Attached hosts

Attached hosts

allow this config to function:
  set int ip address loop0 169.254.1.1/32  (the default GW address for attached hosts)
  set int unnumbered af_packet0 use loop0  ('enable' IP on the host interface)
  ip route add 192.168.1.1/32 via af_packet0 (where to find the host)
repeat for each host and host interface.
Inter-host communication is throught the /32 routes.
To allow this:
 1 - attached host routes have the ATTACHED flag set, so the ARP code accepts then as legitimate sources
 2 - unnumbered interfaces inherit the source address from the IP interface

Change-Id: Ib66c5f0e848c528f79372813adc3a0c11b50717f
Signed-off-by: Neale Ranns <nranns@cisco.com>