A routing circuit reachable address entity contains information about a
   manually entered address prefix accessible over that circuit. It exists only
   on L2 routers and end nodes. On L2 routers the type may be outbound or
   inbound. A reachable address of type outbound default describes address
   prefixes in an external domain that are reachable by outbound traffic over
   this circuit. The routing information contained in the reachable address is
   entered directly into the L2 decision process. When ManualL2Algorithm has
   the value routing vector, only reachable addresses with address prefixes
   corresponding to Phase IV areas are fed into the decision process.

   An inbound reachable address describes address prefixes corresponding to
   Phase IV areas which are reachable through the local node by inbound traffic
   over this circuit. The routing information contained in the reachable address
   area and cost is entered into a Phase IV routing vector message, which is
   transmitted periodically over this circuit.

   On an end system the type may be outbound or for a broadcast circuit only
   filter. A reachable address of type outbound behaves in a similar way to that
   on an L2 router except that the routing information is used to control the
   operation of the ES cache. A reachable address of type filter is used to
   specify the permitted LAN address of routers on the LAN which will be used by
   the cache algorithm.

   The circuit-name refers to the circuit associated with the specified
   reachable address.  The address-prefix refers to the reachable address
   managed by this command.