OSPF Validation
Dirk Jacob
Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 2
Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 3
SSFNet - Overview
 Simulation of very large networks
 Focus on scalability
 modeling scalability
 computing scalability
 Layered Architecture
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Scalable Simulation
 Simulator Kernel – not dedicated to simulation of networks
 „Models“ are built on top of the SSF API
 consists of only five core classes:
Entity, Event, inChannel, outChannel and process
 API hides all simulator internals
 C++ and Java bindings
 models are standard programs which extend the standard SSF classes
 Different SSF implementations available
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SSF Network Models
 Set of SSF Java models, which simulate the networking world
 distributed under the GPL
 consists of several sub-packages
Framework for protocol modeling
 SSF.Net
models for hardware components
 SSF.Util.Random
generation of multiple independent random number streams
 SSF.Util.Streams
efficient multi-point monitoring infrastructure
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 Framework for modeling of protocols
 three classes:
 ProtocolSession,
 ProtocolMessage,
 ProtocolGraph
 Packets are modeled by ProtocolMessages
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SSFNet Protocols
 SSFNet comes with a variety of protocols
 IP
 Sockets
 „Static“ OSPF
 OSPFv2
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 Models for the simulation of networking components
 Networks
 Hosts
 Routers
 Links
 Network Interfaces (NIC)
 additional Classes like packet queues, routing tables, etc.
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Modeling Topologies
 Topologies are modeled using DML
 consists of nested key/value pairs
 supports attribute substitution
 supports inheritance
 component configurations can be kept in a dictionary for reuse
 Example
dict [
myrouter [
interface [ id 0
_extends .dict.if100Mbit]
graph [
ProtocolSession[name ip
use SSF.OS.IP]
ProtocolSession[name ospf
Net [
router[ id
router[ id
.dict.myrouter ]
.dict.myrouter ]
link[ attach 1(0) attach 2(0) ]
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Role of Testing
 Protocols must be implemented correctly
 Conformance tests to prove conformance with standards
 Regression tests to verify that things still work after changes
 Testing is extremely important!
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Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 12
Categories of Testing
 Conformance testing
 Regression testing
 Performance testing
 Stress testing
 Roustness tests
 Here: focus on conformance testing
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Conformance Testing
 Verify that a protocol implementation performs as required
in the standard
 Black box testing: observe outputs, when IUT is feeded with
various inputs
 Exhaustive testing: apply every possible input sequence
 not possible with complex protocols
 Test only important input sequences
 Main problem: identify important input sequences
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OSI Testing Methodology
 Framework for conformance testing of OSI protocols
 Standardized in ISO 9646
 based on the OSI Reference Model
 Standardized test procedure
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Test Architectures
Local Method
Distributed Method
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Test Architectures (2)
Coordinated Method
Remote Method
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 standardized notation for the description of test cases
 event trees, which describe the external behavior of a protocol
 two forms: TTCN/gr and TTCN/mp
 four parts
 overview part
 declarations part
 constraints part
 dynamic part
START wait_timer
TIMEOUT wait_timer
Example for dynamic part
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Test Case Selection
 not specified in OSI framework
 but: central role for coverage and correctness of test suite
 efforts to use formal techniques
 provable correctess
 provable coverage
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Test Selection based on
 several methods for test case selection based on FSMs
 transition tours
 distinguishing sequences
 characterizing sequences (W-Method)
 unique I/O sequences
 apply an input sequence which must produce
a specific output sequence
 protocol must be specified as an FSM
 restrictions
 strongly connected
 fully specified
 not applicable to most complex protocols
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Formal Description
 data portion of protocols often are not specified as FSM
 FDTs are formal languages for specification
 Estelle
 specifications can be represented as labelled transition systems
 similar to FSMs
 different methods/algorithms for derivation of test cases from LTS
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Informal Testing
 many protocols are specified using natural language
 translating them into a FDT may cause errors
 test cases may not reflect the standard
 many formal methods cannot be applied to complex protocols
 often informal methods are used
 reading the standard and deriving tests directly
 no provable correctness and coverage
 but: „high degree of certainty“
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Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 23
OSPF Overview
 Link-state intra-domain routing protocol
 OSPF Router knows the whole topology of the network
 Specified in RFC 2328
 Routing Information is exchanged with directly attached neighors
