RFC 2080 (rfc2080) - Page 3 of 19

RIPng for IPv6

RFC 2080                     RIPng for IPv6                 January 1997


   Information Protocol, with XNS addresses replaced by a more general
   address format capable of handling IPv4 and other types of address,
   and with routing updates limited to one every 30 seconds.  Because of
   this similarity, the term Routing Information Protocol (or just RIP)
   is used to refer to both the XNS protocol and the protocol used by
   routed.

1.1  Theoretical Underpinnings

   An introduction to the theory and math behind Distance Vector
   protocols is provided in [1].  It has not been incorporated in this
   document for the sake of brevity.

1.2  Limitations of the Protocol

   This protocol does not solve every possible routing problem.  As
   mentioned above, it is primarily intended for use as an IGP in
   networks of moderate size.  In addition, the following specific
   limitations are be mentioned:

   - The protocol is limited to networks whose longest path (the
     network's diameter) is 15 hops.  The designers believe that the
     basic protocol design is inappropriate for larger networks.  Note
     that this statement of the limit assumes that a cost of 1 is used
     for each network.  This is the way RIPng is normally configured.
     If the system administrator chooses to use larger costs, the upper
     bound of 15 can easily become a problem.

   - The protocol depends upon "counting to infinity" to resolve certain
     unusual situations (see section 2.2 in [1]).  If the system of
     networks has several hundred networks, and a routing loop was formed
     involving all of them, the resolution of the loop would require
     either much time (if the frequency of routing updates were limited)
     or bandwidth (if updates were sent whenever changes were detected).
     Such a loop would consume a large amount of network bandwidth
     before the loop was corrected.  We believe that in realistic cases,
     this will not be a problem except on slow lines.  Even then, the
     problem will be fairly unusual, since various precautions are taken
     that should prevent these problems in most cases.

   - This protocol uses fixed "metrics" to compare alternative routes.
     It is not appropriate for situations where routes need to be chosen
     based on real-time parameters such a measured delay, reliability,
     or load.  The obvious extensions to allow metrics of this type are
     likely to introduce instabilities of a sort that the protocol is
     not designed to handle.





Malkin & Minnear            Standards Track