anchor.diff:  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
  +Note that routes in normal (that is, physical) routers 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
  
positive.code: 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.
  
  == Type
  
  
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:
  
  