The is is protocol
This presentation is the property of its rightful owner.
Sponsored Links
1 / 24

The IS-IS Protocol PowerPoint PPT Presentation


  • 113 Views
  • Uploaded on
  • Presentation posted in: General

The IS-IS Protocol. BSCI Module 4 Lesson 1 Introducing IS-IS and Integrated IS-IS Routing. 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

Download Presentation

The IS-IS Protocol

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


The IS-IS Protocol

BSCI Module 4 Lesson 1

Introducing IS-IS and Integrated IS-IS Routing


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


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


Uses for IS-IS Routing

Large ISPs

  • Stable protocol

  • Originally deployed by ISPs because US government mandated internet support of OSI and IP


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.


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.


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.


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.


Integrated IS-IS Design Principles

  • IP and CLNP addressesmust 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


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.


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.


Four OSI Routing Levels


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.


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


Advantages of Integrated IS-IS

  • Supports CLNP and IP

  • More extensible through Type, Length, Value (TLV) design


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.


Comparison of Integrated IS-IS and OSPF

The following table summarizes the differences between OSPF and integrated IS-IS.


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.

  • .


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.

  • .


Activity

  • List all of the features of both IS-IS and OSPF and compare the advantages and disadvantages of both.


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?


Additional Links

  • http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800c5bc1.html

  • http://www.certificationzone.com/cisco/newsletter/SL/IE-ISIS-WP2-F02_BIF.html

  • http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfisis.htm

    • .


Q and A


  • Login