1. Configuring OSPF – Part 1 of 2 CIS 185 CCNP ROUTE Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: Fall 2010

2. 2 Topics Review of OSPF Areas LSAs show ip ospf database (summary of link state database) show ip route Stub Areas Totally Stubby Areas E1 and E2 routes Default Routes Route Summarization NSSA (Not So Stubby Areas) Multiple ABR Scenario Multiple ASBR Scenario

3. Single Area OSPF - Review

4. 4 Introduction to OSPF OSPF is:  Classless  Link-state routing protocol  Uses the concept of areas for scalability RFC 2328 defines the OSPF metric as an arbitrary value called cost. Cisco IOS software uses bandwidth to calculate the OSPF cost metric.

5. 5 The network Command The area area-id refers to the OSPF area.  A group of OSPF routers that share link-state information.  All OSPF routers in the same area must have the same link-state information in their link-state databases.  This is accomplished by routers flooding their individual link states to all other routers in the area. Router(config-router)# network network-address wildcard-mask area area-id

6. 6 1 – Flooding of link-state information 2 – Building a Topological Database 3 – SPF Algorithm 4 – SPF Tree 5 – Routing Table Link State Concepts

7. 7 Before two routers can form an OSPF neighbor adjacency, they must agree on three values:  Hello interval  Dead interval  Both the interfaces must be part of the same network, including having the same subnet mask.  IP MTU must match Neighbors and Adjacencies

8. 8 Hello Intervals By default, OSPF Hello packets are sent:  10 seconds on multiaccess and point-to-point segments  30 seconds on nonbroadcast multiaccess (NBMA) segments (Frame Relay, X.25, ATM). In most cases, use multicast address ALLSPFRouters at 224.0.0.5.

9. 9 Dead Intervals Cisco uses a default of four times the Hello interval.  40 seconds - Multiaccess and point-to-point segments.  120 seconds - NBMA networks. Dead interval expires  OSPF removes that neighbor from its link-state database.  Floods the link-state information about the “down” neighbor out all OSPF-enabled interfaces.

10. 10 Modifying OSPF Intervals Dead time is counting down from 40 seconds. Refreshed every 10 seconds when R1 receives a Hello from the neighbor. R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.3.3.3 0 FULL/ - 00:00:35 192.168.10.6 Serial0/0/1 10.2.2.2 0 FULL/ - 00:00:36 192.168.10.2 Serial0/0/0

11. 11 Modifying OSPF Intervals Router(config-if)# ip ospf hello-interval seconds Router(config-if)# ip ospf dead-interval seconds

12. Basic OSPF Configuration Lab Topology The router ospf command The network command OSPF Router ID Verifying OSPF Examining the Routing Table

13. 13 OSPF Router ID is an IP address used to uniquely identify an OSPF router.  Also used in the DR and BDR process. 1. Use the IP address configured with the OSPF router-id command. 2. Highest IP address of any of its loopback interfaces. 3. Highest active IP address of any of its physical interfaces. OSPF Router ID Router ID?

14. 14 Verifying New Router IDs (Loopbacks) R1# show ip protocols Routing Protocol is “ospf 1” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 10.1.1.1 R2# show ip protocols Routing Protocol is “ospf 1” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 10.2.2.2 R3# show ip protocols Routing Protocol is “ospf 1” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 10.3.3.3

15. 15 Verifying OSPF Neighbor ID: The router ID of the neighboring router. Pri: The OSPF priority of the interface. State: The OSPF state of the interface. Dead Time: Address: The IP address of the neighbor’s interface Interface: Local interface R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.3.3.3 1 FULL/ - 00:00:30 192.168.10.6 Serial0/0/1 10.2.2.2 1 FULL/ - 00:00:33 192.168.10.2 Serial0/0/0

16. 16 R1# show ip ospf interface serial 0/0/0 Serial0/0/0 is up, line protocol is up Internet Address 192.168.10.1/30, Area 0 Process ID 1, Router ID 10.1.1.1, 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 Verifying OSPF

17. 17 Verifying OSPF R1# show ip protocols Routing Protocol is “ospf 1” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 10.1.1.1 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 172.16.1.16 0.0.0.15 area 0 192.168.10.0 0.0.0.3 area 0 192.168.10.4 0.0.0.3 area 0 Reference bandwidth unit is 100 mbps Routing Information Sources: Gateway Distance Last Update 10.2.2.2 110 11:29:29 10.3.3.3 110 11:29:29 Distance: (default is 110) OSPF Process ID OSPF Router ID Networks OSPF is advertising that are originating from this router OSPF Neighbors Administrative Distance

18. 18 Verifying OSPF R1# show ip ospf Routing Process “ospf 1” with ID 10.1.1.1 Start time: 00:00:19.540, Time elapsed: 11:31:15.776 Supports only single TOS(TOS0) routes Supports opaque LSA Supports Link-local Signaling (LLS) Supports area transit capability Router is not originating router-LSAs with maximum metric Initial SPF schedule delay 5000 msecs Minimum hold time between two consecutive SPFs 10000 msecs Maximum wait time between two consecutive SPFs 10000 msecs Incremental-SPF disabled Minimum LSA interval 5 secs Minimum LSA arrival 1000 msecs Area BACKBONE(0) Number of interfaces in this area is 3 Area has no authentication SPF algorithm last executed 11:30:31.628 ago SPF algorithm executed 5 times

19. 19 Verifying OSPF Any time a router receives new information about the topology (addition, deletion, or modification of a link), the router must:  Rerun the SPF algorithm  Create a new SPF tree  Update the routing table The SPF algorithm is CPU intensive, and the time it takes for calculation depends on the size of the area. R1# show ip ospf Initial SPF schedule delay 5000 msecs Minimum hold time between two consecutive SPFs 10000 msecs Maximum wait time between two consecutive SPFs 10000 msecs

20. 20 Verifying OSPF A flapping link can cause OSPF routers in an area to constantly recalculate the SPF algorithm, preventing proper convergence.  If there is a route in the routing table the router will continue to forward the packet. SPF schedule delay.  To minimize this problem, the router waits 5 seconds (5000 msec) after receiving an LSU before running the SPF algorithm. Minimum hold time:  To prevent a router from constantly running the SPF algorithm, there is an additional hold time of 10 seconds (10,000 ms).  The router waits 10 seconds after running the SPF algorithm before rerunning the algorithm. R1# show ip ospf Initial SPF schedule delay 5000 msecs Minimum hold time between two consecutive SPFs 10000 msecs

21. 21 Verifying OSPF R1# show ip ospf interface serial 0/0/0 Serial0/0/0 is up, line protocol is up Internet Address 192.168.10.1/30, Area 0 Process ID 1, Router ID 10.1.1.1, 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

22. 22 Examining the Routing Table Unlike RIPv2 and EIGRP, OSPF does not automatically summarize at major network boundaries. R1# show ip route Codes: D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 192.168.10.0/30 is subnetted, 3 subnets C 192.168.10.0 is directly connected, Serial0/0/0 C 192.168.10.4 is directly connected, Serial0/0/1 O 192.168.10.8 [110/128] via 192.168.10.2, 14:27:57, Serial0/0/0 172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks O 172.16.1.32/29 [110/65] via 192.168.10.6, 14:27:57, Serial0/0/1 C 172.16.1.16/28 is directly connected, FastEthernet0/0 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks O 10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0 C 10.1.1.1/32 is directly connected, Loopback0

23. The OSPF Metric OSPF Metric Modifying the Cost of the Link

24. 24 OSPF Metric The OSPF metric is called cost. The following passage is from RFC 2328:  A cost is associated with the output side of each router interface. This cost is configurable by the system administrator. The lower the cost, the more likely the interface is to be used to forward data traffic. RFC 2328 does not specify which values should be used to determine the cost.

