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© 2001, Cisco Systems, Inc. 2-1 A_ISIS_Primer Overview of IS-IS Technologies, Structures and Protocols.

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Presentation on theme: "© 2001, Cisco Systems, Inc. 2-1 A_ISIS_Primer Overview of IS-IS Technologies, Structures and Protocols."— Presentation transcript:

1 © 2001, Cisco Systems, Inc. 2-1 A_ISIS_Primer Overview of IS-IS Technologies, Structures and Protocols

2 © 2001, Cisco Systems, Inc Objectives Upon completion of this lesson, you will be able to to perform the following tasks : Describe the OSI protocol suite with special attention to the network layer Explain the principles of OSI routing List the prerequisites for the implementation of the IS-IS routing model in a network List the types of IS-IS routers and explain the principle of area routing Explain the purpose of Integrated IS-IS Configure, monitor and troubleshoot a simple IS-IS network

3 Introduction to OSI Protocols and IS-IS Routing © 2001, Cisco Systems, Inc. Overview of ISIS Technologies, Structures and Protocols 3

4 © 2001, Cisco Systems, Inc Objectives Upon completion of this section, you will be able to: Explain the terminology used in OSI List routing protocol examples for routing OSI protocols Describe the basic concepts of link-state routing Make a general comparison between Integrated IS-IS and OSPF

5 © 2001, Cisco Systems, Inc OSI Protocols ISO and OSI? The International Organization for Standardization (ISO) has been constituted to develop standards for data networking. The Open System Interconnection (OSI) protocols represent an international standardization program that facilitates multivendor equipment interoperability.

6 © 2001, Cisco Systems, Inc OSI Protocols(cont.) The OSI protocol suite supports Numerous standard protocols at each of the OSI seven layers reference model OSI network-layer hierarchical addressing Two routing protocols at the network layer

7 © 2001, Cisco Systems, Inc OSI Protocols Terminology Terminology used in OSI End System (ES) is any non-routing network nodes (host) Intermediate system (IS) is a router An area is a logical entity –Formed by a set of contiguous routers, hosts and the data links that connect them Domain is a collection of connected areas

8 © 2001, Cisco Systems, Inc OSI Protocol Suite and its Mapping to the OSI Reference Model

9 © 2001, Cisco Systems, Inc OSI Network Services What to Route in OSI Environment? Two types of OSI network-layer services are available to the OSI transport layer: Connectionless Network Service (CLNS) –CLNS performs datagram transport Connection-mode Network Service (CMNS) –CMNS requires explicit establishment of paths between communicating transport- layer entities

10 © 2001, Cisco Systems, Inc OSI Network Services Connection-oriented Mode CMNS/CONP: CONP is an OSI network-layer protocol that carries upper-layer data and error indications over connection-oriented links CMNS performs functions related to the explicit establishment of paths via CONP When support is provided for CMNS, the routing uses the X.25 protocols as the relaying functions

11 © 2001, Cisco Systems, Inc OSI Network Services Connectionless Mode CLNS/CLNP: CLNP is a an OSI network-layer protocol that carries upper-layer data and error indications over connectionless links CLNS provides network-layer services to the transport layer via CLNP When support is provided for CLNS, the routing uses routing protocols to exchange routing information

12 © 2001, Cisco Systems, Inc OSI Network ServicesRouting Protocols ISO has developed standards for two types of protocols: ES-IS dicovery protocols: routing between End Systems and Intermediate Systems referred as level-0 routing IS-IS routing protocols: hierarchical (level-1, level-2 and level-3) routing between Intermediate Systems

13 © 2001, Cisco Systems, Inc OSI Network ServicesOSI Routing in Operation Area-1 Area-2 IS ES Domain Level-0 routing between ESs and ISs on the same subnet Level-1 routing between ISs within the same area Level-2 routing between different areas within the same domain Level-3 routing between separate domains

14 © 2001, Cisco Systems, Inc OSI Network ServicesIS-IS Routing Intermediate System to Intermediate System (IS-IS) is a dynamic link-state routing protocol in ISO CLNS environment for routing CLNP Link-state routing protocol in the OSI stack Alternative to IS-IS protocols is deploying CISCO ISO-IGRP or static routing

15 © 2001, Cisco Systems, Inc OSI Network Services Recommended Reading ISO 8473documents the ISO Connectionless Network Protocol (CLNP) ISO/IEC 8348 appendix Adocuments NSAP addresses ISO 9542documents the ES-IS routing exchange protocol ISO/IEC 10589documents IS-IS intra- domain routing exchange protocol

16 © 2001, Cisco Systems, Inc Basic Terms of Link-State Routing Protocols Link-state (LS) routers know much more about the network than their distance- vector relativesLS routers cannot be fooled as easily into making wrong decisions Link-state routers keep track of: Their neighbors All the routers in the network, or at least within the same area Best paths toward a destination

