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IS-IS Intermediate System-to-Intermediate System

IS-IS Intermediate System-to-Intermediate System. Rick Graziani Cabrillo College graziani@cabrillo.edu Fall 2009. Sources. Sources used in creating this IS-IS presentation: Cisco Online curriculum, CCNP 1 version 3.0 IS-IS Network Design Solutions, Cisco Press Very Good Reference

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IS-IS Intermediate System-to-Intermediate System

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  1. IS-ISIntermediate System-to-Intermediate System Rick Graziani Cabrillo College graziani@cabrillo.edu Fall 2009

  2. Sources • Sources used in creating this IS-IS presentation: • Cisco Online curriculum, CCNP 1 version 3.0 • IS-IS Network Design Solutions, Cisco Press • Very Good Reference • CCNP Self-Study (BSCI), Cisco Press • Routing TCP/IP Volume I by Jeff Doyle Rick Graziani graziani@cabrillo.edu

  3. IS-IS versus OSPF “IS-IS is exactly the same as OSPF only completely different.”

  4. IS-IS versus OSPF • OSPF – discussed in CCNA and CCNP (Single Area and Multi-Area) • The following slides show terminology differences between IS-IS and OSPF. • Similar to the differences between Spanish and Italian. • Suggestion: Put the following on the board. Rick Graziani graziani@cabrillo.edu

  5. IS-IS versus OSPF - Terminology Rick Graziani graziani@cabrillo.edu

  6. IS-IS versus OSPF - Terminology Rick Graziani graziani@cabrillo.edu

  7. IS-IS versus OSPF – ISs (Routers) Rick Graziani graziani@cabrillo.edu

  8. IS-IS versus OSPF - Timers Rick Graziani graziani@cabrillo.edu

  9. History of IS-IS and OSPF Just like the MacIntosh versus Windows debate

  10. History of IS-IS and OSPF http://www.nanog.org • 1985 • Originally called DECnet Phase V • 1987 • IS-IS (from DEC) selected by ANSI as OSI intradomain protocol (CLNP only) • 1988 • NSFnet deployed, IGP based on early IS-IS draft • OSPF work begins, loosely based on IS-IS mechanisms • IP extensions to IS-IS defined • 1989 • OSPF v.1 RFC published • IS-IS becomes ISO proposed standard • Public bickering ensues--OSPF and IS-IS are blessed as equals by IETF, with OSPF somewhat more equal • Private cooperation improves both protocols • 1990 • Dual-mode IS-IS RFC published Rick Graziani graziani@cabrillo.edu

  11. History of IS-IS and OSPF http://www.nanog.org • 1991 • OSPF v.2 RFC published • Cisco ships OSI-only IS-IS • 1992 • Cisco ships dual IS-IS • Lots of OSPF deployed, but very little IS-IS • 1993 • Novell publishes NLSP (IPX IS-IS knockoff) • 1994 • Large ISPs need an IGP; IS-IS is recommended due to recent rewrite and OSPF field experience (and to lesser extent, NSF CLNP mandate) • 1995 • ISPs begin deployment of IS-IS, Cisco implementation firms up, protocol starts to become popular in niche Rick Graziani graziani@cabrillo.edu

  12. History of IS-IS and OSPF http://www.nanog.org • 1996-1998 • IS-IS niche popularity continues to grow (some ISPs switch to it from OSPF) • IS-IS becomes barrier to entry for router vendors targeting large ISPs • Juniper and other vendors ship IS-IS capable routers • 1999-present • Extensions continue for both protocols Rick Graziani graziani@cabrillo.edu

  13. Who uses IS-IS? • IS-IS is popular amongst telcos and large ISPs (at least in U.S.). • A Tier 1 carrier is a telco or ISP that is at the top of the telecommunications peering and settlements food chain. • Tier 1 operators typically have operations in more than one country • Tier 1 operators own and operate their own physical networks, and either own or part-own their international submarine cable links. • Example of Tier 1 carriers (not necessarily IS-IS users): • AT&T • Global Crossing • Level 3 • NTT/Verio • Qwest • Sprint • Verizon Business (UUNET) Rick Graziani graziani@cabrillo.edu

