OVH provides native IPv6 at gra2, so we don't need a HE tunnel.
Routing is slightly more complex as the gateway does NOT belong to our range,
we use a similar configuration than IPFO with two routes, the first to reach
the gateway, the second default one through that gateway.
To determine if we're in such case can be done with code introduced in D3077.
On FreeBSD, to find the gateway through NDP (neighbor discovery protocol)
produces until 13.1 the following error (here with ping):
ping6: sendmsg: No buffer space available ping6: wrote www.google.com 16 chars, ret=-1
As such, this routing "as is" without any NDP fix requires FreeBSD 13.2+
to benefit from https://reviews.freebsd.org/D23695 change.
References:
- https://en.wikipedia.org/wiki/Neighbor_Discovery_Protocol
- https://datatracker.ietf.org/doc/html/rfc5942 (Introduction and RFC 5942 4.1)
- https://reviews.freebsd.org/D23695
Ref T1853