17 © 2001, Cisco Systems, Inc Basic TermsLink-State Data Structures Neighbor table, formally known as an adjacency database (list of neighbors we are aware of) Topology table, typically referred to as a link-state databaseLSDB (routers and links in the area/network) Routing table, commonly named a forwarding database (list of best paths to destinations)

18 © 2001, Cisco Systems, Inc Basic TermsThe Best Path Calculation Routers find the best paths to destinations by applying the Dijkstra Shortest Path First (SPF) algorithm to the link-state database Every router in the area places itself into the root of the tree that is built Best path is calculated with respect to the lowest total cost of links to a specific destination Best routes are put into the forwarding database

19 © 2001, Cisco Systems, Inc Basic TermsLink-State Environment x C A B E D G F H Link-state database Adjacency database Neighbors of x: A, B,C,D C A B E D G F H Dijkstra (SPF) algorithm Forwarding database (routing table) Shortest paths x

20 © 2001, Cisco Systems, Inc Examples of Link-State Protocols OSPF (Open Shortest Path First), supports IP only; Internet standard DECnet Phase V, supports Decnet/OSI IS-IS (supports CLNP); ISO standard Integrated IS-IS (supports CLNS and IP); Internet standard, RFC-1195 NLSP (Netware Link Services Protocol), supports IPX only, based on IS-IS PNNI (Private Network to Network Interface) used in ATM routing

21 © 2001, Cisco Systems, Inc Link-State Data Structure Network Hierarchy Link-state routing requires a hierachical network structure Enforced by some LS protocols (for example, OSPF) Some LS protocols are more tolerant (IS-IS) Two level hierarchyareas Backbone or level-2 area Non-backbone or level-1 area

22 © 2001, Cisco Systems, Inc LS Data StructuresLink-State Database The foundation for best-path calculation is the LS database LS database has to be identical on all the routers in the areaidentical view Routers know everything about their respective area Routers know about the nearest exit point(s) to other areas or other routing domains

23 © 2001, Cisco Systems, Inc LS Data StructuresAdjacency Database Routers discover neighbors by exchanging Hello packets Routers declare neighbors UP after checking some parameters/options Some routers become adjacent (tightly connected neighbors)good neighbors Adjacent routers exchange topology information

24 © 2001, Cisco Systems, Inc LS Data StructuresLink-State Packets Upon establishing neighbor relationship, routers exchange their pictures of the network Full picturelink-state database (LSDB)is built by link-state packets (LS packets) LS packets report the states of links and routers LS packets are flooded reliably throughout the area/network

25 © 2001, Cisco Systems, Inc LS Data StructuresOriginating Link-State Packets LS packets contain router information (state, interfaces, addresses, connected routers) Originator of LS packet is a router itself LS packets are sequenced to prevent reflooding of the routers own LS packet LS packets are aged when in the LS databaseageing out results in purging the packet Periodic refreshments of LS packets to prevent ageing out

26 © 2001, Cisco Systems, Inc LS Data StructuresLink-State Maintenance Routers maintain the consistency of the link-state database Routers check their neighbor relationship by sending and receiving periodic hello packets Routers report changes in the network (immediately/depending on timers) Receivers of a link-state packet normally flood it further Routers periodically resend their part of the network map (even if no changes)

27 © 2001, Cisco Systems, Inc Link-State Processes

28 © 2001, Cisco Systems, Inc Link-State ProcessesReceive and Update Receive process: Receives datagrams Forwards data to the Forward process Forwards routing protocol packets to the Update process Update process: Creates link-state information Receives link-state information from neighbors Builds and maintains the link-state database

29 © 2001, Cisco Systems, Inc Link-State ProcessesDecision and Forward Decision process Creates forwarding database by running Dijkstra algorithm on the link-state database Forward process Receives packets from the Receive process Forwards packets according to the forwarding database Manages load sharing, redirection and error reporting

30 © 2001, Cisco Systems, Inc Benefits of Link-State Routing Benefits: Fast convergencechanges reported immediately by the source affected Robustness against routing loops: –Routers know the topology –LS packets numbered and acknowledged By careful (hierarchical) network design resources can be utilized optimally

31 © 2001, Cisco Systems, Inc Caveats of Link-State Routing Caveats: Significant demands for resources: –Memory (three tables: adjacency, topology, forwarding) –CPU (Dijkstra algorithm can be intensive, especially when a lot of instabilities are present) Requires very strict network design (when more areasarea routing) Problems with partitioning of areas

32 © 2001, Cisco Systems, Inc Configuration generally simple but can be complex when tuning various parameters and when the design is complex Troubleshooting is easier than in distance vector routingwe have more information at hand (three databases) Requires a good understanding of link-state concepts Benefits and Caveats of Link- State Routing

33 © 2001, Cisco Systems, Inc Integrated IS-IS vs. OSPF Integrated IS-IS is an extended version of IS-IS for mixed ISO CLNS and IP environments Integrated IS-IS (RFC1195) represents an alternative to OSPF in the IP world Integrated IS-IS and OSPF are both link-state protocols with similar: –Link-state representation, ageing, metrics –Links-state databases, SPF alghoritms –Update, desicion and flooding processes