25. 25 OSPF Metric Cisco IOS software uses the cumulative bandwidths of the outgoing interfaces from the router to the destination network as the cost value. 10 8 is known as the reference bandwidth Cisco IOS Cost for OSPF = 10 8 /bandwidth in bps

26. 26 Reference Bandwidth When this command is necessary, it is recommended that it is used on all routers so the OSPF routing metric remains consistent. R1(config-router)# auto-cost reference-bandwidth ? 1-4294967 The reference bandwidth in terms of Mbits per second. R1(config-router)# auto-cost reference-bandwidth 10000 To increase it to 10GigE (10 Gbps Ethernet) speeds, you need to change the reference bandwidth to 10,000.

27. 27 T1 cost 64 + Fast Ethernet cost 1 = 65 The “Cost = 64” refers to the default cost of the serial interface, 10 8 /1,544,000 bps = 64, and not to the actual 64-Kbps “speed” of the link. R1# show ip route O 10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0 OSPF Accumulates Cost Serial interfaces bandwidth value defaults to T1 or 1544 Kbps.

28. 28 Default Bandwidth on Serial Interfaces On Cisco routers, the bandwidth value on many serial interfaces defaults to T1 (1.544 Mbps). R1# show interface serial 0/0/0 Serial0/0/0 is up, line protocol is up Hardware is GT96K Serial Description: Link to R2 Internet address is 192.168.10.1/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255

29. 29 Modifying the Cost of the Link The bandwidth command is used to modify the bandwidth value used by the Cisco IOS software in calculating the OSPF cost metric.  Same as with EIGRP Router(config-if)# bandwidth bandwidth-kbps R1(config)# inter serial 0/0/0 R1(config-if)# bandwidth 64 R1(config-if)# inter serial 0/0/1 R1(config-if)# bandwidth 256 R1(config-if)# end R1# show ip ospf interface serial 0/0/0 Serial0/0 is up, line protocol is up Internet Address 192.168.10.1/30, Area 0 Process ID 1, Router ID 10.1.1.1, Network Type POINT_TO_POINT, Cost: 1562 Transmit Delay is 1 sec, State POINT_TO_POINT, 100,000,000/64,000 = 1562

30. 30 The ip ospf cost Command An alternative method to using the bandwidth command is to use the ip ospf cost command, which allows you to directly specify the cost of an interface. This will not change the output of the show ip ospf interface command, R1(config)# interface serial 0/0/0 R1(config-if)# ip ospf cost 1562 R1(config)# inter serial 0/0/0 R1(config-if)# bandwidth 64 R1(config-if)# end R1# show ip ospf interface serial 0/0/0 Serial0/0 is up, line protocol is up Internet Address 192.168.10.1/30, Area 0 Process ID 1, Router ID 10.1.1.1, Network Type POINT_TO_POINT, Cost: 1562 100,000,000/64,000 = 1562

31. OSPF and Multiaccess Networks Challenges in Multiaccess Networks DR/BDR Election Process OSPF Interface Priority

32. 32 Solution: Designated Router OSPF elects a Designated Router (DR) to be the collection and distribution point for LSAs sent and received. A Backup Designated Router (BDR) is also elected in case the DR fails. All other routers become DROthers.

33. 33 DROthers only form full adjacencies with the DR and BDR in the network.  send their LSAs to the DR and BDR  using the multicast address 224.0.0.6 (ALLDRouters, all DR routers). R1 sends LSAs to the DR.  The BDR listens, too. The DR is responsible for forwarding the LSAs from R1 to all other routers.  DR uses the multicast address 224.0.0.5 (AllSPFRouters, all OSPF routers).  Only one router doing all the flooding. DROther 224.0.0.6 224.0.0.5

34. 34 DR/BDR Election The following criteria are applied: 1. DR: Router with the highest OSPF interface priority. 2. BDR: Router with the second highest OSPF interface priority. 3. If OSPF interface priorities are equal, the highest router ID is used to break the tie. Default OSPF interface priority is 1. Current configuration, the OSPF router ID is used to elect the DR and BDR. DR BDR DROther

35. 35 RouterA# show ip ospf interface fastethernet 0/0 FastEthernet0/0 is up, line protocol is up Internet Address 192.168.1.1/24, Area 0 Process ID 1, Router ID 192.168.31.11, Network Type BROADCAST, Cost: 1 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) 192.168.31.33, Interface address 192.168.1.3 Backup Designated router (ID) 192.168.31.22, Interface address 192.168.1.2 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Verifying Router States

36. 36 Timing of DR/BDR Election If I booted first and started the election before the others were ready, I would be the DR!

37. 37 Timing of DR/BDR Election When the DR is elected, it remains the DR until one of the following conditions occurs:  The DR fails.  The OSPF process on the DR fails.  The multiaccess interface on the DR fails. If the DR fails, the BDR assumes the role of DR, and an election is held to choose a new BDR. DR failed! I am now the DR! Elections will now happened for BDR I am now the BDR! DR BDR

38. 38 If a new router enters the network after the DR and BDR have been elected, it will not become the DR or the BDR even if it has a higher OSPF interface priority or router ID than the current DR or BDR. DR BDR Timing of DR/BDR Election DROther I am a new router with the highest Router ID. I cannot force a new DR or BDR election, so I am a DROther.

39. 39 A previous DR does not regain DR status if it returns to the network. DR BDR Timing of DR/BDR Election DROther I’m back but I don’t get to become DR again. I am now just a DROther. DROther

40. 40 If the BDR fails, an election is held among the DROthers to see which router will be the new BDR. DR BDR Timing of DR/BDR Election BDR Amongst the DROthers I have the highest Router ID, so I am the new BDR! DROther

41. 41 RouterB fails. Because RouterD is the current BDR, it is promoted to DR. RouterC becomes the BDR. DR BDR Timing of DR/BDR Election BDR I am now the new DR! DROther I am now the new BDR!

