routes: invalid prefix '0'; <1-128> allowed.
StackExchange (https://unix.stackexchange.com/questions/320943/add-default-route-without-gateway-nmcli)
Fedora's IPv6 HOWTO contains a section on he.net and NetworkManager - https://fedoraproject.org/wiki/IPv6_tunnel_via_Hurricane_Electric (https://fedoraproject.org/wiki/IPv6_tunnel_via_Hurricane_Electric):
nmcli connection add type ip-tunnel con-name sit1 ifname sit1 mode sit \
remote SERVER_IPV4_ADDRESS -- ipv4.method disabled ipv6.method manual \
ipv6.address CLIENT_IPV6_ADDRESS ipv6.gateway SERVER_IPV6_ADDRESS \
ip-tunnel.ttl 64
HTH