Re: NetBSD systems as half-routers for P2P or VPN links

[Ignatios Souvatzis <is%netbsd.org@localhost>]

On Wed, Feb 06, 2013 at 11:01:40PM -0800, Erik Fair wrote:
> Can NetBSD systems in a pair with a point to point link (physical or VPN'd 
> through ... pick your virtual interface) act as half-routers, with the 
> intermediate link being "unnumbered" (to use Cisco parlance)?

For the legacy IP version:

my pppoe up script, also been used earlier on sync ppp over ISDN, has
these lines:

         ifconfig ${PIF} 0.0.0.0 0.0.0.1 link1 up
         route add default 0.0.0.1
                 
Async serial interface pppd supports what you want by giveing the interface
the same address as the machine has anyway, but as point-to-point link.

Of course, with modern IP you can just use the link-name qualified
link-local addresses for point to point links, if you insist to
not make them globally- numbered. Use any address in fe80::/64 but your
local one for the route to the peer and beyond. The disadvantage is
that diagnostics (traceroute6, ping6, or norml-usage failures) might
carry the link-local address back, which wouldn't be useful to a 
remote fellow network administrator.

Regards,
        -is