42. 42 Timing of DR/BDR Election We can change the OSPF interface priority to better control our DR/BDR elections. How can we make sure RouterB is the DR and RouterA is the BDR, regarless of RouterID values? Want to be DR Want to be BDR Highest Router ID To simplify our discussion, we removed RouterD from the topology.

43. 43 OSPF Interface Priority Control the election of these routers with the ip ospf priority interface command. Priority (Highest priority wins):  0 = Cannot become DR or BDR  1 = Default  Therefore, the router ID determines the DR and BDR. Priorities are an interface-specific value, they provide better control of the OSPF multiaccess networks. They also allow a router to be the DR in one network and a DROther in another. Router(config-if)# ip ospf priority {0 - 255}

44. 44 OSPF Interface Priority The OSPF interface priority can be viewed using the show ip ospf interface command. RouterA# show ip ospf interface fastethernet 0/0 FastEthernet0/0 is up, line protocol is up Internet Address 192.168.1.1/24, Area 0 Process ID 1, Router ID 192.168.31.11, Network Type BROADCAST, Cost: 1 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) 192.168.31.33, Interface address 192.168.1.3 Backup Designated router (ID) 192.168.31.22, Interface address 192.168.1.2 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

45. 45 After doing a shutdown and a no shutdown on the Fast Ethernet 0/0 interfaces of all three routers, we see the result of the change of OSPF interface priorities. RouterA(config)# interface fastethernet 0/0 RouterA(config-if)# ip ospf priority 200 RouterB(config)# interface fastethernet 0/0 RouterB(config-if)# ip ospf priority 100 Pri = 200 Pri = 100 Highest priority wins

46. 46 Clarifications regarding DR/BDR Hello packets are still exchanged between all routers on a multi- access segment (DR, BDR, DROthers,….) to maintain neighbor adjacencies. OSPF LSA packets (coming) are packets which are sent from the BDR/DROthers to the DR, and then from the DR to the BDR/DROthers. (The reason for a DR/BDR.) Normal routing of IP packets still takes the lowest cost route, which might be between two DROthers.

47. More OSPF Configuration Redistributing an OSPF Default Route Fine-tuning OSPF

48. 48 Redistributing an OSPF Default Route If the default-information originate command is not used, the default “quad zero” route will not be propagated to other routers in the OSPF area. R1(config)# interface loopback 1 R1(config-if)# ip add 172.30.1.1 255.255.255.252 R1(config-if)# exit R1(config)# ip route 0.0.0.0 0.0.0.0 loopback 1 R1(config)# router ospf 1 R1(config-router)# default-information originate The static default route is using the loopback as an exit interface because the ISP router in this topology does not physically exist.

49. 49 R3’s Routing Table R3# show ip route Gateway of last resort is 192.168.10.5 to network 0.0.0.0 192.168.10.0/30 is subnetted, 3 subnets O 192.168.10.0 [110/1952] via 192.168.10.5, 00:00:38, S0/0/0 C 192.168.10.4 is directly connected, Serial0/0/0 C 192.168.10.8 is directly connected, Serial0/0/1 172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks C 172.16.1.32/29 is directly connected, FastEthernet0/0 O 172.16.1.16/28 [110/391] via 192.168.10.5, 00:00:38, S0/0/0 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 10.3.3.3/32 is directly connected, Loopback0 O 10.10.10.0/24 [110/782] via 192.168.10.9, 00:00:38, S0/0/1 O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0

50. 50 External Type 2 Route E2 denotes that this route is an OSPF External Type 2 route. OSPF external routes fall in one of two categories:  External Type 1 (E1)  External Type 2 (E2) OSPF accumulates cost for an E1 route as the route is being propagated throughout the OSPF area.  This process is identical to cost calculations for normal OSPF internal routes. E2 route is always the external cost, irrespective of the interior cost to reach that route.  In this topology, because the default route has an external cost of 1 on the R1 router, R2 and R3 also show a cost of 1 for the default E2 route.  E2 routes at a cost of 1 are the default OSPF configuration.  More later R3# show ip route O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0

51. Steps to OSPF Operation with States 1. Establishing router adjacencies (Routers are adjacent)  Down State – No Hello received  Init State – Hello received, but not with this router’s Router ID  “Hi, my name is Carlos.” “Hi, my name is Maria.”  Two-way State – Hello received, and with this router’s Router ID  “Hi, Maria, my name is Carlos.” “Hi, Carlos, my name is Maria.” 2. Electing DR and BDR – Multi-access (broadcast) segments only  ExStart State with DR and BDR  Two-way State with all other routers 3. Discovering Routes  ExStart State  Exchange State  Loading State  Full State (Routers are “fully adjacent”) 4. Calculating the Routing Table 5. Maintaining the LSDB and Routing Table

52. 52 Hello 10.6.0.1 Hello 10.5.0.1 Hello 10.6.0.1 10.5.0.1 Hello 10.5.0.1 10.6.0.1 DownInitDownInit 2-way Down State - Init State – Two Way State Down State - OSPF routers send Hello packets at regular intervals (10 sec.) to establish neighbors. When a router (sends or) receives its first Hello packet, it enters the init state.  Hello packet contains a list of known neighbors. When the router sends a Hello packet (unicast reply) to the neighbor with its RouterID and the neighbor sends a Hello packet packet back with that Router ID, the router’s interface will transition to the two-way state. Now, the router is ready to take the relationship to the next level. 1. Establishing Adjacencies

53. 53 Steps to OSPF Operation with States (cont) Explanations in Notes Section

54. Couple of notes on link state flooding… OSPF is a link state routing protocol and does not send periodic updates like RIP. OSPF only floods link state state advertisements when there is a change in topology (this includes when a routers are first booted). OSPF uses hop-by-hop flooding of LSAs; an LSA received on one interface are flooded out other OSPF enabled interfaces. If a link state entry in the LSDB (Link State DataBase) reaches an age of 60 minutes (MaxAge) without being updated, it is removed and SPF is recalculated. Every 30 minutes (LSRefreshTime), OSPF routers flood only their link states to all other routers (in the area).  This is known as a “paranoid update”  These do not trigger SPF recalculations. Special note: When a link goes down and a router wants to send a LSA to tell other routers to remove this link state, it sends this link state with a value of 60 minutes (MAXAGE).

