Introduction to OSPF dynamic routing protocol consistency test

I. Introduction

With the development of computer networks and communication technologies, especially the interconnection of open heterogeneous networks, protocol design and implementation become more and more complex, and the theory and technology of protocol testing have been developed accordingly. Protocol testing includes four types of tests: consistency testing, interoperability testing, performance testing, and robustness testing. The protocol consistency test mainly verifies the accuracy of the Protocol Implementation of Network products and determines whether the Protocol Implementation of Network products meets the international standards of the Protocol, to ensure that the various implementation versions of the Protocol can communicate with each other and communicate reliably. Therefore, consistency testing is the most basic content of protocol testing and the basis of the other three tests.

Nowadays, the TCP/IP-based Internet network has become the basis for global information development and communication. It uses vrouters as the basic exchange node and various local area/WAN as the media. Most of the intra-Domain Routing Protocols in a WAN Use OSPF to forward route information, and OSPF is mainly located on the intra-domain routers. It is the core protocol of the existing TCP/IP network relay system. This article introduces the protocol consistency testing principle and abstract testing method, focuses on the OSPF protocol consistency testing technology, and discusses the design of the OSPF protocol test set.

Ii. protocol consistency test

1. consistency testing principle

ISO/IEC9646 provides the basic methods and framework for protocol consistency, develops the design steps and description methods for the test set, and provides guidance for the implementation of the test system.

In essence, protocol consistency testing uses a set of test sequences to perform a black box test on the tested IUT in a certain network environment. By comparing the similarities and differences between the actual output and the expected output of IUT, determine the extent to which IUT is consistent with the Protocol description, and establish the level of power that IUT passes the consistency test when it is interconnected. For the process and principle of consistency testing, see Figure 1. In Figure 1, PICSProtocol Implementation Conformance Statement is a description of protocol Implementation consistency, indicating Implementation requirements, capabilities, and options; PIXITProtocol Implementation Extra Information for Testing) Additional Information for protocol Implementation, provide the protocol parameters that must be specified during the test. The procedure is as follows:

1) iut pics analysis: Performs static consistency SCR checks on IUT, and analyzes whether the PICS are consistent with the SCR specified by relevant standards.

2) define the purpose of testing according to the specifications, use the information provided by PIXIT and the quantitative test examples of the consistency test combination, write the Abstract Test Set ATS, and then parameterize the ATS to generate the executable Test Set ETS.

3) Use ETS to automatically perform IUT consistency tests to form detailed test reports.

4) IUT final consistency test, which combines known PICS and PIXIT analysis with test results, obtains IUT consensus conclusions on standard requirements, and records them in the consistency test report.

2. Abstract Test Method for consistency testing

The consistency test model uses the service primitive ASP and protocol data unit PDU to control and observe the output and input from the tested implementation at the control and observation points. Generally, the tested systems are divided into two categories: End Systems and relay systems. In ISO/IEC9646, different abstract testing methods are defined for the consistency tests of these two types of systems.

According to the locations and functions of UT and LT in the consistency tester, there are four types of abstract consistency testing methods for the end system: local testing, distribution testing, coordination testing, and remote testing. The local test method can be directly observed and controlled on the IUT upper and lower interfaces in the tested system. The other three are external test methods. The distribution test method requires that an UT provides ASP for this interface. The Coordination test method does not require upper-layer external interfaces. The standard test management protocol TMP and the lower tester are used for test management and coordination. There is no dedicated tester in the remote test method, and some tester functions are implemented by the tested system. However, the lower Tester of the three testing methods is to control and observe IUT through the Protocol Data Unit PDU transmitted on the communication link.

There are two Abstract Test Methods for consistency tests on the relay systems of two sub-networks: loop test and cross-sectional test. The loop-back test method performs the loop connection on the port of the relay system. This loop can be completed in the relay system or in the second subnet. There are two observation and control points on the other subnet of SAP at the Business Access Point of the relay system, so only one tester is needed. The test function of the loop test method is too simple and therefore not practical. The cross-sectional test method has an observation and control point on each of the two sub-networks connected to the business. Two testers are required, which makes it difficult to synchronize the two testers.

