Protocol Analysis for Extensions to RIP to Support Demand Circuits (RFC1581)
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
As required by Routing Protocol Criteria , this report documents the key features of Routing over Demand Circuits on Wide Area Networks - RIP  and the current implementation experience.
Network Working Group G. Meyer
Request for Comments: 1581 Spider Systems
Category: Informational February 1994
Protocol Analysis for Extensions to RIP to Support Demand Circuits
Status of this Memo
This document provides information for the Internet community. This
document does not specify an Internet standard of any kind.
Distribution of this document is unlimited.
As required by Routing Protocol Criteria , this report documents
the key features of Routing over Demand Circuits on Wide Area
Networks - RIP  and the current implementation experience.
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.
1. Protocol Documents
"Extensions to RIP to Support Demand Circuits"  suggests an
enhancement to the "Routing Internet Protocol" (RIP)  and "RIP-2"
 to allow them to run more cost-effectively on Wide Area Networks
(WANs). Network management extensions for Demand RIP are described
in RIP Version 2 MIB Extensions .
Demand RIP requires that there is an underlying mechanism for
determining unreachability in a finite predictable period.
The demand extensions to RIP are particularly appropriate for WANs
where the cost - either financial or packet overhead - would make
periodic transmission of routing (or service advertising) updates
o Connection oriented Public Data Networks - for example X.25 packet
switched networks or ISDN.
o Point-to-point links supporting PPP link quality monitoring or
echo request to determine link failure.
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...