55. Single Area OSPF End of Review CIS 185 Advanced Routing Rick Graziani Cabrillo College graziani@cabrillo.edu

56. 56 Issues with large OSPF nets Large link-state table  Each router maintains a LSDB for all links in the area  The LSDB requires the use of memory Frequent SPF calculations  A topology change in an area causes each router to re-run SPF to rebuild the SPF tree and the routing table.  A flapping link will affect an entire area.  SPF re-calculations are done only for changes within that area. Large routing table  Typically, the larger the area the larger the routing table.  A larger routing table requires more memory and takes more time to perform the route look-ups. Solution: Divide the network into multiple areas

57. 57 OSPF uses “Areas” Hierarchical routing enables you to separate large internetworks (autonomous systems) into smaller internetworks that are called areas. With this technique, routing still occurs between the areas (called inter-area routing). Some operations are restricted within an area:  Flooding of LSAs  Recalculating the database  Re-running the SPF algorithm

58. 58 OSPF Router Types

59. 59 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.

60. 60 Question: I understand the routing table is recalculated every time the router receives an new version of an LSA. Does OSPF recalculate its routing table when their is a topology change in another area? show ip ospf displays no change in SPF execution, but show ip ospf database shows a change in the topology? Answer: Good question! OSPF areas are designed to keep issues like flapping links within an area.  SPF is not recalculated if the topology change is in another area.  The interesting thing is that OSPF distributes inter-area (between areas) topology information using a distance-vector method.  OSPF uses link-state principles only within an area.  ABRs do not announce topological information between areas, instead, only routing information is injected into other areas.  ABRs relay routing information between areas via distance vector technique similar to RIP or EIGRP.  This is why show ip ospf does not show a change in the number of times SPF has been executed when the topology change is in another area. Note: It is still a good idea to perform route summarization between areas, announcing multiple routes as a single inter-area route. This will hide any changes in one area from affecting routing tables in other areas. An advantage of Multiple Areas

61. 61 OSPF Packet Types In CCNA we discussed various OSPF packets OSPF packet types

62. 62 OSPF Type 4 - Link State Advertisements In CCNP we will look at OSPF Type 4 packets more closely OSPF packet types

63. 63 OSPF packet types OSPF Type-4 packets have 7 LSA packets (later)

64. 64 LSAs used for discovering routes and reaching Full State, along with Maintain Routes LSA Types

65. 65 LSA Types LSA Types 1 through 5 We will look at these in detail as we discuss areas in this chapter. LSA Type 6 MOSPF (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. LSA Type 7 NSSA External Link Entry Next presentation! LSA Type 8 External attributes LSA for BGP Not supported by Cisco N/A LSA Type 9, 10, or 11 Opaque LSAs Future upgrades

66. 66 Area Types Standard or Normal Areas  Backbone  Non-Backbone Stub Areas  Stub Area  Totally Stubby Area  Not-so-stubby-area (NSSA)

67. 67 Area Types

68. 68 Part I - LSAs using all normal areas Multi Area OSPF Normal Areas ASBR ABR Internal Backbone Area What are the router types?

69. 69 Routes Received on all OSPF Routers Overview of Normal Areas – This will all be explained! Receives all routes from within A.S.: Within the local area – LSA 1 and LSA 2 From other areas (Inter-Area) – LSA 3, LSA 4, LSA 5 Receives all routes from External A.S.’s (External AS means routes not from this OSPF routing domain): From external AS’s – LSA 5 As long as routes are being redistributed by the ASBR (more later) Default Route Received only if default-information-originate command was used (later) If default-information-originate command is not used, then the default route is not received Part I - LSAs using all normal areas

70. 70 1. OSPF Multi-Areas - All Normal Areas R33 router ospf 1 network 172.16.1.0 0.0.0.255 area 1 network 172.30.1.0 0.0.0.255 area 1 R22 router ospf 1 network 172.16.1.0 0.0.0.255 area 1 network 172.30.2.0 0.0.0.255 area 1 R1 router ospf 1 network 10.0.0.0 0.0.0.3 area 0 network 9.0.0.0 0.0.0.3 area 0 network 172.16.1.0 0.0.0.255 area 1 network 172.16.2.0 0.0.0.255 area 1 R2 router ospf 1 network 192.168.2.0 0.0.0.255 area 0 network 10.0.0.0 0.0.0.3 area 0 network 11.0.0.0 0.0.0.3 area 0 default-information originate ip route 0.0.0.0 0.0.0.0 serial 0/2 R3 router ospf 1 network 11.0.0.0 0.0.0.3 area 0 network 9.0.0.0 0.0.0.3 area 0 network 172.16.10.0 0.0.0.255 area 51 network 172.16.11.0 0.0.0.255 area 51 network 99.0.0.0 0.0.0.3 area 51 R100 router ospf 1 network 99.0.0.0 0.0.0.3 area 51 network 99.1.0.0 0.0.255.255 area 51 network 99.0.0.4 0.0.0.3 area 51 R200 router ospf 1 network 99.0.0.4 0.0.0.3 area 51 network 99.0.0.0 0.0.255.255 area 51 ABR contains network statements for each area it belongs to, using the proper area value.

71. 71 Part I - LSAs using all normal areas Multi Area OSPF Normal Areas ASBR ABR Internal Backbone Area What are the router types?

72. 72 Part I - LSAs using all normal areas Multi Area OSPF Normal Areas ASBR ABR Internal Backbone Area What are the router types?

73. 73 Part I - LSAs using all normal areas Multi Area OSPF Normal Areas ASBR ABR Internal Backbone Area What are the router types?

74. 74 Understanding LSAs (FYI ONLY) show ip ospf database  This is not the link state database, only a summary.  It is a tool to help determine what routes are included in the routing table.  We will look at this output to learn the tool as well as become familiar with the different types of LSAs.  To view the link state database use: show ip ospf database [router|network|…] 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | LS type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LSA Header

75. 75 LSA 1 – Router LSA Generated by each router for each area it belongs to. Describes the states of the links in the area to which this router belongs. Flooded only within the area. On multi-access networks, sent to the DR. Denoted by just an “O” in the routing table or “C” if the network is directly connected. ABR will include a set of LSA 1’s for each area it belongs to. When a new LSA 1 is received and installed in the LSDB, the router forwards that LSA, using hop-by-hop or asynchronous flooding. Router A’s LSA 1s which are flooded to all other routers in this area. “Leaf” network LSA 1 - Router Link States

76. 76 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 |V|E|B| 0 | # links | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | # TOS | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TOS | 0 | TOS metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | LSA 1 - Router Link States

77. 77 LSA 1 – Router Link States LSA 1’s Each router floods their LSA 1s ONLY within their own area. LSA 1s only announce the links (networks) within the area. Router receives LSA 1s from neighbor, floods those LSA 1s to other neighbors within the same area.

