creating unreachable routes with NetworkManager

[Wolfgang S. Rupprecht]

Back when I ran my server with the networking scripts instead of
NetworkManager it was easy to add unreachable routes.  I'd put lines
like the following:

/etc/sysconfig/network-scripts/route-lo:
unreachable 10.0.0.0/8
unreachable 172.16.0.0/16
unreachable 192.168.0.0/16

/etc/sysconfig/network-scripts/route6-lo:
unreachable fc00::/7

When lo was enabled, I'd get those unreachable routes loaded (and a few
others that the networking scripts added for me.)  Now with
NetworkMisManager I don't get either my unreachalbes or the formerly
built-in ones.

Is there a trick I'm missing?  Obviously I could do an "ip route add"
from a private systemd service, but that seems a bit heavy handed.

(The reason I need to add the unreachables is that my ISP doesn't send
me network unreachables for private addresses.  For laptops on the go,
they sometimes get routable IPv6 addresses as well as unroutable IPv4
addresses.  I use nsupdate to register my laptop's current addresses in
DNS and when private addresses show up it would be nice for things like
"ssh laptop" to quickly move on from the private addresses without a
very long timeout.)

-wolfgang