RFC 1581 (rfc1581) - Page 2 of 4

Protocol Analysis for Extensions to RIP to Support Demand Circuits

RFC 1581                       Demand RIP                  February 1994


   A demand RIP implementation runs standard RIP on Local Area Networks
   (LANs) allowing them to interoperate transparently with
   implementations adhering to the original specifications.

3. Key Features

   The proposal shares the same basic algorithms as RIP or RIP-2 when
   running on LANs or fixed point-to-point links; Packet formats,
   broadcast frequency, triggered update operation and database timeouts
   are all unmodified.

   The new features operate on WANs which use switched circuits on
   demand to achieve intermittent connectivity.  Instead of using
   periodic 'broadcasts', information is only sent as triggered updates.
   The proposal makes use of features of the underlying connection
   oriented service to provide feedback on connectivity.

3.1 Triggered Updates

   Updates are only sent on the WAN when an event changes the routing
   database.  Each update is retransmitted until acknowledged.
   Information received in an update is not timed out.

   The packet format of a RIP response is modified (with a different
   unique command field) to include sequence and fragment number
   information.  An acknowledgement packet is also defined.

3.2 Circuit Manager

   The circuit manager running below the IP network layer is responsible
   for establishing a circuit to the next hop router whenever there is
   data (or a routing update) to transfer.  After a period of inactivity
   the circuit will be closed by the circuit manager.

   If the circuit manager fails to make a connection a circuit down
   indication is sent to the routing application.  The circuit manager
   will then attempt at (increasing) intervals to establish a
   connection.  When successful a circuit up indication is sent to the
   routing application.

3.3 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:






Meyer