78. 78 LSA 1 - Router Link States For Router Links: Link State ID: Advertising Router ID Advertising Router: Router ID of the router that created this LSA 1 Bottom line: Router Link States (LSA1’s) should display all the RouterIDs of routers in that area, including its own. Rick’s reminder: LSA 1 -> “my one area” R100# show ip ospf database OSPF Router with ID (100.100.100.100) (Process ID 1) Router Link States (Area 51) <- Note the Area ( LSA 1 - Links in this area.) Link ID ADV Router Age Seq# Checksum LinkCnt 3.3.3.3 3.3.3.3 42 0x80000004 0x00168d 4 100.100.100.100 100.100.100.100 10 0x80000005 0x00472f 4 200.200.200.200 200.200.200.200 10 0x80000002 0x00db5f 1

79. 79 R100# show ip route 172.16.0.0/24 is subnetted, 4 subnets O 172.16.10.0 [110/65] via 99.0.0.1, 00:08:30, Serial0/0 O 172.16.11.0 [110/65] via 99.0.0.1, 00:08:30, Serial0/0 LSA 1 - Router Link States Denoted by just an “O” in the routing table, or a “C” Note: Only partial routing tables will be shown

80. 80 LSA 1’s LSA 1 - Router Link States

81. 81 LSA 2 – Network LSA Generated by the DR on every multi-access network Denoted by just an “O” in the routing table or “C” if the network is directly connected. Flooded only within the originating area. LSA 2’s are in link state database for all routers within area, even those routers on not on multi-access networks or DRs on other multi- access networks in the same area. ABR may include a set of LSA 2s for each area it belongs to. LSA 2 - Network Link States

82. 82 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attached Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | LSA 2 - Network Link States

83. 83 LSA 2s LSA 2s flooded within area by DR. LSA 2’s

84. 84 R3# show ip ospf database Net Link States (Area 51) Link ID ADV Router Age Seq# Checksum 99.0.0.6 200.200.200.200 241 0x80000002 0x006159 LSA 2 - Network Link States Link ID IP address of DR on MultiAccess Network ADV Router Router ID of DR Bottom line: Net Link States (LSA2’s) should display the RouterIDs of the DRs on all multi-access networks in the area and their IP addresses. Rick’s reminder: LSA 2 -> “Ethernet = Layer 2 or D R” 1 2

85. 85 LSA 2’s LSA 2 - Network Link States

86. 86 LSA 3 – Summary LSA Originated by the ABR. Describes links between ABR and Internal Routers of the Local Area ABR will include a set of LSA 3’s for each area it belongs to. LSA 3s are flooded throughout the backbone (Area 0) and to other ABRs. Routes learned via LSA type 3s are denoted by an “IA” (Inter-area) in the routing table. LSA 3 – Summary Net Link States

87. 87 LSA 3 – Summary LSAs LSA 3 – Summary LSA Originated by the ABR. Describes links between ABR and Internal Routers of the Local Area ABR will include a set of LSA 3’s for each area it belongs to. LSA 3s are flooded throughout the backbone (Area 0) and to other ABRs. Routes learned via LSA type 3s are denoted by an “IA” (Inter-area) in the routing table. LSA 3’s LSA 1’s LSA 3’s ABR

88. 88 LSA 3 – Summary LSAs LSA 1’s LSA 3’s ABR

89. 89 LSA 3 – Summary LSAs LSA 3’s LSA 1’s

90. 90 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 3 or 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TOS | TOS metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | LSA 3 – Summary Net Link States

91. 91 Routers only see the topology of the area they belong to. When a link in one area changes, the adjacent routers originate in LSA 1’s and flood them within the area, causing intra-area (internal) routers to re-run the SPF and recalculating the routing table. ABRs do not announce topological information between areas. ABRs only inject routing information into other areas, which is basically a distance-vector technique. LSA 3’s LSA 1’s LSA 3’s Process using DV technique not LSA 1 Link States. New or change, do not run SPF algorithm. LSA 3 – Summary Net Link States X

92. 92 ABRs calculate intra-area routes and announce them to all other areas as inter-area routes, using LSA 3’s. OSPF ABRs will only announce inter-area routes that were learned from the backbone area, area 0. The backbone area serves as a repository for inter-area routes. This keeps OSPF safe from routing loops. LSA 3’s LSA 1’s LSA 3’s LSA 3 – Summary Net Link States

93. 93 LSA 3 LSA 1’s Not ABR In normal operation, OSPF ABRs will only announce inter-area routes that were learned from the backbone area, area 0. RTC does not forward LSA 3’s from Area 1 to Area 51, and does not forward LSA 3’s from Area 51 to Area 1. The backbone area serves as a repository for inter-area routes. This keeps OSPF safe from routing loops.

94. 94 LSA 3 Normal Areas LSA 1’s Not ABR RTC does not forward the LSA 3’s back into Area 1, or routing loops may develop. Note: RTC will create LSA 1’s and flood them within the appropriate area. OSPF specification states that ABRs are restricted to considering LSA 3’s only from the backbone area to avoid routing information loops.

95. 95 Normal Areas LSA 1’s LSA 3 X Area 1 routers re-run SPF, creates new SPF tree and updates routing table. Update is sent to Area 0 and Area 51 routers using a “distance vector update technique.” SPF not re-run, but routers update routing table. Topology Change: Down Link When a router detects a topology change it immediately sends out LSA 1’s (Router LSAs) with the change. Age of the LSA is set to MaxAge (3,600 seconds) – Routers remove this entry from their LSDB (Link State Data Base). Routers that receive the LSA 1’s, within the area of the change: Re-run their SPF algorithm Build a new SPF tree Update IP routing tables. (Continued next slide)

96. 96 Normal Areas LSA 1’s LSA 3 X Area 1 routers re-run SPF, creates new SPF tree and updates routing table. Update is sent to Area 0 and Area 51 routers using a “distance vector update technique.” SPF not re-run, but routers update routing table. Topology Change: Down Link ABR RTA receives the LSA 1 and recalculate their SPF for that area, Area 1. RTA floods the change as a LSA 3 within its other area, Area 0. RTB receives the LSA 3 and floods it within Area 51. Area 0 and Area 51 routers do not recalculate their SPFs, but inject the change into their routing tables.

