Demand RIP Protocol Analysis I-D

[Gerry Meyer <[e-mail]>]

Network Working Group                                         G.M. Meyer
Internet Draft                                            Spider Systems
Expires Dec 25, 1993                                            Jun 1993


          Routing over Demand Circuits - RIP Protocol Analysis


Status of this Memo

   This memo is being distributed to members of the Internet community
   in order to solicit their reactions to the proposals contained in it.

   This document is an Internet Draft.  Internet Drafts are working
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Abstract

   As required by Routing Protocol Criteria [1], this report documents
   the key features of Routing over Demand Circuits on Wide Area
   Networks - RIP [2] and the current implementation experience.

Acknowledgements

   I would like to thank colleagues at Spider, in particular Richard
   Edmonstone and Alan Turland who developed Spider's IP RIP and IPX RIP
   and SAP implementations.












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1. Protocol Documents

   "Routing over Demand Circuits on Wide Area Networks - RIP" [2]
   suggests an enhancement to the "Routing Internet Protocol" (RIP) [3]
   and "RIP-2" [4] to allow them to run more cost-effectively on Wide
   Area Networks (WANs).

2. 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.

2.1 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.

2.2 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.









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2.3 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:

   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.

2.4 Routing Information Flow Control

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

   To prevent transmit queue overflow and also to avoid 'predictable'
   circuit down messages, the routing application can also optionally
   limit the rate of sending routing messages to an interface.

3. Implementations

   At this stage there is only believed to be one implementation.

   The Spider Systems' implementation supports all the features outlined
   for IP RIP-1, IPX RIP and IPX SAP.  RIP-2 is not currently supported.
   It has been tested against itself on X.25 and ISDN WANs.  It has also
   been tested in operation with various router and host RIP-1, IPX RIP
   and IPX SAP implementations on Ethernet LANs.

4. Security Considerations

   Security is provided through authentication of the logical and physi-
   cal address of the sender of the routing update.  Incoming call
   requests are matched by the circuit manager against a list of physi-
   cal addresses (used to make outgoing calls).  The routing application
   makes a further check against the logical address of an incoming
   update.




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   Additional security can be provided by RIP-2 authentication [2] where
   appropriate.

References


   [1]  Hinden, R., "Internet Engineering Task Force Internet Routing
        Protocol Standardization Criteria", RFC 1264, Bolt Beranek and
        Newman, Inc, October 1991.

   [2]  Meyer. G.M., "Routing over Demand Circuits on Wide Area Networks
        - RIP", Internet Draft "draft-meyer-demandrouting-01.txt",
        Spider Systems, May 1991.

   [3]  Hedrick. C., "Routing Information Protocol", RFC 1058, Rutgers
        University, June 1988.

   [4]  Malkin. G., "RIP Version 2 - Carrying Additional Information",
        RFC 1388 Draft, Xylogics, 1992.

Author's  Address:

   Gerry Meyer
   Spider Systems
   Stanwell Street
   Edinburgh EH6 5NG
   Scotland, UK

   Phone: (UK) 31 554 9424
   Fax:   (UK) 31 554 0649
   Email: [e-mail]




















Meyer                                                           [Page 4]