 flooding procedure assures distribution over the whole network
 Hierarchical Concept
 support for large networks
 reduce CPU and memory requirements
 Support for multiple least cost routes to the same destination
 Uses Dijkstra‘s SPF algorithm to calculate routing tables
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OSPF Overview (2)
 Routers identify their neighbors
 Some neighbors form adjacencies in order to exchange
routing information
 Synchronization through the exchange of link state databases
 Detect link failures through periodic sending/receiving of
Hello Packets
 Changes in the topology are flooded as Link State Updates
 All information is re-flooded periodically to keep databases
 OSPF distinguishes different network types:
broadcast, nonboadcast-multiaccess (NBMA), point-to-point and point-to-multipoint
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Hierarchical Routing
 each AS can be divided into Areas
 each area has ist own Link State Database
 detailed information of area topology only known inside the area
 information about area is summarized into other areas
 special backbone area (area 0)
 all areas must be connected to the
 virtual links to connect areas
to the backbone which have no
physical connection
 Stub areas to reduce database
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Link State Database
 Contains information about area topology
 Describes a graph
 Routers and networks are vertices
 Links between vertices are edges
 Links are asociated with a cost/metric
 Network vertices are represented by a designated router
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Functional Areas
 4 mostly independent functional areas
 detection and maintenance of neighbors
 building adjacencies
 the flooding procedure
 routing table calculation
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Neighbor Discovery and
 Send Hello Packets periodically
 Include information about neighbors
 Assure bi-directional communication
 Assure that neighbors agree on certain parameters
 Elect Designated Router on broadcast and NBMA networks
 Represent the network in
the Link State Database
 reduce the number of
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Building Adjacencies
 neighbors with bi-directional communication become adjacent
 dependent of network type
 Synchronization of Link State Databases
 Negotiate, who is the master in this process
 Master controls the exchange process
 Send summary of own Database in Database Description Packets
 Request unknown or more recent LSAs from the neighbor
 Send requested LSAs to the neighbor
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Reliable Flooding
 Each router must keep synchronized with every other router in
the same area
 Udates are flooded to all adjacent neighbors
 Every Update must be acknowledged
 Explicitly through an Ack packet
 Implicitly with an Update of the same LSA flooded back
 Retransmit Update if there is no such acknowledgement
 Possibility of delayed Acks to minimize number of packets
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Link State Advertisements
 different types of LSAs
 Router LSAs – represent a router with all its associated links
 Network LSAs – represent broadcast and NBMA networks
 Network Summary LSAs – represent routes to destinations in other areas
 ASBR Summary LSAs – represent routes to AS boundary routers
 AS-external LSAs – represent routes to AS external destinations
 LSAs have an age associated with them
 aging in databases and during the flooding procedure
 premature aging to remove LSAs from databases
 don‘t use LSAs that are older than 1 hour for routing calculation
 refresh own LSAs that are older than ½ hour
 use of sequence numbers to determine, which instance of an
LSA is the most recent one
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Routing Table Calculation
 Dijkstra‘s Shortest Path First algorithm
 Calculate SPF tree for the area using the SPF algorithm
 Consider only routers and network nodes from the LSDB
 Add stub networks to the tree
 Add inter-area routes to the tree
 Examine summary LSAs to find better routes for destinations
in areas connected through virtual links
 Add AS external routes to the tree
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Testing OSPF
 take advantage from the functional structure
 four smaller testing problems instead of a big one
 each functional area can be tested independently
 take care of dependencies
 functional hierarchy rather than completely independent
 test „lower level“ functionality first
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Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 35
OSPF Test Suites
 most of the formal methods require protocol specification
with FSMs
 OSPF only partially specified by FSMs
 many parts like LSA origination not covered
 most parts are specified using natural language
 OSPF consists of multiple concurrent processes
 Formal methods require formal specifications
 not provided for OSPF, must be derived manually from standard
 Formal methods difficult to apply to OSPF
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C-TTCN Based Test Suite
 approach to testing OSPF with formal methods
 modeling test cases with C-TTCN
 extension to TTCN which allows modeling of concurrent behaviors
 OSPF specification was translated into a FDT called CEBE
 based on LTS, which are similar to FSMs
 resulting test suite had over 4000 test cases
 after elimination of unimportant test cases: 543 test cases
 Problem: how to prove that formal specification covers the
complete OSPF specification?