34 © 2001, Cisco Systems, Inc Integrated IS-IS vs. OSPFArea Design Area design OSPF is based on a central backbone with all other areas being attached to it –In OSPF the border is inside routers (ABRs) –Each link belongs to one area In IS-IS the area borders lie on links –Each IS-IS router belongs to exactly one area –IS-IS allows a more flexible approach to extending the backbone

35 © 2001, Cisco Systems, Inc Integrated IS-IS vs. OSPF (cont.) Resource usage One link-state packet per IS-IS router in one area (including redistributed prefixes) compared to many OSPF LSAs Scalability of link-state protocols has been proved (live ISP backbones) Convergence capabilities are similar (same algorithm) OSPF has more features (route tags, Stub/NSSA, OSPF over Demand Circuit…)

36 © 2001, Cisco Systems, Inc Summary After completing this section, you should be ready to: Explain the terminology used on OSI List routing protocol examples for routing OSI protocols Describe the basic concepts of link-state routing Make a general comparison between Integrated IS-IS and OSPF

37 © 2001, Cisco Systems, Inc Review Questions Explain the meaning of the following abbreviations: OSI, ISO, IS and ES. How do ESs and ISs communicate? What types of network services does an OSI protocol stack support? Explain the CLNPs position in an OSI stack. How many routing levels are supported in OSI routing? List the protocols that can be used for routing CLNS/CLNP. What are the differences between distance-vector and link-state routing protocols? What is common to OSPF and Integrated IS-IS?

38 Operation of IS-IS © 2001, Cisco Systems, Inc. Overview of ISIS Technologies, Structures and Protocols 2- 38

39 © 2001, Cisco Systems, Inc Objectives Upon completion of this section, you will be able to: Prepare a proper addressing plan for IS-IS deployment Explain how networks and interfaces are represented in IS-IS List the types of IS-IS routers and their role in IS-IS area design Describe the hierarchical structure of IS-IS areas Describe the concept of establishing adjacencies Describe the concepts of routing traffic transport and database synchronization

40 © 2001, Cisco Systems, Inc ISO IS-ISIS-IS PDU IS-IS Protocol Data Units (PDU) are encapsulated directly into a data-link frame There is no CLNS or IP header in a PDU: Hello (ESH, ISH, IIH) LSP (Non-pseudonode and Pseudonode) PSNP (Partial Sequence Numbers PDU) CSNP (Complete Sequence Numbers PDU)

41 © 2001, Cisco Systems, Inc ISO IS-IS PDU(cont.) PDU (Protocol Data Unit) between peers Network PDU = datagram, packet Data Link PDU = frame Data-link header (OSI family 0xFEFE) IS-IS header (first byte is 0x83) IS-IS TLVs IS-IS: Data-link header (OSI family 0xFEFE) ES-IS header (first byte is 0x82) ES-IS TLVs ES-IS: Data-link header (OSI family 0xFEFE) CLNP header (first byte is 0x81) CLNS CLNP

42 © 2001, Cisco Systems, Inc OSI Address Assignment OSI network layer addressing is implemented with network service access point (NSAP) addresses NSAP address identifies any system in OSI network Various NSAP formats for various systems –Different protocols may use different representation of NSAP

43 © 2001, Cisco Systems, Inc IS-IS NSAP AddressStructure IS-IS (ISO/IEC 10589) distinguishes only 3 fields in NSAP address: Area Address: variable length field composed of high order octets excluding SystemID and SEL SystemID: ES or IS identifier in an area; fixed length of 6 octets in Cisco IOS NSEL: N-selector, service identifier

44 © 2001, Cisco Systems, Inc OSI AddressingIS-IS vs. ISO- IGRP NSAPs IS-IS NSAP is divided into three parts 1 octet NSEL, 6 octets for System ID and from 1 to 13 octets for Area Address field Total length of NSAP from 8 (minimum) up to 20 octets (maximum ) ISO-IGRP NSAP is divided as follows: Area Address, composed of the first two octets of the NSAP after the System ID and NSEL fields Domain, composed of high order octets (from 1 to 11) of the NSAP, excluding the Area, System ID and NSEL fields ISO-IGRP requires at least 10 bytes of NSAP

45 © 2001, Cisco Systems, Inc OSI AddressingNetwork Entity Title Network Service Access Point (NSAP) address which (at the network layer) includes a service identifier (protocol number) Network Entity Title (NET)NSAP with service identifier of 00 Used in routers since they implement network layer only (base for SPF calculation) The official NSAP prefixes are required for CLNS routingAFI 49 (Authority and Format Identifier) denotes private address space

46 © 2001, Cisco Systems, Inc OSI AddressingNET and System Identifier Rules NET must begin with an octet 47.xxxx....; 0111.xxxx... Not 111.xxxx... NET must end with a single octet set to 00, identifying network entity (e.g. router) itself...xxxx.00 System ID normally six octets (on Cisco six!) and has to be the same length everywhere Examples: c

