2. プロトコル定義

   RIPng is intended to allow routers to exchange information for
   computing routes through an IPv6-based network.  RIPng is a distance
   vector protocol, as described in [1].  RIPng should be implemented
   only in routers; IPv6 provides other mechanisms for router discovery
   [10].  Any router that uses RIPng is assumed to have interfaces to
   one or more networks, otherwise it isn't really a router.  These are
   referred to as its directly-connected networks.  The protocol relies
   on access to certain information about each of these networks, the
   most important of which is its metric.  The RIPng metric of a network
   is an integer between 1 and 15, inclusive.  It is set in some manner
   not specified in this protocol; however, given the maximum path limit
   of 15, a value of 1 is usually used.  Implementations should allow
   the system administrator to set the metric of each network.  In
   addition to the metric, each network will have an IPv6 destination
   address prefix and prefix length associated with it.  These are to be
   set by the system administrator in a manner not specified in this


   Each router that implements RIPng is assumed to have a routing table.
   This table has one entry for every destination that is reachable
   throughout the system operating RIPng.  Each entry contains at least
   the following information:

   - The IPv6 prefix of the destination.

   - A metric, which represents the total cost of getting a datagram
     from the router to that destination.  This metric is the sum of the
     costs associated with the networks that would be traversed to get
     to the destination.

   - The IPv6 address of the next router along the path to the
     destination (i.e., the next hop).  If the destination is on one of
     the directly-connected networks, this item is not needed.

   - A flag to indicate that information about the route has changed
     recently.  This will be referred to as the "route change flag."

   - Various timers associated with the route.  See section 2.3 for more
     details on timers.


   The entries for the directly-connected networks are set up by the
   router using information gathered by means not specified in this
   protocol.  The metric for a directly-connected network is set to the
   cost of that network.  As mentioned, 1 is the usual cost.  In that
   case, the RIPng metric reduces to a simple hop-count.  More complex
   metrics may be used when it is desirable to show preference for some
   networks over others (e.g., to indicate of differences in bandwidth
   or reliability).


   Implementors may also choose to allow the system administrator to
   enter additional routes.  These would most likely be routes to hosts
   or networks outside the scope of the routing system.  They are
   referred to as "static routes."  Entries for destinations other than
   these initial ones are added and updated by the algorithms described
   in the following sections.


   In order for the protocol to provide complete information on routing,
   every router in the AS must participate in the protocol.  In cases
   where multiple IGPs are in use, there must be at least one router
   which can leak routing information between the protocols.



Copyright (C) 2006 七鍵 key@do.ai 初版:2006年11月01日 最終更新:2006年11月01日