📄 rfc995.txt
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Network Working Group ANSI X3S3.3 86-118
Request for Comments: 995 ISO TC97/SC6/N 4053
April 1986
I S O
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
______________________________________________________________________
| |
| ISO/TC 97/SC 6 |
| TELECOMMUNICATIONS AND INFORMATION |
| EXCHANGE BETWEEN SYSTEMS |
| Secretariat: USA (ANSI) |
| |
| |
|_____________________________________________________________________|
Title: End System to Intermediate System Routing Exchange Protocol
for use in conjunction with ISO 8473
Source: SC6/WG2
Project 97.6.41
___________________________________________________________________________
|This document is a progression of SC6/N3862, edited to incorporate member |
|body comments and discussion at the Florence meeting of SC6/WG2. Pursuant |
|to Recommendation 5 of that meeting, comments from member bodies on this |
|revision text are requested for discussion at the Tokyo meeting of SC6 |
|and WGs. |
|__________________________________________________________________________|
ISO N4053 [Page 1]
RFC 995 December 1986
Contents
1 Introduction 5
2 Scope and Field of Application 6
3 References 7
SECTION ONE. GENERAL 9
4 Definitions 9
4.1 Reference Model Definitions . . . . . . . . . . . . . . . . . 9
4.2 Network Layer Architecture Definitions . . . . . . . . . . . 9
4.3 Network Layer Addressing Definitions . . . . . . . . . . . . 9
4.4 Local Area Network Definitions . . . . . . . . . . . . . . . 10
4.5 Additional Definitions . . . . . . . . . . . . . . . . . . . . 10
5 Symbols and Abbreviations 10
5.1 Data Units . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2 Protocol Data Units . . . . . . . . . . . . . . . . . . . . . 10
5.3 Protocol Data Unit Fields . . . . . . . . . . . . . . . . . . 10
5.4 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.5 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . 11
6 Overview of the Protocol 11
6.1 Information Provided by the Protocol . . . . . . . . . . . . . 11
6.2 Subsets of the Protocol. . . . . . . . . . . . . . . . . . . . 12
6.3 Addressing . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4 Underlying Service Assumed by the Protocol . . . . . . . . . 12
6.4.1 Subnetwork Addresses . . . . . . . . . . . . . . . . . 12
6.4.2 Subnetwork User Data . . . . . . . . . . . . . . . . . 13
6.5 Service Assumed from Local Environment . . . . . . . . . . . . 13
6.6 Subnetwork Types . . . . . . . . . . . . . . . . . . . . . . . 14
6.6.1 Point-to-Point Subnetworks . . . . . . . . . . . . . . 15
6.6.2 Broadcast Subnetworks . . . . . . . . . . . . . . . . 15
6.6.3 General Topology Subnetworks . . . . . . . . . . . . . 16
SECTION TWO. SPECIFICATION OF THE PROTOCOL 18
7 Protocol Functions 18
7.1 Protocol Timers . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.1 Configuration Timer . . . . . . . . . . . . . . . . . 18
7.1.2 Holding Timer . . . . . . . . . . . . . . . . . . . . 18
7.2 Report Configuration Function . . . . . . . . . . . . . . . . 18
7.2.1 Report Configuration by End Systems . . . . . . . . . 19
7.2.2 Report Configuration by Intermediate Systems . . . . . 19
7.3 Record Configuration Function . . . . . . . . . . . . . . . . 20
7.4 Flush Old Configuration Function . . . . . . . . . . . . . . 20
7.5 Query Configuration Function . . . . . . . . . . . . . . . . . 20
ISO N4053 [Page 2]
RFC 995 December 1986
7.6 Configuration Response Function . . . . . . . . . . . . . . . 21
7.7 Request Redirect Function. . . . . . . . . . . . . . . . . . . 22
7.8 Record Redirect Function . . . . . . . . . . . . . . . . . . . 23
7.9 Refresh Redirect Function . . . . . . . . . . . . . . . . . . 23
7.10 Flush Old Redirect Function . . . . . . . . . . . . . . . . . 24
7.11 PDU Header Error Detection . . . . . . . . . . . . . . . . . 24
7.12 Classification of Functions . . . . . . . . . . . . . . . . . 25
8 Structure and Encoding of PDUs 25
8.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.2 Fixed Part . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.2.1 General . . . . . . . . . . . . . . . . . . . . . . . 26
8.2.2 Network Layer Protocol Identifier . . . . . . . . . . 27
8.2.3 Length Indicator . . . . . . . . . . . . . . . . . . . 27
8.2.4 Version/Protocol Identifier Extension . . . . . . . . 27
8.2.5 Type Code . . . . . . . . . . . . . . . . . . . . . . 28
8.2.6 Holding Time . . . . . . . . . . . . . . . . . . . . . 28
8.2.7 PDU Checksum . . . . . . . . . . . . . . . . . . . . . 28
8.3 Network Address Part . . . . . . . . . . . . . . . . . . . . . 28
8.3.1 General . . . . . . . . . . . . . . . . . . . . . . . 28
8.3.2 NPAI (Network Protocol Address Information) En-
coding . . . . . . . . . . . . . . . . . . . . . . . . 28
8.3.3 Source Address Parameter for ESH PDU . . . . . . . . 29
8.3.4 Network Entity Title Parameter for ISH PDU . . . . . . 29
8.3.5 Destination Address Parameter for RD PDU . . . . . . . 30
8.4 Subnetwork Address Part . . . . . . . . . . . . . . . . . . . 30
8.4.1 Subnetwork Address Parameter for RD PDU . . . . . . . 31
8.5 Options Part . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.5.1 General . . . . . . . . . . . . . . . . . . . . . . . 31
8.5.2 Security . . . . . . . . . . . . . . . . . . . . . . . 32
8.5.3 Quality of Service Maintenance . . . . . . . . . . . . 33
8.5.4 Priority . . . . . . . . . . . . . . . . . . . . . . . 33
8.6 End System Hello (ESH) PDU . . . . . . . . . . . . . . . . . . 34
8.6.1 Structure . . . . . . . . . . . . . . . . . . . . . . 34
8.7 Intermediate System Hello (ISH) PDU . . . . . . . . . . . . . 35