47 © 2001, Cisco Systems, Inc OSI AddressingNSAP Examples Example 1: NSAP aaaa.bbbb.cccc.00 IS-IS: Area = , System ID = aaaa.bbbb.cccc, NSEL = 00 ISO-IGRP: Domain = 47 Area = 0001, System ID = aaaa.bbbb.cccc, NSEL = 00 Example 2: NSAP 39.0f c IS-IS: Area = 39.0f , Sysem ID = c , NSEL = 00 ISO-IGRP: Domain= 39.0f01 Area = 0002, System ID = c , NSEL = 00

48 © 2001, Cisco Systems, Inc Identifying Systems in IS-IS The Area Address uniquely identifies the routing area and the System ID identifies each node All routers within an area must use the same Area Address An ES may be adjacent to a level-1 router only if they both share a common Area Address Area Address is used in level-2 routing

49 © 2001, Cisco Systems, Inc Identifying Systems in IS-IS System ID System ID may be the MAC address (CLNS) or IP address of an interface (IP world) System ID used in level-1 routing and has to be unique within an area (and of same length) System ID has to be unique within level-2 routers that form routing domain General recommendation: domain-wide unique System ID

50 © 2001, Cisco Systems, Inc Identifying Systems Subnetwork and Circuit SNPA (Subnetwork Point of Attachment) identified by: Encapsulation type or DLCI address on p2p interfaces (HDLC, FR) MAC address on LAN interfaces (0000.0c ) Interfaces uniquely identified by Circuit ID: One octet number on point-to-point interfaces (03) Circuit ID concatenated with 6 octet System ID of a designated router on broadcast multi-access networks to form 7 octet LAN ID ( )

51 © 2001, Cisco Systems, Inc Identifying SystemsOSI Addressing in Network

52 © 2001, Cisco Systems, Inc Link State PacketsNetwork Representation Generally physical links can be placed in two groups: Broadcastmulti-access subnetworks that support addressing of a group of attached systems (LANs) Point-to-point links, multi-point links, dynamically established links Only two link-state representations are available in IS-IS: Broadcast for LANs Point-to-point for all other topologies

53 © 2001, Cisco Systems, Inc Link State Packets Representing Routers Router describes itself with the Link State Packet (LSP) LSP header contents: –PDU type, Length, LSP ID, Sequence Number, Remaining Lifetime Type Length Value (TLV) variable length fields: –IS neighbors –ES neighbors –Authentication Information –.... LSP Header IS neighbors ES neighbors

54 © 2001, Cisco Systems, Inc LSP Representing RoutersLSP Header LSPs are numbered by a sequence number to prevent duplicates LSPs Assists with synchronization Sequence numbers begin with 1 Sequence numbers are increased to indicate newest LSP LSPs in LSDB have a remaining lifetime Allows synchronization Decreasing timer

55 © 2001, Cisco Systems, Inc LSP Representing Routers Variables Router specific information is encoded in the variable field with TLVs (Type Length Value) Metric is associated with an outgoing interface Four types (three optional, intended to be used in Type-of-Service routing) Delay, default, expense and errorCisco uses default metric only

56 © 2001, Cisco Systems, Inc LSP Representing RoutersLAN Representation IS DIS IS Pseudonodelogically connected to all other nodes NOTE: All (physical) routers still establish adjacency to each other Logical Phisycal

57 © 2001, Cisco Systems, Inc L1, L2 and L1/L2 Routers Two-level structure of areas forms IS-IS domains Intermediate Systems can be: L1, level-1 (equivalent to OSPF internal non- backbone routers), responsible for intra-area routing L1/L2, level-1-2 (in OSPF these are area-border routers), performing intra- and inter-area routing L2, level-2 (backbone routers in OSPF), inter-area only

58 © 2001, Cisco Systems, Inc L1 and L2 Routers Level-1 (L1) routers referred to as Station routers L1 routers constitute an area L1 routers keep one copy of the link-state database (its own area picture; intra-area information only) They enable stations (ESs) to communicate Level-2 (L2) routers referred to as Area routers They store inter-area information They interconnect areas

59 © 2001, Cisco Systems, Inc L1/L2 Router Level-1-2 (L1/L2) routers keep two separate copies of the link-state databases For level-1 and level-2 Inform L1 routers about an exit point Level-1 area is a collection of L1 and L1/L2 routers Backbone area (level-2) is a set of L1/L2 and L2 routers and has to be contiguous

60 © 2001, Cisco Systems, Inc L1, L2 and L1/L2 LSP Features Two-level nature of IS-IS requires separate types of link-state packets level-1 and level-2 LSPs Designated IS is a representative of a LAN and performs additional duties Pseudo level-1 and level-2 LSPs on behalf of the LANseparate DIS for L1 and L2; no backup DIS LSPs sent to a unicast address on point-to- point links and to a multicast address on broadcast multi-access networks

