© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 4 Lesson 1 1 The IS-IS Protocol BSCI Module 4 Lesson 1 Introducing IS-IS and Integrated IS-IS Routing

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 2 BSCI Module 4 Lesson 1 Objectives  Describe IS-IS routing and some of the ways in which IS-IS is used  Describe the features of integrated IS-IS routing  Explain the principles and issues of integrated IS-IS design  Describe the features of the ES-IS protocol  Describe how to differentiate among the four OSI routing levels  Explain the similarities and differences between IS-IS and OSPF

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 3 BSCI Module 4 Lesson 1 Purpose of this Lesson  Coverage of topics new to the “Introducing IS-IS and Integrated IS-IS Routing” section in the “IS-IS” module of BSCI.  What’s new in this module? Describe the features of the ES-IS protocol Explain the similarities and differences between IS-IS and OSPF

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 4 BSCI Module 4 Lesson 1 Uses for IS-IS Routing Large ISPs  Stable protocol  Originally deployed by ISPs because US government mandated internet support of OSI and IP

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 5 BSCI Module 4 Lesson 1 IS-IS Routing  IS = router  IS-IS was originally designed as the IGP for the Connectionless Network Service (CLNS), part of the OSI protocol suite.  The OSI protocol suite layer 3 protocol is the Connectionless Network Protocol (CLNP).  IS-IS uses CLNS addresses to identify routers and build the LSDB.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 6 BSCI Module 4 Lesson 1 IS-IS Features  Link-state routing protocol  Supports VLSM  Uses Dijkstra’s SPF algorithm; has fast convergence  Uses Hellos to establish adjacencies and LSPs to exchange link-state information  Efficient use of bandwidth, memory, and processor  Supports two routing levels: Level 1: Builds common topology of system IDs in local area and routes within area using lowest cost path. Level 2: Exchanges prefix information (area addresses) between areas. Routes traffic to area using lowest-cost path.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 7 BSCI Module 4 Lesson 1 IS-IS Link-State Operation Routers identified as Level 1, Level 2, or Level 1-2:  Level 1 routers use LSPs to build topology for local area.  Level 2 routers use LSPs to build topology between different areas.  Level 1-2 routers act as border routers between Level 1 and Level 2 routing domains.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 8 BSCI Module 4 Lesson 1 Integrated IS-IS Routing  Integrated IS-IS is IS-IS for multiple protocols: For IP, CLNS, or both  Uses its own PDUs to transport IP routing information; updates are not sent in IP packets.  Requires CLNS addresses, even if only routing for IP.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 9 BSCI Module 4 Lesson 1 Integrated IS-IS Design Principles  IP and CLNP addresses must be planned.  Use two-level hierarchy for scalability: Limits LSP flooding Provides opportunity for summarization  Summarization: Limits update traffic Minimizes router memory and CPU usages

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 10 BSCI Module 4 Lesson 1 Issues with Integrated IS-IS  Default narrow metrics are limited to 6-bit interface and 10-bit path metric: In Cisco IOS 12.0, wide metrics allow 24-bit interface and 32- bit path metric.  Cisco IOS software has default metric of 10 on all interfaces.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 11 BSCI Module 4 Lesson 1 End System-to-Intermediate System  ES-IS forms adjacencies between ESs and routers (ISs). IP end-systems don’t use ES-IS  ESs transmit ESHs to announce their presence to ISs.  ISs transmit ISHs to announce their presence to ESs.  ISs transmit IIHs to other ISs.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 12 BSCI Module 4 Lesson 1 Four OSI Routing Levels

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 13 BSCI Module 4 Lesson 1 Similarities Between IS-IS and OSPF  Integrated IS-IS and OSPF are both open standard link- state protocols with the following similar features: Link-state representation, aging timers, and LSDB synchronization SPF algorithms Update, decision, and flooding processes VLSM support  Scalability of link-state protocols has been proven (used in ISP backbones).  They both converge quickly after changes.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 14 BSCI Module 4 Lesson 1 Integrated IS-IS vs. OSPF: Area Design  OSPF is based on a central backbone with all areas attached to it. In OSPF the border is inside routers (ABRs) Each link belongs to one area

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 15 BSCI Module 4 Lesson 1 Advantages of Integrated IS-IS  Supports CLNP and IP  More extensible through Type, Length, Value (TLV) design

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 16 BSCI Module 4 Lesson 1 Advantages of OSPF  OSPF has more features, including: Has three area types: normal, stub, and NSSA Defaults to scaled metric (IS-IS always 10)  OSPF is supported by many vendors.  Information, examples, and experienced engineers are easier to find.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 17 BSCI Module 4 Lesson 1 Comparison of Integrated IS-IS and OSPF OSPFIntegrated IS-IS Area border inside routers (ABRs)Area border on links Each link in only 1 areaEach router in only 1 area More complex to extend backboneSimple extension of backbone Many small LSAs sentFewer LSPs sent Runs on top of IPRuns on top of data-link layer Requires IP addressesRequires IP and CLNS addresses Default metric is scaled by interface bandwidth Default metric is 10 for all interfaces Not easy to extendEasy to support new protocols with new TLV tuples Equipment, personnel, and information more readily available Equipment, personnel, and information not as easily available The following table summarizes the differences between OSPF and integrated IS-IS.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 18 BSCI Module 4 Lesson 1 Summary.  IS-IS is a popular routing protocol in the ISP industry.  IS-IS is a stable, fast converging IGP that is positioned to route IPv4, CLNS, or IPv6.  All IS-IS interfaces have a default metric of 10.  ES-IS (for CLNS routing only) provides discovery between host and routers using hello packets to form adjacencies. Hosts send ESHs, while routers send ISHs.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 19 BSCI Module 4 Lesson 1 Summary (Cont.).  OSI defines routing levels 0 through 3. Level 0 is between ES and IS. Levels 1 and 2 are between IS and IS to support intradomain routing. Level 3 supports interdomain routing. Level 1 is intra-area; Level 2 is interarea.  IS-IS and OSPF are both open standard link state routing protocols that support VLSM, scalability, and quick convergence.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 20 BSCI Module 4 Lesson 1 Activity  List all of the features of both IS-IS and OSPF and compare the advantages and disadvantages of both.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 21 BSCI Module 4 Lesson 1 Self Check  How many levels are supported by IS-IS and ES-IS?  Which routing protocol is most closely related to IS-IS?  What is the default metric for IS-IS?  What are advantages of using IS-IS?

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 22 BSCI Module 4 Lesson 1 Additional Links  wrel/ps1835/products_configuration_guide_chapter091 86a00800c5bc1.html wrel/ps1835/products_configuration_guide_chapter091 86a00800c5bc1.html  -ISIS-WP2-F02_BIF.html -ISIS-WP2-F02_BIF.html  re/ios122/122cgcr/fipr_c/ipcprt2/1cfisis.htm re/ios122/122cgcr/fipr_c/ipcprt2/1cfisis.htm.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 23 BSCI Module 4 Lesson 1 Q and A

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 24 BSCI Module 4 Lesson 1