1 / 60

The IS-IS Protocol

The IS-IS Protocol. SAvPS Genci. References. Intermediate System-to-Intermediate System Protocol www.cisco.com CNAP presentation Presentation of P. Paluch (fri.utc.sk). Reasons why to u ses IS-IS Routing. Large ISPs Stable protocol

shae
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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The IS-IS Protocol SAvPS Genci

  2. References • Intermediate System-to-Intermediate System Protocol www.cisco.com • CNAP presentation • Presentation of P. Paluch (fri.utc.sk)

  3. Reasons why to uses IS-IS Routing Large ISPs • Stable protocol • Originally deployed by ISPs because US government mandated internet support of OSI and IP

  4. Úvod do OSI sietí • Na prelome 70. a 80. rokov 20. storočia sa vývoj uberaldvomi smermi: • US Department of Defense vyvíjal tzv. Network Control Program,ktorý bol neskôr nahradený súčasnou sadou protokolov TCP/IP • ISO sa snažila vytvoriť a štandardizovať vlastnú sadu protokolov –tzv. OSI stack, ktorý zodpovedá známemu RM ISO OSI • Zatiaľčo pragmatici programujúci TCP/IPjednoduchosťou a prehľadnosťou protokolu uspeli, ISOsa zdržovala vytváraním formálnych, komplexných aabstraktných protokolov a rozhraní medzi nimi • Protokoly ISO sú pomerne komplikované, ich štandardizácia sa dlhýcas vliekla • ISO protokoly dodnes možno nájsť v sieťach telekomunikačnýchoperátorov, avšak masové nasadenie ISO protokolov nikdynenastalo

  5. Intro to OSI Networks - History

  6. Úvod do OSI sietí • Pre OSI siete boli navrhnuté niekolké smerovacie protokoly: • ES-IS: komunikácia medzi stanicou a jej bránou • IS-IS: komunikácia medzi routermi v jednom autonómnom systéme (v ISO terminológii „doména“) • IDRP: komunikácia medzi doménami (analóg BGP) • Vlastnosti IS-IS sa ukázali ako dobré a premyslené • IS-IS bol navrhovaný a funkcný skôr než OSPF a OSPF štartovalo ako lahký odvar IS-IS • Pri migrácii existujúcich OSI sietí na IP bolo vhodnejšie mat protokol, ktorý dokáže naraz slúžit aj pre OSI, aj pre IP • Do IS-IS boli v RFC 1195 dodefinované rozšírenia pre spoluprácu s IP svetom, sémantika protokolu však zostala

  7. ISO Protocol Suite

  8. ISO OSI Connectionless Network Service • OSI CLNS (Connectionless Network Service) is a network layer service similar to the IP service. • A CLNS entity communicates over Connectionless Network Protocol (CLNP) with its peer CLNS entity. • Routers are ISs, and hosts are End Systems (ESs). • ESs themselves have no routing information; • they discover ISs (routers) by listening to Intermediate System Hellos (ISHs) and sending traffic to any random router. • ESs send End System Hellos (ESHs); • they do not choose a designated router to handle all traffic, • optimal routing is accomplished via redirects

  9. CLNS Terminology

  10. Four OSI Routing Levels

  11. ISO Addressing • CLNS addresses that are used by routers are called network service access points (NSAPs) • NSAP addresses have a size from 8 to 20 bytes • NSAP address contains OSI address of the device and link to the higher layer process

  12. NSAP Address Formats

  13. ISO Address Structure

  14. Network Entity Title (NET Address) • NSAP addresses have a one-octet NSEL field that identifies a process on the device • NET addresses are NSAP addresses with an NSEL value of 0

  15. Example

  16. Continue – Paluch sl. 11

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  21. 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

  22. 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.

  23. 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.

  24. Four OSI Routing Levels

  25. 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.

  26. 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

  27. Advantages of Integrated IS-IS • Supports CLNP and IP • More extensible through TLV design

  28. 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.

  29. Comparison of Integrated IS-IS and OSPF The following table summarizes the differences between OSPF and integrated IS-IS.

  30. The IS-IS Protocol BSCI Module 4 Lesson 3 Configuring Basic Integrated IS-IS

  31. OSI Area Routing: Building an OSI Forwarding Database (Routing Table) • When databases are synchronized, Dijkstra’s algorithm (SPF) is run on the LSDB to calculate the SPF tree. • The shortest path to the destination is the lowest total sum of metrics. • Separate route calculations are made for Level 1 and Level 2 routes in Level 1-2 routers. • Best paths are placed in the OSI forwarding database (CLNS routing table).