61 © 2001, Cisco Systems, Inc Example #1: Area ConfigurationPhysical View Area-1 Area-2 R3 R2 R1 R4 L1L2 routers L1 routers R2 and R3 belong to their respective level-1 areas and provide a physical connection between them

62 © 2001, Cisco Systems, Inc Example #1: Area ConfigurationLogical View L1 R3 R2 R1 R4 R2 and R3 are still L1 routers but in addition they provide an entry point to the level-2 backbone interconnecting both level-1 areas L2 L1

63 © 2001, Cisco Systems, Inc Example #2: L2 and L1/L2 Routers Forming L2 Backbone L1L2 Backbone links L1L2 L1-only L2-only L1-only Area-2 Area-1 Area-3 Area-4 L1-only L1L2 IS-IS domain This router must behave as level-2 as well in order to guarantee backbone continuity.

64 © 2001, Cisco Systems, Inc Identifying Types of Systems Hello Messages Periodic hello messages (Hello PDU) are used, as in any other link-state protocol Three types: ESH (End System Hello), between ES and IS ISH (Intermediate System Hello), sent by IS to ES IIH (IS to IS Hello, used between two ISs) Hellos carry information on the system itself, its capabilities and interface parameters

65 © 2001, Cisco Systems, Inc Identifying Types of Systems ES and IS Hello Packets ES IS-IS IS ES-IS IS SNPA ES IS SNPA ESH ISH IIH

66 © 2001, Cisco Systems, Inc IS-IS and ES-IS Communication Intermediate Systems establish and maintain neighbor relationships through the use of IS to IS hellos (IIH) Then they exchange LSPs End Systems do not need any configuration for finding their respective IS End Systems listen to IS hellos (ISH) to find their way to the world Initially ES picks a router randomly (whichever is heard)

67 © 2001, Cisco Systems, Inc IS-IS and ES-IS Communication (cont.) Routers listen to ESH and thus find all the end systems on a segment Routers include information on End Systems in link-state packets Routers send Redirect message to help ES in finding the most optimal exit from a segment

68 © 2001, Cisco Systems, Inc Neighbors and Adjacencies IIH (IS to IS Hello) between routers Two types of Hellos on LANL1 and L2 Only one on p2p (with the type of desired adjacency describedL1, L2 or both) Hellos sent every 10 seconds, hold-time 30 seconds (default) Separate adjacencies are built for L1 and L2 routers L1/L2 routers keep two tables Routers form adjacencies with all other routers and send LSPs to all routers on the LAN (unlike OSPF routers)

69 © 2001, Cisco Systems, Inc LAN Adjacencies L1 L1/L2 L1 L1 adjacency L2 adjanceny Adjacencies are established based on the area address announced in the incoming IIHs and the type of the router L1/L2 Area-1 Area-2

70 © 2001, Cisco Systems, Inc WAN Adjacencies L1 L1/L2 Area-1 L1/L2 L1 L1/L2 Area-1 L1 L2 Area-1 Area-2 L1 L1L2 L1 # L1/L2 L2 L1/L2 Area-1 L2 L1/L2 L2 L1/L2 Area-1 Area-2 L2 L1/L2 Area-1

71 © 2001, Cisco Systems, Inc Continous Flow of L2 Adjacencies L1L2 L2-only L1-only L1L2 Area-1 Area-2 Area-3 L1 adjacencies L2 adjacencies L1 and L2 adjacencies Area-1 and Area-2 are level-1 areas Level-2 backbone is a set of L1/L2 and L2 routers and overlaps attached level-1 areas

72 © 2001, Cisco Systems, Inc Update, Decision and Flooding Processes No routes calculated before the map of the network builtno map built before adjacencies established The network map is built through an Update process in the router Network changes reflected immediately (depending on timer settings) through link- state updates

73 © 2001, Cisco Systems, Inc Update, Decision and Flooding Processes SPF topology based on NETs IP subnets are treated similarly to ES (in LSP and link-state database) Changes of IP information (or ESs) do not lead to full SPF recalculationpartial route calculation (PRC) run onlyoptimization

74 © 2001, Cisco Systems, Inc Update, Decision and Flooding Processes LSP originated at the source of a change (for example, link coming up) LSP received by other routers and flooded in a controlled way through all the adjacencies LSPs periodically reflooded to refresh the link-state database (Remaining Lifetime) SNP (Sequence Numbers PDU) packets used to ensure synchronization and reliability

75 © 2001, Cisco Systems, Inc LSDB Synchronization SNP (Sequence Number PDU) packets used to ensure synchronization and reliability Contents are LSP descriptions PSNP (Partial SNP) used: For acknowledgment of LSPs on p2p links To request missing pieces of link-state database CSNP (Complete SNP) used: Periodically by DIS on LAN to ensure reliability On point-to-point link when the link comes up

76 © 2001, Cisco Systems, Inc LSDB SynchronizationP2P R1 R3 LSP 33 PSNP III. ACK: Thank you for LSP 33 I. Link went down II. New LSP describing the current situation s0 R2

