The Nimrod Routing Architecture
RFC 1992

Document Type RFC - Informational (August 1996; No errata)
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Network Working Group                                      I. Castineyra
Request for Comments: 1992                                           BBN
Category: Informational                                       N. Chiappa
                                                           M. Steenstrup
                                                                     BBN
                                                             August 1996

                    The Nimrod Routing Architecture

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   We present a scalable internetwork routing architecture, called
   Nimrod.  The Nimrod architecture is designed to accommodate a dynamic
   internetwork of arbitrary size with heterogeneous service
   requirements and restrictions and to admit incremental deployment
   throughout an internetwork.  The key to Nimrod's scalability is its
   ability to represent and manipulate routing-related information at
   multiple levels of abstraction.

Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2. Overview of Nimrod . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1 Constraints of the Internetworking Environment  . . . . . . . 3
     2.2 The Basic Routing Functions . . . . . . . . . . . . . . . . . 5
     2.3 Scalability Features  . . . . . . . . . . . . . . . . . . . . 6
       2.3.1 Clustering and Abstraction  . . . . . . . . . . . . . . . 6
       2.3.2 Restricting Information Distribution  . . . . . . . . . . 7
       2.3.3 Local Selection of Feasible Routes  . . . . . . . . . . . 8
       2.3.4 Caching . . . . . . . . . . . . . . . . . . . . . . . . . 8
       2.3.5 Limiting Forwarding Information . . . . . . . . . . . . . 8
   3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     3.1 Endpoints   . . . . . . . . . . . . . . . . . . . . . . . . . 9
     3.2 Nodes and Adjacencies . . . . . . . . . . . . . . . . . . . . 9
     3.3 Maps  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
       3.3.1 Connectivity Specifications  . . . . . . . . . . . . . . 10
     3.4  Locators  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.5 Node Attributes  . . . . . . . . . . . . . . . . . . . . . . 11
       3.5.1 Adjacencies  . . . . . . . . . . . . . . . . . . . . . . 11
       3.5.2 Internal Maps  . . . . . . . . . . . . . . . . . . . . . 11
       3.5.3 Transit Connectivity . . . . . . . . . . . . . . . . . . 12

Castineyra, et. al.          Informational                      [Page 1]
RFC 1992              Nimrod Routing Architecture            August 1996

       3.5.4 Inbound Connectivity . . . . . . . . . . . . . . . . . . 12
       3.5.5 Outbound Connectivity  . . . . . . . . . . . . . . . . . 12
   4. Physical Realization  . . . . . . . . . . . . . . . . . . . . . 13
     4.1 Contiguity   . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.2 An Example . . . . . . . . . . . . . . . . . . . . . . . . . 14
     4.3 Multiple Locator Assignment  . . . . . . . . . . . . . . . . 15
   5. Forwarding  . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     5.1 Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.2 Trust  . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.3 Connectivity Specification (CSC) Mode  . . . . . . . . . . . 24
     5.4 Flow Mode  . . . . . . . . . . . . . . . . . . . . . . . . . 25
     5.5 Datagram Mode  . . . . . . . . . . . . . . . . . . . . . . . 25
     5.6 Connectivity Specification Sequence Mode . . . . . . . . . . 26
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 26
   7. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 26
   7. Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . 27

1. Introduction

   Nimrod is a scalable routing architecture designed to accommodate a
   continually expanding and diversifying internetwork.  First suggested
   by Noel Chiappa, the Nimrod architecture has undergone revision and
   refinement through the efforts of the Nimrod working group of the
   IETF. In this document, we present a detailed description of this
   architecture.

   The goals of Nimrod are as follows:

   1. To support a dynamic internetwork of arbitrary size by
      providing mechanisms to control the amount of routing information
      that must be known throughout an internetwork.

   2. To provide service-specific routing in the presence of multiple
      constraints imposed by service providers and users.

   3. To admit incremental deployment throughout an internetwork.

   We have designed the Nimrod architecture to meet these goals.  The
   key features of this architecture include:

   1. Representation of internetwork connectivity and services in the
      form of maps at multiple levels of abstraction.
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