1. CCNP1: Advanced Routing v3.0 CISCO NETWORKING ACADEMY PROGRAM Chapter 2 – Single Area OSPF OSPF Link State Routing Single Area and Multiarea OSPF

2. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Identify Distance Vector & Link State Routing Characteristics Periodic updates Topology changes trigger updates Updates sent to neighbours Updates contain changes only Updates contain entire routing table Increased memory & processing requirements Updates consume significant bandwidth Rapid convergence Updates sent to all routers Support CIDR/VLSM Slow convergence

3. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Identify Distance Vector & Link State Routing Characteristics Periodic updates Topology changes trigger updates Updates sent to neighbours Updates contain changes only Updates contain entire routing table Increased memory & processing requirements Updates consume significant bandwidth Rapid convergence Updates sent to all routers Support CIDR/VLSM Slow convergence

4. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Summary of Link State Features Responds quickly to network changes Use ‘hellos’ to discover and create neighbors Send updates when a there has been a change in the network topology Updates contain changes not whole routing table Calculates shortest path to each route in the network from a separate topology table

5. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Link State Operation Routers are aware of directly connected networks known as ‘links’ Routers send ‘hellos’ to discover neighbors Routers send Link State Advertisements (LSAs) to other routers informing them of their links All routers add Link State Advertisements to their topological database (topology table) Shortest Path algorithm calculates best route to each network When link states change, LSA update are sent to all routers which recalculate their routes

6. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Topological Database Every router advertises directly connected networks via Link State Advertisements Every router has it’s own view of the network – it builds a ‘topological database’ Router A is aware of 2 paths to 192.168.157.0 – this provides redundancy should one of the routers fail

7. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Evaluation of Link State Routing

8. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Review – Link State & Distance Vector

9. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Overview Preferred to RIP on larger networks Open Standard - IETF RFC 2328 Link State routing protocol Interior Gateway Protocol for Autonomous systems Metric based on bandwidth - Cost Supports VLSM OSFP can use ‘areas’ to allow hierarchical design – Multiarea OSPF

10. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Key Words Adjacencies database Directly connected routers Topological Database Routes to every network Routing table –Best path to each network (chosen from topological database) Designated Router A router elected by all others to represent the network area (multi-access networks only) Area 0 backbone

11. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Packet Types Type 1 – Hello –Establishes and Maintains adjacency info w/ neighbors Type 2 – Database description packet (DBD) –Describes the contents of an OSPF router’s link-state database Type 3 – Link State Request –Requests specific pieces of a routers link-state database Type 4 – Link State Update (LSUs) –Transports link-state advertisements (LSAs) to neighbor routers Type 5 – Link-state acknowledgement (LSAKs) –Acknowledges receipt of a neighbor’s LSA

12. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Hello Protocol

13. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Designated Router/Backup DR All LSA sent to DR/BDR instead of to every single router Reduces overhead of LSA updates Standard on multi-access networks DR is single point of failure – solution is BDR

14. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF DR/BDR Once a DR is established, a new router with a higher priority or router ID will NOT become the DR or BDR. If DR fails, BDR takes over as DR and selection process for new BDR begins.

15. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Backup Designated Router Listens, but doesn’t act. If LSA is sent, BDR sets a timer. If timer expires before it sees the reply from the DR, it becomes the DR and takes over the update process. The process for a new BDR begins.

16. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF DR/BDR selection To suit the topology used the network administrator will want to choose DR/BDR DR/BDR election based on OSPF priority Highest priority=DR 2 nd highest priority=BDR Priority of 0 = DROTHER (ensures will not be DR) Default priority = 1 Router(config-if)#ip ospf priority number Router#show ip ospf interface type number

17. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Loopback Address For OSPF to function there must always be an active interface Physical interfaces e.g. serial/Ethernet may not always be active – routing would fail Configure virtual “loopback” interface as solution Subnet mask will always be 255.255.255.255 Router(config)#interface loopback number Router(config-if)#ip address ip-address subnet-mask

18. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Drothers – All Other OSPF Routers All other routers, DROTHER, establish adjacencies with DR and BDR only. LSAs are multicast to DR and BDR only – (224.0.0.6 - all DR routers) DR sends LSA to all adjacent neighbors –(224.0.0.5 - all OSPF routers)

19. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF basic commands Router(config)#router ospf process-id Router(config-router)#network address wildcard-mask area area-id EXAMPLE Router(config)#router ospf 2 Router(config-router)#network 172.16.10.0 0.0.0.255 area 2 NOTES process-id can be a value between 0 and 65,535 Wildcard mask NOT subnet mask used with network command

20. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Basic OSPF Configuration

21. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring OSPF Authentication within a Single Area Rtr(config)# router ospf process-id Rtr(config-router)#network address wildcard-mask area area-id Rtr(config-router)# area area authentication [message-digest] Rtr(config)# interface type slot/port Rtr(config-if)# ip ospf priority RTB(config-if)# ip ospf cost cost Rtr(config-if)# ip ospf hello-interval seconds Rtr(config-if)# ip ospf dead-interval seconds Rtr(config-if)# ip ospf message-digest-key key-id md5 [encryption-type] password

22. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Steps to OSPF Operation 1. Establishing router adjacencies 2. Electing DR and BDR 3. Discovering Routes 4. Choosing Routes 5. Maintaining Routing Information

23. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Router States down init 2 way exstart exchange loading full Good neighbors, no LSA sharing. Sharing route via LSAs.

24. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Reaching 2-Way

25. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Electing a DR/BDR

26. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 1.Establishing Adjacencies An OSPF router tries to form an adjacency with at least one neighbor for each IP network it’s connected to.

27. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 2.Electing a DR and BDR On point-to-point links adjacencies are established with all neighbors, because there is only one neighbor. On multi-access networks,OSPF elects a DR and BDR to limit the number of adjacencies. –Reduce routing update traffic

28. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 3.Discovering Routes EXSTART state - prepare for initial database exchange of Database Description Packets (DBDs) master/slave relationship decided (higher router id) EXCHANGE state - routers exchange one or more DBDs (Database Description) packets, which is a summary of the link-state database –send LSAcks to verify –compares DBD with its own database

29. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 3.Discovering Routes LOADING STATE - When a slave router receives a DBD it: –Acknowledges receipt of the DBD by sending an LSAck –Compares the information it received with the information it has by checking the LSA sequence number –If the DBD has a more up-to-date link-state entry, the slave router sends a link state request (LSR) to the master –The master responds with a link state update (LSU).

30. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 3.Discovering Routes When all LSRs have been satisfied for a given router, the adjacent routers are considered to be synchronized and in a FULL STATE. At this point all routers within the network should have identical link-state databases.

31. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 4.Choosing Routes OSPF bases routing metrics on cost. Cisco routers, cost = 10 8 /BW BW is the configured bandwidth for an interface and may be changed using the ip ospf cost command. The bandwidth command can also be used to change the bandwidth metric on an interface. ip ospf cost is used when converting the metric between routers from different vendors.

32. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Choosing Routes SPF, Shortest Path First calculations use the Dijkstra algorithm, placing itself as the root and creating a “tree diagram” of the network

33. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF 5.Maintaining Routing Info Flooding process When there is a state change in one of the connected links, as soon as the router learns of this change it floods it to all adjacent neighbors (224.0.0.6 - all DR/BDRs). Only the changed link information is flooded, not the entire database. DR sends LSU (LSA) to others on the network, area (224.0.0.5 all SPF routers) Router which receives LSU updates links-state database, computes the SPF algorithm, and generates a new routing table LSAs are aged at 30 minutes and flooded every 30 minutes

34. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Additional Configuration Network administrators can also configure: LSA update authentication OSPF Priority at the interface ‘Hello’ & ‘Dead’ interval timers Default route to routers outside the area/autonomous system

35. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring OSPF Loopback Address and Router Priority

36. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Setting OSPF Priority The priorities can be set to any value from 0 to 255. A value of 0 prevents that router from being elected. A router with the highest OSPF priority will win the election for DR.

37. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Modifying OSPF Cost Metric

38. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring OSPF Authentication The encryption setting of 7 is Cisco proprietary and will not work properly. Use 5 for MD5 hash instead.

39. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring timers Rtr(config-if)# ip ospf hello-interval seconds Rtr(config-if)# ip ospf dead-interval seconds For OSPF routers to be able to exchange information, the must have the same hello intervals and dead intervals. By default, the hello interval is 4 times the dead interval, so the a router has four chances to send a hello packet being declared dead. (not required) Defaults On broadcast networks hello interval = 10 seconds, dead interval 40 seconds. On non-broadcast networks hello interval = 30 seconds, dead interval 120 seconds.

40. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring OSPF Timers Example

41. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF - Propagating a Default Route Default routes are used if the destination network is not in the routing table. The border router (Router B) is the default router. Router B must use the command ‘default-information originate’ to propagate default information to the rest of the OSPF network.

42. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Default Router Example Router(config)# int s0/0 Router(config-if)# ip address 172.16.16.2 255.255.255.252 Router(config-if)# no shut Router(config-if)# exit Router(config)# ip route 0.0.0.0 0.0.0.0 172.16.16.1 Router(config)# router ospf 1 Router(config-router)# network 192.168.1.0 0.0.0.3 area 0 Router(config-router)# network 192.168.1.128 0.0.0.63 area 0 Router(config-router)# default-information originate Notice the 172. network is not included in the OSPF configuration because you are not running OSPF to the Internet provider.

43. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Areas Every OSPF router must belong to at least one area Every OSPF network must have an Area 0 (backbone area) All other Areas should “touch” Area 0 –There are exceptions to this rule Routers in the same area have the same link- state information

44. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF uses Areas Hierarchical routing enables you to separate large internetworks (autonomous system) into smaller internetworks that are called areas. With this technique, routing still occurs between the areas (called inter-area routing), but many of the smaller internal routing operations, such as recalculating the database, are restricted within an area.

45. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Areas

46. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Router Types

47. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Router Types Internal Internal: Routers with all their interfaces within the same area Backbone Backbone: Routers with at least one interface connected to area 0 ASBR ASBR: (Autonomous System Boundary Router): Routers that have at least one interface connected to an external internetwork (another autonomous system) ABR ABR: (Area Border Router): Routers with interfaces attached to multiple areas.

48. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Area Types Standard Backbone Stub –Stub –Totally Stubby Area (TSA) –Not-so-stubby-area (NSSA)

49. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Area Types

50. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Stub, Totally Stubby and Not-so-stubby A stub area does not accept information about routes external to the AS A totally stubby area, which is a Cisco specific feature, blocks external Type 5 LSAs and summary, Type 3 and Type 4, LSAs from entering the area. An NSSA does not allow Type 5 LSAs but does allow Type 7 LSAs, which can carry external routing information and be flooded throughout the NSSA.

51. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Area Types Key difference between area types: –How they handle external routes (E1 and E2). –External routes are injected into OSPF by ASBR –Type 1 (E1): cost metric increments as route is passed through OSPF domain –Type 2 (E2): cost metric remains the same as route is passed through OSPF domain

52. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF LSA Types

53. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF LSA Types (con’t) Type 6MOSPF (Multicast OSPF) Not supported by Cisco. –MOSPF enhances OSPF by letting routers use their link-state databases to build multicast distribution trees for the forwarding of multicast traffic.

54. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF LSA Types (con’t) Type 7 NSSA External Link Entry –Originated by an ASBR connected to an NSSA. Type 7 messages can be flooded throughout NSSAs and translated into LSA Type 5 messages by ABRs. Routes learned via Type-7 LSAs are denoted by either a “N1” or and “N2” in the routing table. (Compare to E1 and E2).

55. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Multi-area Example ABR ASBR RIP

56. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Stub Example ABR ASBR No Type 5 LSAs Route to 0.0.0.0/0 via RTB

57. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Totally Stubby Example ABR ASBR No Type 3, 4, or 5 LSAs Route to 0.0.0.0/0 via RTB (no more IA routes) Totally Stubby Area no summary

58. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NSSA Example ABR ASBR No Type 5 LSAs Type 7 okay

59. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NSSA Example ABR ASBR No Type 3, 4 or 5 LSAs Type 7 okay no summary

60. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Configuring Summary Routes Interarea route summarization (at ABR) Router(config-router)# area [area-id] range [address] [mask] Router(config-router)# area 1 range 192.168.16.0 255.255.252.0 External route summarization (at ASBR) Router(config-router)# summary-address [address] [mask] Router(config-router)# summary-address 200.9.0.0 255.255.0.0

61. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Virtual Links A virtual link has the following two requirements: –It must be established between two routers that share a common area. –One of these two routers must be connected to the backbone.

62. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Virtual Links RTA(config)#router ospf 1 RTA(config-router)#network 192.168.0.0 0.0.0.3 area 51 RTA(config-router)#network 192.168.1.0 0.0.0.3 area 3 RTA(config-router)#area 3 virtual-link 10.0.0.1... RTB(config)#router ospf 1 RTB(config-router)#network 192.168.1.0 0.0.0.3 area 3 RTB(config-router)#network 192.168.2.0 0.0.0.3 area 0 RTB(config-router)#area 3 virtual-link 10.0.0.2

63. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Why Virtual Link? Temporary fix when two existing OSPF networks merge (company merger, etc.) Backup path

64. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Common OSPF Configuration Issues

65. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF OSPF Interface Information Rtr# show ip ospf interface Ethernet0 is up, line protocol is up Internet Address 206.202.2.1/24, Area 1 Process ID 1, Router ID 1.2.202.206, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State BDR, Priority 1 Designated Router (ID) 2.2.202.206, Interface address 206.202.2.2 Backup Designated router (ID) 1.2.202.206, Interface address 206.202.2.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:00 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 2.2.202.206 (Designated Router) Suppress hello for 0 neighbor(s) Serial0 is up, line protocol is up Internet Address 206.202.1.2/24, Area 1 Process ID 1, Router ID 1.2.202.206, Network Type POINT_TO_POINT, Cost: 64 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 2.0.202.206 Suppress hello for 0 neighbor(s)

66. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Verifying OSPF Configuration show ip protocol show ip route show ip ospf interface shop ip ospf show ip ospf neighbor detail show ip ospf database

67. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF The debug and clear Commands for OSPF Verification

68. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NBMA Non-Broadcast Multi-access Access Networks. –Frame Relay –X.25 Without broadcasts and multicasts, DR/BDR election is problematic

69. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Network Types Cisco routers can treat NBMA interfaces using any of the following: Non-Broadcast OSPF is aware that multicast packets cannot be sent over the interface and sends OSPF packets directly to neighbors using unicast addresses. DR and BDR are not elected by default DR represent the NBMA cloud as a transit network, using network LSAs Suitable only for when the VCs are fully meshed Broadcast OSPF treats the interface as belonging to a broadcast segment, thus using multicasts to send OSPF packets. DR and BDR are elected Suitable only for when the VCs are fully meshed. NBMA Networks and OSPF

70. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF Network Types Cisco routers can treat NBMA interfaces using any of the following: Point-to-multipoint OSPF treats the interface as a placeholder for a set of point-to-point adjacencies. No DR/BDR is elected Very much like point-to-point interfaces, except that every router announces a host route to its own IP address. Point-to-point OSPF treats the interface as a set of point-to-point adjacencies No DR/BDR is elected. NBMA Point-to-Point and Multipoint Networks

71. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NBMA Solution Full meshFull mesh Full Mesh network is on one subnet The OSPF neighbor command tells a router about the IP addresses of its neighbors so that it can exchange routing information without multicasts.

72. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NBMA Solution Point-to-pointPoint-to-point uses subinterfaces Point-to-point networks are all on different subnets

73. CCNP1: Advanced Routing CISCO NETWORKING ACADEMY PROGRAM Chapter 6 –OSPF NMBA Solution Point-to-multipointPoint-to-multipoint Point-to-Multipoint network is on one subnet The broadcast keyword permits the router to send broadcasts by way of the specified DLCI to the mapped neighbor or neighbors.