anchor.diff:  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.
  +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 random selection based on
  -the routes' weight values to route the packets.
  +* For packets with more than one matching route, uses per-agent round robin
  +selection among those routes. 
   
  -* For packets that don't match routes with matching sources and destinations,
  -drops these packets.
  +* Drops packets that don't match routes with matching sources and destinations.
   
   The router uses information in the following fields in the routing table:
   
  
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: re-write the packet's destination MAC address before emitting it towards the
  intermediate router.
  
  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
  