anchor.diff:  has the longest mask (a.k.a. longest-prefix matching).
   
   . If there's more than one route candidate (with equal destination prefix mask
  -length), use weighted random selection based on the routes' Weight fields.
  +length and weight), use per-agent round robin to select a route.
   
   == Type
   
  
positive.code: re-write the packet's destination MAC address before emitting it towards the
  intermediate router.
  
  Note that normal (that is, physical) routers' routes differ from MidoNet's
  virtual routers in that they don't have a target/destination virtual port (the
  'Normal' route in MidoNet has this; see "Type"). Therefore, normal routers use
  the Next Hop Gateway IP address to determine which port should be used to emit
  
negative.code: For traffic that ingresses a router port, the router does the following:
  
  * Attempts to match a given packet's destination with a route in its routing
  table based on the packet's source and destination, prefering the route with
  the lower weight value.
  
  * For packets with more than one matching route, uses per-agent round robin
  selection among those routes. 
  
  * Drops packets that don't match routes with matching sources and destinations.
  
  The router uses information in the following fields in the routing table:
  
  