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IOL Test Suite
 IOL is a test lab, whose services are used by many vendors
 Test suites are derived by „carefully reading the standards“
 good coverage and correctness
 used by many vendors
 refined over the time
 covers the functional areas of OSPF presented before
 Hello Protocol tests
 Fooding and Adjacency tests
 Link state advertisement tests
 Route calculation tests
 Additionally: Configuration and Formatting tests
 78 test cases with several test steps each
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Commecial Test Products
 software solution for conformance and performance testing
 used by many well-known vendors
 provides automated testing
 OSPF test suite consists of over 300 test cases from 12 groups
 no formal methods are used
 QARobot / RouterTester
 hardware solution together with protocol and test suite software
 conformance and stress testing
 OSPF test sute has 70 test cases from 12 groups
 no formal methods are used
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Testing OSPF in Practice
 in practice: mixture of several different test products and/or
lab testing
 Example: ZebOS Advanced Routing Suite
 basic testing with ANVL
 additionally performance testing using other test tools
 after that: lab testing at the IOL and other labs
 Testing against multiple test suites increases probability of
finding any offences against the specification
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Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 41
OSPF Test Suite for SSFNet
 OSI methods can be easily transferred into SSFNet
 Test Procedure needs not to be modified
 Extended test architecture to support distributed test behavior
 Test cases can be modeled using appropriate DML scenarios
 some test cases need implementation of specialized testers
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 Goal: implement a complete OSPF for SSFNet
 Must correctly implement the standard
 until now:
 Hello Protocol, Database Exchange, Flooding and Routing Table Calculation
 only Router LSAs
 restricted to point-to-point networks
 no vitual links or authentication
 work still in progress
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Test Selection
 depends on several criteria
 correctness
 coverage
 relevance and acceptance in practice
 ease of implementation
 applicability early during development
 availability
 formal methods are difficult to apply and not very common
 dedicated test equipment not applicable easily
 software solution like ANVL also not applicable
 IOL test suite seems the best choice
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Design of the Test Suite
 many tests can be implemented using standard OSPF behavior
 some require specialized testers with non-standard behavior
 topology changes such as link failures
 simple errors like malformed packets
 complex tests which are aware of the state
 test behaviors are implemented in SSF.OS.OSPFv2.test
 five subsidiary test suites (see IOL test suite)
 additionally: tests for packet forwarding and equal-cost multipath
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Design of the Test Suite (2)
 each test is performed in several steps
 simulation of the scenario
 evaluation of the logs
 assignment of a verdict
 evaluation is done automatically by PERL scripts
 test suite passes only when all tests pass
 common components for simulation are kept in a test suite
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 contains classes to implement test behavior
 Configurator
 Reset
 UnreliableIP
 IPwithErrorInjection
 PacketGenerator
 OSPFMonitor, OSPFDumpPro
 main task: manipulate packets coming from or sent to OSPF
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SSF.OS.OSPFv2.test (2)
 class hierarchy to be able to use different classes of testers
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Implementation of Test
 model test setup in DML
 replace broadcast networks by a set of point-to-point links
 features specific to broadcast networks, virtual links, etc.
not yet tested
 use tester classes to model tester behavior whenever necessary
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Example: old_lsa_rcpt
• a router must discard an LSA
that is older than the copy in ist
own database
• routers synchronize their databases
• then the tester sends a new LSA with sequence no. 0x70000001
• after that, it sends another LSA with sequence no. 0x 8FFFFFFE
• IUT must send back the newer instance and discard
the second LSA
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Additional Tests
 operation of the SPF algorithm not tested by IOL test suite
 packet forwarding and support of equal-cost multiplath not
tested in IOL test suite
 provide additional test scenarios for these features
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Test Results
 most tests PASSED
 some of the tests FAILED because of features missing from
SSFnet (esp. multicast support)
 many tests INCONCLUSIVE, because features are not yet
 tests were very valuable during development
 helped identifying problems early
 helped make code more stable
 helped to find even „standard bugs“ like NullPointerExceptions
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Conformance Testing
OSPF Test Suites
Implementation for SSFNet
Dirk Jacob, Page 53
 goals:
 find out how to test protocols
 provide SSFNet with a test suite for OSPF
 formal methods seem not suitale for practical testing
 informal methods sufficient when used carefully
 formal methods could have grater impact if test suites were provided with
the protocol standards
 testing is extremely important and useful
 to prove cnformance to the standard (at least to some degree)
 to find bugs in the implementation
 to understand, what a protocol really should do
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 OSPF validation in SSFNet:
 http://ssfnet.d-jacob.net
 SSFNet Website:
 http://www.ssfnet.org
 Test equipment and test suites:
 http://www.agilent.com
 http://www.ixia.com
 http://www.iol.unh.edu
 ... or send me a mail:
 dirk@d-jacob.net
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Dirk Jacob, Page 56

OSPF Validation