97. 97 R33# show ip ospf database Summary Net Link States (Area 1) Link ID ADV Router Age Seq# Checksum 10.0.0.0 1.1.1.1 130 0x8000000c 0x00ec09 9.0.0.0 1.1.1.1 130 0x8000000d 0x00ec09 192.168.2.0 1.1.1.1 130 0x8000000e 0x00ec09 11.0.0.0 1.1.1.1 130 0x8000000f 0x00ec09 172.16.10.0 1.1.1.1 130 0x80000010 0x00ec09 172.16.11.0 1.1.1.1 130 0x80000011 0x00ec09 99.0.0.0 1.1.1.1 130 0x80000012 0x00ec09 99.0.0.4 1.1.1.1 130 0x80000013 0x00ec09 99.1.0.0 1.1.1.1 130 0x80000014 0x00ec09 LSA 3 – Summary Net Link States (INTERNAL) Link ID = IP network addresses of networks in other areas ADV Router = ABR Router ID sending the LSA-3 Bottom line: Should see networks in other areas and the ABR advertising that route. Rick’s reminder: LSA 3 -> “networks sent by the A B R” 1 2 3 ABR

98. 98 R1# show ip ospf database Summary Net Link States (Area 1) <- Per Area Link ID ADV Router Age Seq# Checksum 10.0.0.0 1.1.1.1 255 0x8000000c 0x00ec09 9.0.0.0 1.1.1.1 255 0x8000000d 0x00ec09 192.168.2.0 1.1.1.1 255 0x8000000e 0x00ec09 11.0.0.0 1.1.1.1 255 0x8000000f 0x00ec09 172.16.10.0 1.1.1.1 255 0x80000010 0x00ec09 172.16.11.0 1.1.1.1 255 0x80000011 0x00ec09 99.0.0.0 1.1.1.1 255 0x80000012 0x00ec09 99.0.0.4 1.1.1.1 255 0x80000013 0x00ec09 99.1.0.0 1.1.1.1 255 0x80000014 0x00ec09 LSA 3 – Summary Net Link States (ABR) ABR will show all routes it is injecting into the other area including: LSA 3s from other areas LSA 1s from it’s adjacent area it is injecting into this area Bottom line: Should see networks in other areas and the ABR advertising that route. Rick’s reminder: LSA 3 -> “networks sent by the A B R” 1 2 3

99. 99 R2# show ip route 99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks O IA 99.0.0.0/30 [110/1626] via 11.0.0.2, 00:43:01, Serial0/1 O IA 99.0.0.4/30 [110/1627] via 11.0.0.2, 00:43:01, Serial0/1 O IA 99.1.0.0/16 [110/1627] via 11.0.0.2, 00:43:01, Serial0/1 172.16.0.0/24 is subnetted, 4 subnets O IA 172.16.1.0 [110/65] via 10.0.0.1, 00:42:21, Serial0/0 O IA 172.16.2.0 [110/65] via 10.0.0.1, 00:42:51, Serial0/0 O IA 172.16.10.0 [110/1563] via 11.0.0.2, 00:43:01, Serial0/1 O IA 172.16.11.0 [110/1563] via 11.0.0.2, 00:43:01, Serial0/1 172.30.0.0/24 is subnetted, 2 subnets O IA 172.30.1.0 [110/66] via 10.0.0.1, 00:42:21, Serial0/0 O IA 172.30.2.0 [110/66] via 10.0.0.1, 00:42:21, Serial0/0 LSA 3 – Summary Net Link States Routes learned via LSA type 3s are denoted by an “IA” (Inter-Area Routes) in the routing table.

100. 100 LSA 3’s LSA 1’s LSA 3’s

101. 101 LSA 4 – ASBR Summary LSA Originated by the ABR. Flooded throughout the area. Describes the reachability to the ASBRs  Advertises an ASBR (Router ID) not a network Included in routing table as an “IA” route. Exceptions Not flooded to Stub and Totally Stubby networks. More on this later LSA 4 – ASBR Summary Link States

102. 102 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 3 or 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TOS | TOS metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | LSA 4 – ASBR Summary Link States

103. 103 LSA 4 – ASBR Summary Link States How does the ABRs know about the ASBR? ASBR sends a type 1 Router LSA with a bit (external bit – e bit) that is set to identify itself as the ASBR. LSA 1’s (e bit) LSA 4

104. 104 R1# show ip ospf database Summary ASB Link States (Area 1) Link ID ADV Router Age Seq# Checksum 2.2.2.2 1.1.1.1 1482 0x8000000b 0x00ec09 LSA 4 – ASBR Summary Link States (ABR) Link ID - Router ID of ASBR ADV Router - Router ID ABR advertising route Bottom line: Routers in non-area 0, should see Router ID of ASBR and its ABR to get there. Rick’s reminder: LSA 4 -> “Reachability to the A S B R” 1 2 3 4 ASBR(This) ABR ABR

105. 105 R33# show ip ospf database Summary ASB Link States (Area 1) Link ID ADV Router Age Seq# Checksum 2.2.2.2 1.1.1.1 130 0x8000000b 0x00ec09 LSA 4 – ASBR Summary Link States (INTERNAL) Link ID - Router ID of ASBR ADV Router - Router ID ABR advertising route Bottom line: Routers in non-area 0, should see Router ID of ASBR and its ABR to get there. Rick’s reminder: LSA 4 -> “Reachability to the A S B R” 1 2 3 4 ASBR(Advertising) ABR ABR

106. 106 LSA 1’s e bit LSA 4 LSA 4 – ASBR Summary Link States

107. 107 LSA 5 – AS External LSA Originated by the ASBR. Describes destination networks external to the Autonomous System (This OSPF Routing Domain) Flooded throughout the OSPF AS except to stub and totally stubby areas Denoted in routing table as E1 or E2 (default) route (soon) ASBR – Router which “redistributes” routes into the OSPF domain. Exceptions Not flooded to Stub and Totally Stubby networks. More on this later LSA 5 - AS External Link States

108. 108 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| 0 | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Forwarding address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | External Route Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| TOS | TOS metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Forwarding address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | External Route Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |... | LSA 5 - AS External Link States

109. 109 R2 (ASBR) router ospf 1 redistribute static ip route 57.0.0.0 255.0.0.0 ser 0/3 Added -> ASBR

110. 110 “Redistribute” command creates an ASBR router. LSA 5s  Originated by the ASBR.  Describes destination networks external to the OSPF Routing Domain  Flooded throughout the OSPF AS except to stub and totally stubby areas R2 (ASBR) router ospf 1 redistribute static ip route 57.0.0.0 255.0.0.0 ser 0/3 LSA 5’s LSA 5

111. 111 R1# show ip ospf database Type-5 AS External Link States <- Note, NO Area! Link ID ADV Router Age Seq# Checksum Tag 0.0.0.0 2.2.2.2 2088 0x80000003 0x00ddeb 1 57.0.0.0 2.2.2.2 2089 0x80000003 0x00ddeb 0 Link ID = External Networks ADV Router = Router ID of ASBR Note: For ABRs: There is only one set of “AS External Link States” in database summary. In other words, an ABR router will only show one set of “AS External Link States,” not one per area. Bottom line: All Routers should see External networks and the Router ID of ASBR to get there. Rick’s reminder: LSA 5 -> O T H E R networks 1 2 3 4 5 Note: Packet Tracer does not support LSA 5’s for redistributed routes ASBR R2 (ASBR) router ospf 1 redistribute static default-information originate ip route 0.0.0.0 0.0.0.0 ser 0/2 ip route 57.0.0.0 255.0.0.0 ser 0/3