  14. Introduction to IS-IS Protocol Routers Areas

  15. OSI: Two Network Services, Two Network Protocols • CMNS (Connection Mode Network Service) – Requires establishment of a path between transport layer entites. • CONP (Connection-Oriented Network Protocol) – OSI network layer protocol that carries upper layer data over connection-oriented links. • CLNS (Connectionless Network Service) – Performs datagram support, does not require circuit to be established • CLNP (Connectionless Network Protocol) – OSI network layer protocol that carries upper layer data over connectionless links. (Similar to IP) Rick Graziani graziani@cabrillo.edu

  16. IS-IS Protocol Options • IS-IS (ISO 10589) • Dynamic link state routing protocol used in an ISO CLNS environment. • Integrated IS-IS (RFC 1195) • IS-IS for mixed ISO CLNS and IP environments. • Either: • Purely ISO • Purely IP (CCNP 1) • Both Rick Graziani graziani@cabrillo.edu

  17. OSI Routing Protocols: ES-IS and IS-IS ES-IS • Analogous to Address Resolution Protocol (ARP) in IP • Not technically a routing protocol • Sometimes referred to as Level 0 routing. • ESs (hosts) discover nearest IS (router) by listening to IS Hello (ISH) packets • ISs (routers) know which hosts are on their subnetwork by listening to ES Hello (ESH) packets. • Not applicable for IP networks ISH ESH Rick Graziani graziani@cabrillo.edu

  18. OSI Routing Protocols: ES-IS and IS-IS IS-IS • OSI distinguishes between Level 1, Level 2, and Level 3 routing. • Level 1 Routing • If DA is an ES on another subnetwork in the same area, the IS knows the correct route and forwards packet appropriately. • Level 2 Routing • If DA is an ES on another area, the Level 1 IS sends the packet to the nearest Level 2 IS. (coming) • Level 3 Routing is between separate domains. • Pure CLNS environment IDRP or ISO-IGRP can be used, in IP, BGP is used. (Not applicable to CCNP) Boundary areas in IS-IS exists on a link between routers and not on a router itself as in OSPF. These routers should be entirely in Area 1 and Area 2. Rick Graziani graziani@cabrillo.edu

  19. IS-IS Areas IS-IS Routers: • Level 1 IS (L1 IS, router) • Analogous to OSPF Internal non-backbone router (Totally Stubby) • Responsible for only routing to ESs inside an area. • Level 2 IS (L2 IS, router) • Analogous to OSPF Internal Backbone router • Responsible for routing between areas • Level 1 and Level 2 IS (L1-L2 IS, router) • Analogous to OSPF ABR router • Participate in both L1 intra-area routing and L2 inter-area routing. Rick Graziani graziani@cabrillo.edu

  20. Level 1 Router • Level 1 IS (L1 IS, router) • Analogous to OSPF Internal non-backbone router (Totally Stubby) • Responsible for only routing to ESs inside an area. • Level 1 routers maintain the Level 1 database for the area and exit points to neighboring areas. Rick Graziani graziani@cabrillo.edu

  21. Level 2 Router • Level 2 IS (L2 IS, router) • Analogous to OSPF Internal Backbone router • Responsible for routing between areas • Also referred to as area routers. • Interconnects the Level 1 areas • Store separate database of only inter-area topology Rick Graziani graziani@cabrillo.edu

  22. Level 1 – Level 2Router • Level 1 and Level 2 IS (L1-L2 IS, router) • Analogous to OSPF ABR router • Participate in both L1 intra-area routing and L2 inter-area routing. • Maintain both Level 1 and Level 2 LSDB • Support Level 1 function communicating with other Level 1 routers in their area • Inform other Level 1 routers that they are the exit point (default route) from the area. • Support Level 2 function communicating with the rest of the backbone path. Rick Graziani graziani@cabrillo.edu

  23. IS-IS Backbone • IS-IS does not share the concept of a backbone area 0 with OSPF. • IS-IS backbone a set of distinct areas interconnected by a chain of Level 2 routers, weaving their way through and between the Level 1 Areas. • The IS-IS backbone (path) consists of a contiguous set of Level 1-2 and Level 2 routers. • Where is the backbone (path)? Rick Graziani graziani@cabrillo.edu