77 © 2001, Cisco Systems, Inc LSDB SynchronizationLAN R1 CSNP sent periodically (every 10 s) by DIS R2/DIS PSNP II. Request: Sorry. I missed LSP 77 CSNP PSNP I. CSNP: LSP76 LSP77 LSP88

78 © 2001, Cisco Systems, Inc Summary After completing this section, you should be able to: Prepare a proper addressing plan for IS-IS deployment Explain how networks and interfaces are represented in IS-IS List the types of IS-IS routers and their role in IS-IS area design Describe the hierarchical structure of IS-IS areas Describe the concept of establishing adjacencies Describe the concepts of routing traffic transport and database synchronization

79 © 2001, Cisco Systems, Inc Review Questions How is the router identified in an IS-IS environment? What is the difference between NSAP and NET? What does a unique System ID define? Which network representations are supported by IS- IS? What is a pseudonode? List the types of IS-IS routers. How do two level-1 areas communicate? How do systems find each other in IS-IS? List the types of adjacencies between IS-IS systems. How is LSDB synchronization done in IS-IS?

80 IP and OSI Routing with Integrated IS-IS © 2001, Cisco Systems, Inc. Overview of ISIS Technologies, Structures and Protocols 2-80

81 © 2001, Cisco Systems, Inc Objectives Upon completion of this section, you will be able to perform the following tasks: Determine how CLNS and IP networks are represented in LSPs Determine how a router builds OSI and IP forwarding tables Explain the basic principles of area routing

82 © 2001, Cisco Systems, Inc Integrated IS-IS Routing Protocol Integrated IS-IS allows for three types of routing domains (OSI, IP, Dual) Therefore, an IS-IS LSP may contain multiple variable length fields (TLV) Some contain OSI-specific information Some contain IP-specific information

83 © 2001, Cisco Systems, Inc Integrated IS-ISRepresenting IP Networks LSP describes IP information in the same way as ESs Integrated IS-IS has all the features of modern routing protocols Variable length mask Redistribution Summarization

84 © 2001, Cisco Systems, Inc Integrated IS-ISNET Address Planning Common CLNS parameters (NET) and Area planning are still required even in an IP environment Even when Integrated IS-IS is used only for IP routing, routers still establish CLNS adjacencies and use CLNS packets

85 © 2001, Cisco Systems, Inc OSI Area RoutingBuilding OSI Forwarding Table When databases are synchronized, Dijkstra (SPF) algorithm is run on the LSDB to calculate the SPF tree Criteria: the shortest path to the destination is the lowest total sum of metrics Separate route calculations made for L1 and L2 areas in L1/L2 routers Partial route calculation (PRC) run to calculate ES reachability Best paths are placed in the OSI L1 and the L2 forwarding table

86 © 2001, Cisco Systems, Inc OSI Area Routing Level-1 intermediate systems Routing within the area is based on the System ID portion of the ISO address If the destination belongs to another area, they route to the nearest active level-1-2 router Level-2 intermediate systems Routing between areas is based on the Area Address and considers only the area cost If the destination belongs to the same area, they use the least-cost path to the System ID

87 © 2001, Cisco Systems, Inc OSI Area RoutingRouting Between Areas From level-1 via level-2 to level-1 L1 always sends a packet to a nearest active L1/L2 router (default routing) Then the packet travels via L2 routing towards the destination area where the best L1 path is used Note: L1/L2 router performs L1 and L2 routing

88 © 2001, Cisco Systems, Inc OSI Area RoutingSuboptimal Inter-area Routing L1L2 L2 Area-2 Area-1 Area-3 Area-4 Area-5 R2 R1 Network path from router R2 to R1 Network path from router R1 to R2 L R2 takes the closest exit; then L1L2 takes the closest entry 10

89 © 2001, Cisco Systems, Inc OSI Area Routing Interconnecting IS-IS Domains IS-IS routing domain is a collection of IS- IS areas When interconnecting IS-IS domains the following applies: In pure IP-environment use BGP In pure CLNS use ISO-IGRP or static CLNS routes

90 © 2001, Cisco Systems, Inc Example #1: OSI Intra- and Inter- area Routing Area Area R5 - L2 R2 - L1L2 R1 - L1 L2 L1 Routing in a two-level area structure R4 - L1 L1 S0 S1 S0 S1 E0

91 © 2001, Cisco Systems, Inc Example #1Level-1 and Level-2 Topology Table R1#show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA R1 -- R2 10 R2 Se0 *HDLC* R4 10 R4 Se1 *HDLC* R2#show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA R1 10 R1 Se0 *HDLC* R2 -- R4 10 R4 Se1 *HDLC* IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA R2 -- R5 10 R5 Et bb5.9e20

92 © 2001, Cisco Systems, Inc Example #1Intra-area Routing on R1 R1#show clns route CLNS Prefix Routing Table , Local NET Entry R1#show isis route IS-IS Level-1 Routing Table - version 312 System Id Next-Hop Interface SNPA Metric State R2 R2 Se0 *HDLC* 10 Up L2-IS R4 R4 Se1 *HDLC* 10 Up R1 -- Default route out of area - (via 2 L2-attached ISs) System Id Next-Hop Interface SNPA Metric State R2 Se0 *HDLC* 10 Up