112. 112 R1# show ip route O E2 57.0.0.0/8 [110/20] via 10.0.0.2, 00:16:02, Serial0/0 O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:16:02, Serial0/0 Designated by “E2” Notice that the cost is 20 for all redistributed routes, we will see why later. It has to do with E2 routes and where the default cost is 20. –Redistribute command (Route Optimization chapter): If a value is not specified for the metric option, and no value is specified using the default- metric command, the default metric value is 0, except for OSPF where the default cost is 20. Cost of 1 for the redistributed route. LSA 5 - AS External Link States

113. 113 R33# show ip ospf database Type-5 AS External Link States <- Note, NO Area! Link ID ADV Router Age Seq# Checksum Tag 0.0.0.0 2.2.2.2 278 0x80000003 0x00ddeb 1 57.0.0.0 2.2.2.2 1187 0x80000003 0x00ddeb 0 LSA 5 - AS External Link States R33# show ip route O E2 57.0.0.0/8 [110/20] via 10.0.0.2, 00:16:02, Serial0/0 O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:16:02, Serial0/0

114. 114 E1 vs. E2 External Routes External routes fall under two categories:  external type 1  external type 2 (default) The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route. A type 1 cost is the addition of the external cost and the internal cost used to reach that route. A type 1 route is always preferred over a type 2 route for the same destination. More later… LSA 5 - AS External Link States

115. Stub Areas

116. 116 Stub Areas Considerations for both Stub and Totally Stubby Areas An area could be qualified a stub when:  There is a single exit point (a single ABR) from that area. More than one ABR can be used, but be ready to “accept non-optimal routing paths.”  If routing to outside of the area does not have to take an optimal path. The area is not needed as a transit area for virtual links (later). The ASBR is not within the stub area The area is not the backbone area (area 0) Stub areas will result in memory and processing savings depending upon the size of the network.

117. 117 Stub Area

118. 118 Receives all routes from within A.S.: Within the local area - LSA 1s and LSA 2s (if appropriate) From other areas (Inter-Area) - LSA 3s Does not receive routes from External A.S. (External Routes). ABR: ABR blocks all LSA 4s and LSA 5s. ‘If LSA 5s are not known inside an area, LSA 4s are not necessary.’ LSA 3s are propagated by the ABR. Note: Default route is automatically injected into stub area by ABR  External Routes: Once the ABR gets a packet headed to a default route, it must have a default route, either static or propagated by the ASBR via default information originate (coming!) Configuration: All routers in the area must be configured as “stub” Stub Areas

119. 119 R3 (ABR) router ospf 1 area 51 stub << Command: area area stub R100 (INTERNAL) router ospf 1 area 51 stub << Command: area area stub R200 (INTERNAL) router ospf 1 area 51 stub << Command: area area stub Stub Areas – Additional Commands All routers in the area must be configured as “stub” including the ABR

120. 120 Stub Area LSA 4 Blocked LSA 5Blocked LSA 5 LSA 3 Default route to ABR injected Sent by ABR: LSA 3s (Inter-Area routes) Blocked: LSA 4s (reachability to ASBR) LSA 5s (External routes) The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own. Changes in External routes no longer affect Stub Area routing tables. We only see routes in our area, other areas, and a default route. No external routes. LSA 1s still sent within each area.

121. 121 R100# show ip ospf database Summary Net Link States (Area 51) Link ID ADV Router Age Seq# Checksum 9.0.0.0 3.3.3.3 1752 0x80000037 0x00ba22 0.0.0.0 3.3.3.3 1612 0x80000038 0x00ca50 11.0.0.0 3.3.3.3 625 0x80000039 0x00db11 192.168.2.0 3.3.3.3 614 0x8000003a 0x00dd10 10.0.0.0 3.3.3.3 614 0x8000003b 0x00dd10 172.16.2.0 3.3.3.3 614 0x8000003c 0x00dd10 172.16.1.0 3.3.3.3 614 0x8000003d 0x00dd10 172.30.2.0 3.3.3.3 614 0x8000003e 0x00dc11 172.30.1.0 3.3.3.3 614 0x8000003f 0x00dc11 No LSA 4s or LSA 5s for stub area routers. Default Route injected by ABR (LSA 3) Stub Areas

122. 122 R200# show ip route 9.0.0.0/30 is subnetted, 1 subnets O IA 9.0.0.0 [110/129] via 99.0.0.5, 00:25:52, FastEthernet0/0 10.0.0.0/30 is subnetted, 1 subnets O IA 10.0.0.0 [110/1691] via 99.0.0.5, 00:25:52, FastEthernet0/0 11.0.0.0/30 is subnetted, 1 subnets O IA 11.0.0.0 [110/1627] via 99.0.0.5, 00:25:52, FastEthernet0/0 99.0.0.0/8 is variably subnetted, 4 subnets, 2 masks O 99.0.0.0/30 [110/65] via 99.0.0.5, 00:25:52, FastEthernet0/0 C 99.0.0.4/30 is directly connected, FastEthernet0/0 O 99.1.0.0/16 [110/2] via 99.0.0.5, 00:25:52, FastEthernet0/0 C 99.2.0.0/16 is directly connected, FastEthernet0/1 172.16.0.0/24 is subnetted, 4 subnets O IA 172.16.1.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0 O IA 172.16.2.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0 O 172.16.10.0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0 O 172.16.11.0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0 172.30.0.0/24 is subnetted, 2 subnets O IA 172.30.1.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0 O IA 172.30.2.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0 O IA 192.168.2.0/24 [110/1628] via 99.0.0.5, 00:25:52, FastEthernet0/0 200.200.200.0/32 is subnetted, 1 subnets C 200.200.200.200 is directly connected, Loopback0 O*IA 0.0.0.0/0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0 Stub Areas LSA 1’s (Within area) LSA 3’s (Other areas) No LSA 4’s (ASBR) No LSA 5’s (External routes) Default Route (Injected by ABR) NOTE on default route: ABR will advertise a default route with a cost of 1 cost of 65 = 1 (Default) +1 (Fa) + 64 (serial link) The default cost can be modified with the ospf command: ABR(config-router)# area area-id default- cost cost