  24. OSI Addressing NSAP (Area, System ID, NSEL) SNAP

  25. OSI Addressing • IS-IS uses OSInetwork layer addressing • In IP only networks used to identify the router (IS) • A variety of NSAP formats exist, which we will not go into. • Represented in hexadecimal (up to 40 hex digits) • Cisco format: Area – System ID – NSEL (always 00 on ISs) 49.0001.2222.2222.2222.00 NSAP Rick Graziani graziani@cabrillo.edu

  26. NSAPs • Format of the Cisco NSAP address consists of three parts. • Area address • System ID • NSAP selector byte • Area address is a variable length field • The system ID is the ES or IS identifier in an area, similar to theOSPF router ID. • The system ID has a fixed length of six bytes as engineered in the Cisco IOS. • The NSAP selector byte is a service identifier. • Analogous to that of a port or socket in TCP/IP. Rick Graziani graziani@cabrillo.edu

  27. Do I have to know this, I am only routing IP? • Even in IP only networks, IS-IS uses OSI addresses: • Identify the router (IS) • Build the topology table • Build the SPF tree • LSPs • Hello and other PDUs Rick Graziani graziani@cabrillo.edu

  28. NSAPs – Cisco Format Area • Addresses starting with 49 (AFI=49) are considered private IP address, analogous to RFC 1918. • Routed by IS-IS • Should not be advertised to other CLNS networks (outside this IS-IS domain) • Additional 2 bytes (0001) added for the area ID • All routers in the same are must have the same area address Area – System ID – NSEL 49.0001.2222.2222.2222.00 Rick Graziani graziani@cabrillo.edu

  29. NSAPs – Cisco Format System ID • Cisco fixes the System ID at 6 bytes. • Customary to use one of the following: • MAC address from the router • IP address of loopback interface • 192.168.111.3 -> 192.168.111.003 -> 1921.6811.1003 • Each device (IS and ES) must have a unique System ID within the area. (Recommended to make them unique within the domain.) Area – System ID – NSEL 49.0001.2222.2222.2222.00 Rick Graziani graziani@cabrillo.edu

  30. NSAPs – Cisco Format NSEL (NSAP Selector) • NSEL is a service identifier. • Loosely equivalent to that of a port or socket in TCP/IP. • Not used in routing decisions. NET (Network Entity Title) • When NSEL = 00, it identifies the device itself, the network level address. • The NSAP with a NSEL = 00 is known as a Network Entity Title (NET) • A NET is an NSAP with the NSEL set to (00) Area – System ID – NSEL 49.0001.2222.2222.2222.00 Rick Graziani graziani@cabrillo.edu

  31. NSAP (NETs) Area – System ID – NSEL 49.0001.2222.2222.2222.00 Example 1: NSAP 47.0001.aaaa.bbbb.cccc.00 • Area ID is: • 47.0001 • System ID is: • aaaa.bbbb.cccc • NSAP selector byte is: • 00 Example 2: NSAP 39.0f01.0002.0000.0c00.1111.00 • Area ID is: • 39.0f01.0002 • System ID is: • 0000.0c00.1111 • NSAP selector byte is: • 00 Other Examples Rick Graziani graziani@cabrillo.edu

  32. Configuring IS-IS (so far) Area 49.0001 • ip router isis: IS-IS must be enabled on the interface • Note: IS-IS routing cannot be enabled on an interface until an IP address has been configured on the interface. • IOS: Cisco IOS 12.2(12) with Enterprise Plus (16 MB Flash/48 MB RAM) or Enter Plus IPSec56 (16 MB Flash/64 MB RAM) SanJose1 interface FastEthernet0/0 ip address 172.16.0.1 255.255.255.0 ip router isis isis priority 100 router isis net 49.0001.1111.1111.1111.00 SanJose2 interface FastEthernet0/0 ip address 172.16.0.2 255.255.255.0 ip router isis router isis net 49.0001.2222.2222.2222.00 Area . System ID . NSEL SanJose3 interface FastEthernet0/0 ip address 172.16.0.3 255.255.255.0 ip router isis router isis net 49.0001.3333.3333.3333.00 Rick Graziani graziani@cabrillo.edu