8.7.1 Structure . . . . . . . . . . . . . . . . . . . . . . 35
8.8 Redirect (RD) PDU. . . . . . . . . . . . . . . . . . . . . . . 36
8.8.1 Structure . . . . . . . . . . . . . . . . . . . . . . 36
9 Formal Description 37
10 Conformance 37
ANNEX A. SUPPORTING TECHNICAL MATERIAL 38
A.1 Use of Timers . . . . . . . . . . . . . . . . . . . . . . . . 38
A.1.1 Example of Holding Time for Route Redirection . . . . 38
A.1.2 Example of Holding Timer for Configuration Informa-
tion . . . . . . . . . . . . . . . . . . . . . . . . . 39
A.2 Refresh and timeout of Redirection information . . . . . . . . 39
A.3 System Initialization Considerations . . . . . . . . . . . . . 40
A.4 Optimizations for Flushing Redirects . . . . . . . . . . . . 41
ISO N4053 [Page 3]
RFC 995 December 1986
List of Tables
1 Service Primitives for Underlying Service . . . . . . . . . . 12
2 Timer Primitives . . . . . . . . . . . . . . . . . . . . . . . 14
3 Categories of Protocol Functions . . . . . . . . . . . . . . . 25
4 Valid PDU Types . . . . . . . . . . . . . . . . . . . . . . . 28
List of Figures
1 PDU Header -- Fixed Part . . . . . . . . . . . . . . . . . . . 27
2 Address Parameters . . . . . . . . . . . . . . . . . . . . . 29
3 ESH PDU - Network Address Part . . . . . . . . . . . . . . . 29
4 ISH PDU - Network Address Part . . . . . . . . . . . . . . . . 30
5 RD PDU - Network Address Part . . . . . . . . . . . . . . . . 30
6 ESH PDU - Address Part . . . . . . . . . . . . . . . . . . . 31
7 All PDUs - Options Part . . . . . . . . . . . . . . . . . . . 31
8 Encoding of Option Parameters . . . . . . . . . . . . . . . . 32
9 ESH PDU Format . . . . . . . . . . . . . . . . . . . . . . . . 34
10 ISH PDU Format . . . . . . . . . . . . . . . . . . . . . . . . 35
11 RD PDU Format when Redirect is to an IS . . . . . . . . . . . 36
12 RD PDU Format when Redirect is to an ES . . . . . . . . . . . 37
ISO N4053 [Page 4]
RFC 995 December 1986
1 Introduction
This Protocol is one of a set of International Standards produced to
facilitate the interconnection of open systems. The set of standards
covers the services and protocols required to achieve such intercon-
nection.
This Protocol is positioned with respect to other related standards
by the layers defined in the Reference Model for Open System Inter-
connection (ISO 7498) and by the structure defined in the Internal
Organization of the Network Layer (DIS 8648). In particular, it is a
protocol of the Network Layer. This protocol permits End Systems and
Intermediate Systems to exchange configuration and routing informa-
tion to facilitate the operation of the routing and relaying func-
tions of the Network Layer.
The aspects of Network Layer routing that are concerned with communi-
cation between end systems and intermediate systems on the same sub-
network are to a great extent separable from the aspects that are
concerned with communication among the intermediate systems that con-
nect multiple subnetworks. This protocol addresses only the former
aspects. It will be significantly enhanced by the cooperative opera-
tion of an additional protocol that provides for the exchange of
routing information among intermediate systems, but is useful whether
or not such an additional protocol is available.
This protocol provides solutions for the following practical problems:
1. How do end systems discover the existence and reachability of
intermediate systems that can route NPDUs to destinations on
subnetworks other than the one(s) to which the end system is
directly connected?
2. How do end systems discover the existence and reachability of
other end systems on the same subnetwork (when direct
examination of the destination NSAP address does not provide
information about the destination subnetwork)?
3. How do intermediate systems discover the existence and
reachability of end systems on each of the subnetworks to
which they are directly connected?
4. How do end systems decide which intermediate system to use
to forward NPDUs to a particular destination when more than one
intermediate system is accessible?
The protocol assumes that:
1. Routing to a specified subnetwork point of attachment address
(SNPA) on the same subnetwork is carried out satisfactorily by
the subnetwork itself.
ISO N4053 [Page 5]
RFC 995 December 1986
2. The subnetwork is not, however, capable of routing on a global
basis using the NSAP address alone to achieve communication
with a requested destination.
Note:
Consequently, it is not possible to use Application Layer
communication to carry out the functions of this protocol.
The protocol is connectionless, and is designed to:
1. minimize the amount of a priori state information needed by
end systems before they can begin to communicate with other
end systems;
2. minimize the amount of memory needed to store routing
information in end systems; and
3. minimize the computational complexity of end system routing
algorithms.
The protocol is also designed to operate in close conjunction with
the Protocol for the Provision of the Connectionless-mode Network
Service (ISO 8473). Since routing styles are usually closely related
to communication styles, the information that this protocol provides
to end systems and intermediate systems may or may not be appropriate
information for supporting routing functions when a Network Layer
protocol other than ISO 8473 is used.
2 Scope and Field of Application
This International Standard specifies a protocol which is used by
Network Layer entities operating ISO 8473 in End Systems and Inter-
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