Iii. OSPF protocol

1. OSPF protocol features

OSPF is a link status protocol based on the Djkstra algorithm. It is used for routing selection in autonomous systems. The OSPF protocol has the following features:

● When the network extension changes rapidly, the network overhead caused by the Protocol is very small;

● Server Load balancer is supported. Multiple Routes of the same destination can be retained;

● Loop generation is not easy;

● Authenticate route update information to ensure its validity;

● Supports the division of regions, supports large-scale networks, and has high scalability.

The OSPF protocol supports three types of network connections:

● Point-to-point connections between two routers;

● LAN with broadcast function;

● Wide area networks without broadcast functions.

2. OSPF protocol Principle

The content of the OSPF routing protocol can be divided into three parts: the exchange and diffusion protocol, the maintenance of the network topology database content, and the calculation of the route table. The Exchange Protocol establishes an adjacent router and synchronizes each piece of content in the network topology database with adjacent nodes through the diffusion protocol, in this way, the network topology database maintained by each node in the entire network is synchronized. When the network topology is changed, each node recalculates the entire or part of the route table to quickly update the route, so that the changes in the network topology are promptly reflected in the corresponding routing table.

3. There are five types of OSPF packets.

● Hello message: Used to discover and maintain the accessibility of neighboring stations;

● Database Description message: Provides the abstract information of the link status to the neighboring station;

● Link State Request message: sends detailed information about certain Link states to the Request from the other party;

● Link State Update message: Update the Link State to the entire network using the diffusion method;

● Link State Acknowledgment message: confirms the Link update message.

Iv. methods for testing OSPF protocol consistency

OSPF protocol is the routing protocol used in the domain. Therefore, the cross-section test method is used for OSPF protocol consistency testing. In the cross-sectional test method, PCO1 and PCO2 are generally integrated into a tester to make the two PCO of two subnets easy to synchronize.

The editor can be a TTCN editor recommended by ISO9646 or an editor in other languages. First, compile the Abstract Test Set ATS in the editor. ATS is output in MP format of fixed grammar text files, similar to assembly language or advanced language source program. Then, the MP file is compiled into an executable file ETS by the editor. The processor is a key engine for testing and execution. It interprets and executes ETS, the test set selected by PICS and PIXIT, and processes the PDU, the Protocol Data Unit transmitted by PCO1 or PCO2, control the test process based on the content of the test set. All the information required to generate the test report. In this test structure, the two IUT ports correspond to PCO. When the processor sends an OSPF Packet from PCO1 to the SUT, the packet is routed through the OSPF module, OSPF packets are forwarded from subnet 1 to subnet 2, and the processor obtains data packets from PCO2 in subnet 2. Since both PCO1 and PCO2 are integrated into the tester, two LT coordination processes can be easily controlled.

V. Design of OSPF Test Set

The test set is the basis for protocol consistency testing. It defines the behavior of the test system and protocol entity in detail in the form of the most basic test event sequence, in this way, the test passes or fails. the test set has the following hierarchies: Test Set → test group → test example → test step → Test Event. The test set can be described using the TTCN formal language.

Compared with the OSI protocol, the OSPF protocol has simple behavior, and there is no Packet Exchange between the peer entities for link building or traffic control. Based on the recommendations of ISO/IEC9646, we analyze the protocol description and synthesize the conditions to generate the testing purpose, design and generate the OSPF protocol test set, and compile the OSPF protocol test specification. The resulting OSPF test set consists of five test groups. A total of 69 test cases are shown in Table 1 ).

Table 1 OSPF Test Set

These test group examples cover the main functions in the OSPF protocol description, with good completeness.

Vi. test applications

According to the test method and structure discussed in this article, the test tool uses the QA Robot Tester of Agilent to test the OSPF protocol consistency. You can also use the TTCN-based PITS testing system developed by Tsinghua University. The QARobot tester generates ETS using the QBOL language and compiles ETS using the QBOL editor. It uses a UNIX operating system internally and provides visualized interface operations.

We participated in the testing of the core vro of the national "863" Broadband Information Demonstration network. The consistency test of OSPF protocol is carried out on the core routers developed by ZTE, julong and Datang respectively using the QARobot tester. After each router passes the OSPF protocol consistency test, the functions and performance of the OSPF module have been significantly improved, and the pass rate of the test instance has increased from 50% to nearly 90%.

It has been proved through practice that consistency testing is a good method to detect and locate errors while providing correction suggestions during protocol software design and development.
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