Network Working Group G. Meyer
Request for Comments: 1582 Spider Systems
Category: Standards Track February 1994
Extensions to RIP to Support Demand Circuits
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Running routing protocols on connection oriented Public Data
Networks, for example X.25 packet switched networks or ISDN, can be
eXPensive if the standard form of periodic broadcasting of routing
information is adhered to. The high cost arises because a connection
has to all practical intents and purposes be kept open to every
destination to which routing information is to be sent, whether or
not it is being used to carry user data.
Routing information may also fail to be propagated if the number of
destinations to which the routing information is to be sent exceeds
the number of channels available to the router on the Wide Area
Network (WAN).
This memo defines a generalized modification which can be applied to
Bellman-Ford (or distance vector) algorithm information broadcasting
protocols, for example IP RIP, Netware RIP or Netware SAP, which
overcomes the limitations of the traditional methods described above.
The routing protocols support a purely triggered update mechanism on
demand circuits on WANs. The protocols run UNMODIFIED on LANs or
fixed point-to-point links.
Routing information is sent on the WAN when the routing database is
modified by new routing information received from another interface.
When this happens a (triggered) update is sent to a list of
destinations on other WAN interfaces. Because routing protocols are
datagram based they are not guaranteed to be received by the peer
router on the WAN. An acknowledgement and retransmission mechanism
is provided to ensure that routing updates are received.
The WAN circuit manager advises the routing applications on the
reachability and non-reachability of destinations on the WAN.
Acknowledgements
I would like to thank colleagues at Spider, in particular Richard
Edmonstone, Tom Daniel and Alam Turland, Yakov Rekhter (IBM), Martha
Steenstrup (BBN), and members of the RIP-2 working group of the IETF
for stimulating discussions and comments which helped to clarify this
memo.
Conventions
The following language conventions are used in the items of
specification in this document:
o MUST -- the item is an absolute requirement of the specification.
MUST is only used where it is actually required for interoperation,
not to try to impose a particular method on implementors
where not required for interoperability.
o SHOULD -- the item should be followed for all but exceptional cir-
cumstances.
o MAY or optional -- the item is truly optional and may be followed
or ignored according to the needs of the implementor.
The Words "should" and "may" are also used, in lower case, in their
more ordinary senses.
Table of Contents
1. IntrodUCtion ........................................... 3
2. Running a routing Protocol on the WAN .................. 4
2.1. Overview ......................................... 4
2.2. Presumption of Reachability ...................... 6
2.3. WAN Router list .................................. 7
2.4. Triggered Updates and Unreliable Delivery ........ 8
2.5. Guaranteeing delivery of Routing Updates ......... 8
2.6. The Routing Database ............................. 9
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