RFC 2081 (rfc2081) - Page 3 of 4

RIPng Protocol Applicability Statement

RFC 2081                  RIP-2 Applicability               January 1997


   The Internal Routers (IR1 and IR2) are only running RIPng.  The
   External Routers (XR1 and XR2) are both running BGP, for example;
   however, only XR1 is running BGP and RIPng.  Since XR2 is not running
   RIPng, the IRs will not know of its existance and will never use it
   as a next hop, even if it is a better next hop than XR1.  Of course,
   XR1 knows this and can indicate, via the Next Hop mechanism, that XR2
   is the better next hop for some routes.

3.4 Authentication

   Authentication, which was added to RIP-2 because RIP-1 did not have
   it, has been dropped from RIPng.  This is safe to do because IPv6,
   which carries the RIPng packets, has build in security which IPv4 did
   not have.

3.5 Packet Length

   By allowing RIPng routing update packets to be as big as possible,
   the number of packets which must be sent for a complete update is
   greatly reduced.  This in no way affects the operation of the
   distance-vector protocol; it is merely a performance enhancement.

3.6 Diameter and Complexity

   The limit of 15 cost-1 hops is a function of the distance-vector
   protocol, which depends on counting to infinity to resolve some
   routing loops.  If infinity is too high, the time it would take to
   resolve, not to mention the number of routing updates which would be
   sent, would be prohibitive.  If the infinity is too small, the
   protocol becomes useless in a reasonably sized network.  The choice
   of 16 for infinity was made in the earliest of RIP implementations
   and experience has shown it to be a good compromise value.

   RIPng will efficiently support networks of moderate complexity.  That
   is, topologies without too many multi-hop loops.  RIPng also
   effeciently supports topologies which change frequently because
   routing table changes are made incrementally and do not require the
   computation which link-state protocols require to rebuild their maps.

4.  Conclusion

   Because the basic protocol is unchanged, RIPng is as correct a
   routing protocol as RIP-2.  RIPng serves the same niche for IPv6 as
   RIP-2 does for IPv4.

5.  Security Considerations

   RIPng security is discussed in section 3.4.



Malkin                       Informational