  33. Configuring IS-IS (so far) Area 49.0001 • To display both ES and IS neighbors. • SNPA (Subnetwork Point of Attachment) address is the interface circuit ID. • Ethernet: MAC address of the remote router. • Serial, would show encapsulation, I.e. HDLC • Type: Cisco routers default to L1-L2 type routers. • We will see how to change this in a moment. Rick Graziani graziani@cabrillo.edu

  34. IS-IS Adjacencies Are we half way yet?

  35. Hello Messages • IS-IS uses Hello PDUs to establish adjacencies with other routers (ISs) and ESs. • IS-IS has three types of Hello PDUs: • ESH, sent by ES to an IS • ISH, sent by IS to an ES • IIH, used between two ISs (CCNP) Rick Graziani graziani@cabrillo.edu

  36. Neighbors and Adjacencies • IS-IS discover neighbors and forms adjacencies using IS-IS Hello PDUs. • Transmitted every 10 seconds • Can be changed using the interface command, is hello-interval • Hold time defaults to 3 times the Hello time (30 seconds), before declaring a neighbor dead. • Changed using the interface command is hello-multiplier • Default is 3 Rick Graziani graziani@cabrillo.edu

  37. LAN Representation and Adjacencies • Similar to the DR in OSPF… • DIS (Designated IS) is elected to generate the LSP (Link State Packet, ie. LSA) representing the virtual router connecting all attached routers to a star-shaped topology • LAN uses a virtual node called pseudonode. • Represents the LAN • Sent by the DIS DIS Rick Graziani graziani@cabrillo.edu

  38. LAN Representation and Adjacencies • Election of DIS: • Router with highest priority (Cisco default is 64) • Router with highest MAC address • No “BDR” • No way to make a router ineligible from being DIS (no OSPF priority 0) • New router (IS) can cause a new election, unlike OSPF • Periodically broadcasts CSNPs (OSPF DBD) every 10 seconds DIS Rick Graziani graziani@cabrillo.edu

  39. Configuring IS-IS (so far) DIS Area 49.0001 • isis priority: Sets DIS priority on a LAN interface, default 64 SanJose1 interface FastEthernet0/0 ip address 172.16.0.1 255.255.255.0 ip router isis isis priority 100 router isis net 49.0001.1111.1111.1111.00 SanJose2 interface FastEthernet0/0 ip address 172.16.0.2 255.255.255.0 ip router isis router isis net 49.0001.2222.2222.2222.00 Area . System ID . NSEL SanJose3 interface FastEthernet0/0 ip address 172.16.0.3 255.255.255.0 ip router isis router isis net 49.0001.3333.3333.3333.00 Rick Graziani graziani@cabrillo.edu

  40. Adjacencies • L1 routers form L1 adjacencies with L1 and L1-L2 routers in their area. • L2 routers form L2 adjacencies with L2 and L1-L2 routers in their area or another area. • L1 router does not form an adjacency with an L2 router LAN Adjacencies Rick Graziani graziani@cabrillo.edu

  41. Adjacencies • What are the adjacencies? L1? L2? L1L2? None? • The adjacencies also determine what type of routes the IS (router) will have in its routing table. • L1 – Intra-area routes (routes only within that area) • L2 – Inter-area routes (routes from other areas) • Or both Rick Graziani graziani@cabrillo.edu

  42. Adjacencies • For an adjacency to be formed and maintained, routers must agree on: • If they are both Level 1, them must be in the same area • The System ID must be unique to each router. • The Hello timers do not have to match. Rick Graziani graziani@cabrillo.edu

  43. Metric and Calculate the Shortest Path • Four types of metrics: • Default – Cisco only supports this metric. • Delay • Expense • Error • Each metric expressed as an integer between 0 and 63. Rick Graziani graziani@cabrillo.edu

  44. Metric • Cisco assigns a default metric of 10 to every interface regardless of interface type. • Total cost of any route = sum of metrics of the outgoing interfaces. • By default, IS-IS metric becomes a simple measure of hop count. • Interface command: isis metric changes the default value. Rick Graziani graziani@cabrillo.edu