93 © 2001, Cisco Systems, Inc Example #1Intra- and Inter-area Routing on R2 R2#show clns route CLNS Prefix Routing Table , Local NET Entry [110/10] via R5, IS-IS, Up, Ethernet [110/0] via R2, IS-IS, Up R2#show isis route IS-IS Level-1 Routing Table - version 47 System Id Next-Hop Interface SNPA Metric State R4 R4 Se1 *HDLC* 10 Up R1 R1 Se0 *HDLC* 10 Up

94 © 2001, Cisco Systems, Inc Example #1Which Route in L1? R1#which-route (R2 NSAP) Route look-up for destination Found route in IS-IS level-1 routing table Adjacency entry used: System Id Interface SNPA State Holdtime Type Protocol Se0 *HDLC* Up 26 L1 IS-IS Area Address(es): Uptime: 00:09:50 R1#which-route (R5 NSAP) Route look-up for destination Using route to closest IS-IS level-2 router Adjacency entry used: System Id Interface SNPA State Holdtime Type Protocol Se0 *HDLC* Up 27 L1 IS-IS Area Address(es): Uptime: 00:09:57

95 © 2001, Cisco Systems, Inc Example #1Which Route in L2? R5#which-route (R2 NSAP) Found route in CLNS L2 prefix routing table Route entry used: i [110/10] via R2, Ethernet0/0 Adjacency entry used: System Id Interface SNPA State Hold. Type Prot R2 Et0/ c92.e515 Up 24 L2 IS-IS Area Address(es): R5#which-route (R1 NSAP) Found route in CLNS L2 prefix routing table Route entry used: i [110/10] via R2, Ethernet0/0 Adjacency entry used: System Id Interface SNPA State Hold. Type Prot. R2 Et0/ c92.e515 Up 21 L2 IS-IS Area Address(es):

96 © 2001, Cisco Systems, Inc Building IP Forwarding Table PRC is also run to calculate IP reachability Since IP and ES are represented as leaf objects they do not participate in SPF Best paths are placed in the IP forwarding table following IP preferential rules They appear as L1 or L2 IP routes

97 © 2001, Cisco Systems, Inc Building IP Forwarding Table (cont.) Area Area R5- L2 R2 - L1L2 R1 - L1 L2 L1 R4 - L1 L1 The IP addresses on loopbacks of routers are /8- R1, /8-R2, /8-R4 and /8-R5. R2#sh ip route i L /8 [115/10] via , Ser0 -(R1) i L /8 [115/10] via , Ser1 -(R4) i L /8 [115/10] via , Eth0 -(R5) S0 S1 E0

98 © 2001, Cisco Systems, Inc Summary After completing this section, you should be able to perform the following tasks: Determine how CLNS and IP networks are represented in LSPs Determine how a router builds OSI and IP forwarding tables Explain the basic principles of area routing

99 © 2001, Cisco Systems, Inc Review Questions What is Dual ISIS? Is a NET address still required even when Integated IS-IS is run only for IP? How are IP subnets represented in the IS-IS environment? Describe the process of building OSI and IP forwarding tables? What is the principle of area routing?

100 Basic Integrated IS-IS Router Configuration © 2001, Cisco Systems, Inc. Overview of ISIS Technologies, Structures and Protocols 2-100

101 © 2001, Cisco Systems, Inc Objectives Upon completion of this section, you will be able to perform the following tasks: Configure Cisco routers for basic Integrated IS-IS operation Inspect basic Integrated IS-IS parameters on Cisco routers

102 © 2001, Cisco Systems, Inc Integrated IS-IS Configuration Steps Step1: Define areas, prepare addressing plan (NETs) for routers and determine interfaces Step2: Enable IS-IS in a router Step3: Configure the NET Step4: Enable Integrated IS-IS on the proper interfacesdo not forget interfaces to stub IP networks, such as loopbacks (although no CLNS neighbors there)

103 © 2001, Cisco Systems, Inc router isis [tag] router(config)# Enable the IS-IS routing protocol; tagname for a process; when routing of clns packet is also needed use the clns routing command IS-IS Configuration StepsIS-IS Survival Kit Commands ip router isis [tag] clns router isis [tag] router(config-if)# Start an IS-IS routing process on an interface (IP, CLNS, both) net network-entity-title router(config-router)# Configure an IS-IS NET address for the routing process

104 © 2001, Cisco Systems, Inc is-type {level-1 | level-1-2 | level-2-only} router(config-router)# Configure the IS-IS level globally on a router; default = L1/L2 (station/area) IS-IS Configuration StepsIS-IS Good to Know Commands isis circuit-type {level-1 | level-1-2 | level-2-only} router(config-if)# Configure the type of adjacency on an interface; default = L1/L2 isis metric default-metric {level-1 | level-2} router(config-if)# Configure the metric for an interface; default = 10

