In 06aa65e1ba (#10627) a new behavior was
introduced in IPv6 route resolution to try address resolution only at
interfaces that have the prefix of the address to be resolved configured
in the prefix list. This however only makes sense, if the prefix
configured is [on-link], otherwise there is small likelihood of the
address to be resolved being on that link.
For the error case presented for 06aa65e (circular routing at the border
router) this made sense, however within a 6LoWPAN, due to the prefix
being valid for the entire mesh, this leads to the nodes always trying
classic address resolution for in-network addresses instead of just
routing to the default route.
Classic address resolution however fails, as 6LoWPAN hosts typically
[don't join the solicited-node multicast address of their unicast
addresses][6LN-iface-init], resulting in in-network addresses not being
reachable.
As such, to prevent both error cases
- the fallback to address resolution by prefix list must only be used
when the prefix is on-link,
- the prefix configured by DHCPv6/UHCP at the 6LoWPAN border router
must be configured as on-link, but
- the prefix must not be advertised as on-link within the 6LoWPAN to
still be [in line with RFC 6775][RFC-6775-forbidden]
With this change these cases are covered.
[on-link]: https://tools.ietf.org/html/rfc4861#page-6
[RFC 6775]: https://tools.ietf.org/html/rfc6775
[6LN-iface-init]: https://tools.ietf.org/html/rfc6775#section-5.2
[RFC-6775-forbidden]: https://tools.ietf.org/html/rfc6775#section-6.1
4fc0251b4b