  32. Building an IP Routing Table • Partial Route Calculation (PRC) is run to calculate reachability. • Since IP and ES are represented as leaf objects, they donot participate in SPF. • Best paths are placed in the IP routing table following IP preferential rules. • They appear as Level 1 or Level 2 IP routes.

  33. Integrated IS-IS Configuration Steps • Define areas, prepare addressing plan (NETs) for routers, and determine interfaces. • Enable IS-IS on the router. • Configure the NET. • Enable Integrated IS-IS on the appropriate interfaces. Do not forget interfaces to stub IP networks, such as loopback interfaces (although there are no CLNS neighbors there). • These are each explained in the next few slides.

  34. Integrated IS-IS Routing Three Basic Commands

  35. Step 1: Define Area and Addressing • Area determined by NET prefix: • Assign to support two-level hierarchy. • Addressing: • IP:Plan to support summarization. • CLNS: Prefix denotes area. System ID must be unique.

  36. Step 2: Enable IS-IS on the Router router(config)# router isis [area-tag] • Enable the IS-IS routing protocol. • area-tag– name for a process • When routing of CLNS packets is also needed, use the clns routing command.

  37. Step 3: Configure the NET Router(config-router)# net network-entity-title • Configure an IS-IS NET address for the routing process.

  38. Step 4: Enable Integrated IS-IS router(config-if)# ip router isis [area-tag] • Includes an interface in an IS-IS routing process

  39. Simple Integrated IS-IS Example The configured router acts as an IP-only Level 1-2 router. interface FastEthernet0/0 ip address 10.1.1.2 255.255.255.0 ip router isis ! interface Serial 0/0/1 ip address 10.2.2.2 255.255.255.0 ip router isis ! <output omitted> router isis net 49.0001.0000.0000.0002.00

  40. Change IS-IS Router Level Router(config-router)# is-type {level-1 | level-1-2 | level-2-only} • Configure the IS-IS level globally on a router; the default is level 1-2.

  41. Change IS-IS Interface Level Router(config-if)# isis circuit-type {level-1 | level-1-2 | level-2-only} • Configure the type of adjacency on an interface; the default is Level 1-2.

  42. Change IS-IS Metric Router(config-if)# isis metric metric [delay-metric[expense-metric [error-metric]]]{level-1 | level-2} • Configure the metric for an interface; the default is 10. • Metric value is from 1 to 63. Router(config-router)# metric default-value{level-1 | level-2} • Alternately, configure the metric globally for all interfaces.

  43. Example: Tuning IS-IS Configuration • Change router type on R1 and R3 • Change interface levels on R2 • Change metric on S0/0/1

  44. IP Summarization Router(config-router)# summary-address address mask [level-1 | level-2 |level-1-2][tag tag-number] [metric metric-value] • Creates summary • Default is Level 2 Example: P3R1(config-router)# summary-address 10.3.2.0 255.255.254.0 level-1-2 • Summarizes 10.3.2.0/23 into Level 1-2

  45. Example: Is Integrated IS-IS Running? R2#show ip protocols Routing Protocol is "isis" Invalid after 0 seconds, hold down 0, flushed after 0 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: isis Address Summarization: None Maximum path: 4 Routing for Networks: FastEthernet0/0 Loopback0 Serial0/0/1 Routing Information Sources: Gateway Distance Last Update 10.10.10.10 115 00:00:02 10.30.30.30 115 00:00:03 Distance: (default is 115) • Displays the parameters and current state of the active routing protocol processes

  46. Example: Are There Any IP Routes? router# show ip route [address [mask]] | [protocol [process-id]] R2#show ip route isis 10.0.0.0/24 is subnetted, 5 subnets i L2 10.30.30.0 [115/45] via 10.2.2.3, Serial0/0/1 i L1 10.10.10.0 [115/20] via 10.1.1.1, FastEthernet0/0 R2# • Displays the current state of the routing table

  47. TroubleshootingCommands: CLNS Router# show clns • Displays information about the CLNS network Router# show clns [area-tag] protocol • Lists the protocol-specific information Router# show clns interface [typenumber] • Lists the CLNS-specific information about each interface Router# show clns [area-tag] neighbors [type number] [detail] • Displays both ES and IS neighbors

  48. TroubleshootingCommands: CLNS and IS-IS Router# show isis [area-tag] route • DisplaysIS-IS Level 1 routing table (system IDs) Router# show clns route [nsap] • Displays IS-IS routing table (areas) Router# show isis [area-tag] database • Displaysthe IS-IS LSDB Router# show isis [area-tag] topology • Displays IS-IS least-cost paths to destinations

  49. Example: OSI Intra-Area andInterarea Routing Routing in a Two-Level Area Structure

More Related