  45. Multi-Area IS-IS Example

  46. Note: ip router isis command must be added not only to transit interfaces but also to interfaces connected to stub networks whose IP addresses should be advertised by IS-IS. Levels L1L2 • is-type {level-1 | level-1-2 | level-2-only} SanJose1 interface FastEthernet0/1 ip address 192.168.10.1 255.255.255.252 ip router isis interface FastEthernet0/0 ip address 172.16.0.1 255.255.255.0 ip router isis interface Serial0/0 ip address 10.0.0.2 255.255.255.252 ip router isis router isis net 49.0001.1111.1111.1111.00 is-type level-1-2 SanJose2 interface FastEthernet0/0 ip address 172.16.0.2 255.255.255.0 ip router isis interface FastEthernet0/1 ip address 192.168.20.1 255.255.255.0 ip router isis router isis net 49.0001.2222.2222.2222.00 is-type level-1 L1 L2 Phoenix interface Serial0/0 ip address 10.0.0.1 255.255.255.252 ip router isis interface FastEthernet0/1 ip address 192.168.30.1 255.255.255.0 ip router isis router isis net 49.0002.3333.3333.3333.00 is-type level-2-only Rick Graziani graziani@cabrillo.edu

  47. show clns neigh L1L2 SanJose1#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol SanJose2 Fa0/0 0003.6be9.d480 Up 26 L1 IS-IS Phoenix Se0/0 *HDLC* Up 28 L2 IS-IS SanJose2#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol SanJose1 Fa0/0 0002.b9ee.5ee0 Up 4 L1 IS-IS Phoenix#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol SanJose1 Se0/0 *HDLC* Up 27 L2 IS-IS • System ID – Cisco IOS uses the hostname. • SNPA is the MAC of the remote router or HDLC on the serial link. • The Type is the is-type of the remote router. L1 L2 Rick Graziani graziani@cabrillo.edu

  48. show isis data L1L2 SanJose1#show isis database IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL SanJose1.00-00 * 0x00000005 0xDE15 916 1/0/0 SanJose1.01-00 * 0x00000003 0xBBFE 1165 0/0/0 SanJose2.00-00 0x00000006 0xBDFB 470 0/0/0 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL SanJose1.00-00 * 0x0000001B 0xAB48 914 0/0/0 SanJose1.01-00 * 0x0000001B 0x5526 480 0/0/0 Phoenix.00-00 0x0000001E 0xA3D3 912 0/0/0 Phoenix.01-00 0x00000002 0x54A6 826 0/0/0 • SanJose1 has a L1 LSDB and a L2 LSDB. L1 L2 Rick Graziani graziani@cabrillo.edu

  49. show isis data L1L2 SanJose2#show isis database IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL SanJose1.00-00 0x00000005 0xDE15 907 1/0/0 SanJose1.01-00 0x00000003 0xBBFE 1155 0/0/0 SanJose2.00-00 * 0x00000006 0xBDFB 464 0/0/0 Phoenix#show isis database IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL SanJose1.00-00 0x0000001B 0xAB48 893 0/0/0 SanJose1.01-00 0x0000001B 0x5526 459 0/0/0 SanJose2.00-00 0x00000024 0x2FD3 0 (932) 0/0/0 Phoenix.00-00 * 0x0000001E 0xA3D3 895 0/0/0 Phoenix.01-00 * 0x00000002 0x54A6 808 0/0/0 • SanJose2 only has a L1 LSDB. • Phoenix only has a L2 LSDB. L1 L2 Rick Graziani graziani@cabrillo.edu

  50. show ip route L1L2 SanJose1#show ip route i L2 192.168.30.0/24 [115/20] via 10.0.0.1, Serial0/0 C 192.168.10.0/24 is directly connected, FastEthernet0/1 172.16.0.0/24 is subnetted, 1 subnets C 172.16.0.0 is directly connected, FastEthernet0/0 i L1 192.168.20.0/24 [115/20] via 172.16.0.2, FastEthernet0/0 10.0.0.0/30 is subnetted, 1 subnets C 10.0.0.0 is directly connected, Serial0/0 • Because SanJose1 is an L1L2 router, it contains both: • L1 routes for Area 49.0001 and • L2 routes for the other area 49.0002. L1 L2 Rick Graziani graziani@cabrillo.edu

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