105 © 2001, Cisco Systems, Inc IS-IS Configuration Steps Simple Integrated IS-IS Example The configured router acts as IP-only L1/L2 router router isis net ! interface ethernet 0 ip address ip router isis ! interface serial 0 ip address ip router isis router isis net ! interface ethernet 0 ip address ip router isis ! interface serial 0 ip address ip router isis

106 © 2001, Cisco Systems, Inc Example #1: Sample Two-area Configuration Area Area R3 R2 R1 R4 L1L2 routers L1 routers E0 S0 Configure routers for routing IP within two- level area structure S0 E0

107 © 2001, Cisco Systems, Inc Example #1: Sample Two-area Configuration (L1 routers) R1 has to be L1-only router hostname R1 ! interface Serial0 ip address ip router isis ! router isis is-type level-1 net hostname R1 ! interface Serial0 ip address ip router isis ! router isis is-type level-1 net

108 © 2001, Cisco Systems, Inc Example #1: Sample Two-area Configuration (L1/L2 routers) R2 has to be L1/L2-router (optimized) hostname R2 ! interface Ethernet0 ip address ip router isis isis circuit-type level-2 ! interface Serial0 ip address ip router isis isis circuit-type level-1 ! router isis net hostname R2 ! interface Ethernet0 ip address ip router isis isis circuit-type level-2 ! interface Serial0 ip address ip router isis isis circuit-type level-1 ! router isis net

109 © 2001, Cisco Systems, Inc show clns router# Display information about the CLNS network Troubleshooting Commands CLNS show clns protocol [tag] router# List the protocol-specific information show clns interface [type number] router# List the CLNS-specific information about each interface show clns neighbors [type number] [detail] router# Display both ES and IS neighbors

110 © 2001, Cisco Systems, Inc show isis route router# Display IS-IS level-1 routing table Troubleshooting Commands CLNS and IS-IS show clns route router# Display CLNS routing table show isis database router# Display the IS-IS Link-State database

111 © 2001, Cisco Systems, Inc show ip protocols router# Display the parameters and current state of the active routing protocol process Troubleshooting CommandsIP show ip route [address [mask]] | [protocol [process-id]] router# Display the current state of the routing table

112 © 2001, Cisco Systems, Inc Example #2: Simple Troubleshooting What About CLNS Protocol? R2#show clns protocol IS-IS Router: System Id: IS-Type: level-1-2 Manual area address(es): Routing for area address(es): Interfaces supported by IS-IS: Serial0 - IP Eethernet0 - IP Redistribute: static (on by default) Distance for L2 CLNS routes: 110 RRR level: level-1 Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none

113 © 2001, Cisco Systems, Inc Example #2: Are Adjacencies Established? R2#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol R1 Se0 *HDLC* Up28L1IS-IS R3 Et c92.de4c Up20L2IS-IS R2#show clns interface serial 0 Serial0 is up, line protocol is up Checksums enabled, MTU 1500, Encapsulation HDLC ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 12 seconds Routing Protocol: IS-IS Circuit Type: level-1 Interface number 0x1, local circuit ID 0x101 Level-1 Metric: 10, Priority: 64, Circuit ID: R2.00 Number of active level-1 adjacencies: 1 Next IS-IS Hello in 5 seconds

114 © 2001, Cisco Systems, Inc Example #2: Is Integrated IS-IS Running? R2#show ip protocols Routing Protocol is "isis" Sending updates every 0 seconds Invalid after 0 seconds, hold down 0, flushed after 0 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: isis Address Summarization: None Routing for Networks: Serial0 Ethernet0 Routing Information Sources: Gateway Distance Last Update :11: :11: :11:44 Distance: (default is 115)

115 © 2001, Cisco Systems, Inc Example #2: Do We See Any IP Routes? R2#show ip route isis i L /8 [115/10] via , Serial0 i L /8 [115/10] via , Ethernet0 i L /8 [115/20] via , Ethernet0

116 © 2001, Cisco Systems, Inc Summary After completing this section, you should be able to perform the following tasks: Configure Cisco routers for basic Integrated IS- IS operation Inspect Cisco routers IS-IS configuration at an entry level

117 © 2001, Cisco Systems, Inc Review Questions How is IS-IS routing enabled on Cisco routers? In which configuration mode are NETs defined? List at least two commands for checking CLNS parameters on a Cisco router. How are IP routes found that were added to the routing table by Integrated IS-IS?

118 © 2001, Cisco Systems, Inc Summary After completing this lesson, you should be able to: Describe the OSI protocol suite with special attention to the network layer Explain the principles of OSI routing List the prerequisites for the implementation of the IS-IS routing model in a network List the types of IS-IS routers and explain the principle of area routing Explain the purpose of Integrated IS-IS Configure, monitor and troubleshoot a simple IS-IS network

119 © 2001, Cisco Systems, Inc. Overview of IS-IS Technologies, Structures and Protocols 119

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