RFC 2092 (rfc2092) - Page 3 of 6

Protocol Analysis for Triggered RIP

RFC 2092            Triggered RIP Protocol Analysis         January 1997


3.3 Technology Restrictions

   There is a small but nontrivial possiblility of an incorrectly
   configured or poorly operating link causing severe data loss,
   resulting in a 'black hole' in routing. This is often unidirectional
   - the link that route updates cross works properly, but not the
   return path.

   Triggered RIP will NOT fuction properly (and should NOT be used) if a
   routing information will be retained/advertised for an arbitrarily
   long period of time (until an update in the opposite direction fails
   to obtain a response).

   To detect black holes in technologies which use PPP encapsulation,
   either Echo Request/Response or Link Quality Monitoring should be
   used.  When a black hole is detected a circuit down indication must
   be sent to the routing application.

   Current (and future) technologies which do not use PPP, need to use
   an equivalent 'are-you-there' mechanism - or should NOT be used with
   Triggered RIP.

3.4 Presumption of Reachability

   In a stable network there is no requirement to propagate routing
   information on a circuit, so if no routing information is (being)
   received on a circuit it is assumed that:

   o  The most recently received information is accurate.

   o  The intervening path is operational (although there may be no
      current connection).

   If the circuit manager determines that the intervening path is NOT
   operational routing information previously received on that circuit
   is timed out.  It is worth stressing that it can be ANY routed
   datagram which triggers the event.

   When the circuit manager re-establishes a connection, the application
   exchanges full routing information with its peer.

3.5 Routing Information Flow Control

   If the circuit manager reports a circuit as down, the routing
   application is flow controlled from sending further information on
   the circuit.





Sherry & Meyer               Informational