123. 123 R3# show ip route 3.0.0.0/32 is subnetted, 1 subnets C 3.3.3.3 is directly connected, Loopback0 9.0.0.0/30 is subnetted, 1 subnets C 9.0.0.0 is directly connected, Serial0/2 10.0.0.0/30 is subnetted, 1 subnets O 10.0.0.0 [110/1626] via 11.0.0.1, 00:00:41, Serial0/3 11.0.0.0/30 is subnetted, 1 subnets C 11.0.0.0 is directly connected, Serial0/3 99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks C 99.0.0.0/30 is directly connected, Serial0/0 O 99.0.0.4/30 [110/65] via 99.0.0.2, 00:00:46, Serial0/0 O 99.1.0.0/16 [110/65] via 99.0.0.2, 00:00:46, Serial0/0 172.16.0.0/24 is subnetted, 4 subnets O IA 172.16.1.0 [110/1627] via 11.0.0.1, 00:00:31, Serial0/3 O IA 172.16.2.0 [110/1627] via 11.0.0.1, 00:00:31, Serial0/3 C 172.16.10.0 is directly connected, FastEthernet0/0 C 172.16.11.0 is directly connected, FastEthernet0/1 172.30.0.0/24 is subnetted, 1 subnets O IA 172.30.1.0 [110/1628] via 11.0.0.1, 00:00:01, Serial0/3 O 192.168.2.0/24 [110/1563] via 11.0.0.1, 00:00:41, Serial0/3 O*E2 0.0.0.0/0 [110/1] via 11.0.0.1, 00:00:41, Serial0/3 Stub Areas Notice, there is no automatic default route on ABR, as there are with the internal stub routers. This default route came from the ASBR. In other words the ABR will inject the default route into the stub area whether or not it has a default route in its routing table.

124. Totally Stubby Areas

125. 125 Totally Stubby Area

126. 126 Receives routes from within A.S.: Only from within the local area - LSA 1s and LSA 2s (if appropriate) Does not receive routes from other areas (Inter-Area) - LSA 3s Does not receive routes from External A.S. (External Routes) ABR: ABR blocks all LSA 4s and LSA 5s. ABR blocks all LSA 3s, except propagating a default route. Default route is injected into totally stubby area by ABR. Configuring: All routers must be configured as “stub” ABR must be configured as “stub no-summary” Totally Stubby Areas

127. 127 R1: (ABR) router ospf 1 area 1 stub no-summary ^^ Command: area area stub no-summary R22 and R33: (INTERNAL ROUTERS) router ospf 1 area 1 stub ^^ Command: area area stub Totally Stubby Areas

128. 128 Stub Area LSA 4 Blocked LSA 5Blocked LSA 5 LSA 3 Default route to ABR injected Blocked: LSA 3s (Inter-Area routes) LSA 4s (reachability to ASBR) LSA 5s (External routes) The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own. Changes in other areas and external routes no longer affect Stub Area routing tables. We only see routes in our area, other areas, and a default route. No external routes. Totally Stubby Area Blocked Default route to ABR injected We only see routes in our area and a default route. No inter-area or external routes. LSA 1s still sent within each area.

129. 129 R33# show ip route 33.0.0.0/32 is subnetted, 1 subnets C 33.33.33.33 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 2 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 O 172.16.2.0 [110/2] via 172.16.1.1, 00:02:13, FastEthernet0/0 172.30.0.0/24 is subnetted, 2 subnets C 172.30.1.0 is directly connected, FastEthernet0/1 O 172.30.2.0 [110/2] via 172.16.1.3, 00:02:23, FastEthernet0/0 O*IA 0.0.0.0/0 [110/2] via 172.16.1.1, 00:02:13, FastEthernet0/0 Totally Stubby Areas Default route is injected into totally stubby area by ABR for all other networks (inter-area and external routes) Does not receive routes from other areas (Inter-Area) Does not receive routes from External A.S. (External Routes) Note: Packet Tracer does not support Totally Stubby Networks (yet)

130. 130 R1# show ip route 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 9.0.0.0/24 is subnetted, 1 subnets C 9.0.0.0 is directly connected, Serial0/1 10.0.0.0/30 is subnetted, 1 subnets C 10.0.0.0 is directly connected, Serial0/0 11.0.0.0/30 is subnetted, 1 subnets O 11.0.0.0 [110/1626] via 10.0.0.2, 00:05:26, Serial0/0 99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks O IA 99.0.0.0/30 [110/1690] via 10.0.0.2, 00:05:26, Serial0/0 O IA 99.0.0.4/30 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0 O IA 99.1.0.0/16 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0 172.16.0.0/24 is subnetted, 4 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 C 172.16.2.0 is directly connected, FastEthernet0/1 O IA 172.16.10.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0 O IA 172.16.11.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0 172.30.0.0/24 is subnetted, 2 subnets O 172.30.1.0 [110/2] via 172.16.1.2, 00:04:51, FastEthernet0/0 O 172.30.2.0 [110/2] via 172.16.1.3, 00:04:41, FastEthernet0/0 O 192.168.2.0/24 [110/65] via 10.0.0.2, 00:05:26, Serial0/0 O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:05:26, Serial0/0 Totally Stubby Areas Notice, there is no automatic default route on ABR, as there are with the internal stub routers. This default route came from the ASBR. In other words the ABR will inject the default route into the stub area whether or not it has a default route in its routing table.

131. 131 Quick Review

132. 132 LSA 1s – Router LSAs show ip ospf database – Router Link States (LSA 1’s)  Should display all the RouterIDs of routers in that area, including its own. show ip route – “O” routes  Routes within that area LSA 1’s

133. 133 LSA 2s – Network LSAs show ip ospf database – Net Link States (LSA 2’s)  Net Link States (LSA2’s) should display the RouterIDs of the DRs on all multi-access networks in the area and their IP addresses. show ip route – “O” routes  Routes within that area LSA 2’s

134. 134 LSA 3 – Summary LSAs LSA 3’s LSA 1’s show ip ospf database – Summary Net Link States (LSA 3’s)  Link ID = IP network addresses of networks in other areas  ADV Router = ABR Router ID sending the LSA-3 show ip route – “IA” (Inter-Area Routes)  Routes in other areas

135. 135 LSA 4 – ASBR Summary Link States show ip ospf database – Summary Net Link States (LSA 3’s)  Link ID = IP network addresses of networks in other areas  ADV Router = ABR Router ID sending the LSA-3 show ip route – “IA” (Inter-Area Routes)  Routes in other areas LSA 1’s ebit LSA 4

136. 136 “Redistribute” command creates an ASBR router. Originated by the ASBR. Describes destination networks external to the OSPF Routing Domain Flooded throughout the OSPF AS except to stub and totally stubby areas R2 (ASBR) router ospf 1 redistribute static ip route 57.0.0.0 255.0.0.0 ser 0/3 LSA 5’s LSA 5 LSA 5 – External Link States

137. 137 Stub Area LSA 4 Blocked LSA 5Blocked LSA 5 LSA 3 Default route to ABR injected Sent by ABR: LSA 3s (Inter-Area routes) Blocked: LSA 4s (reachability to ASBR) LSA 5s (External routes) The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own. Changes in External routes no longer affect Stub Area routing tables. We only see routes in our area, other areas, and a default route. No external routes. Stub Area LSA 1s still sent within each area.

138. 138 Stub Area LSA 4 Blocked LSA 5Blocked LSA 5 LSA 3 Default route to ABR injected Blocked: LSA 3s (Inter-Area routes) LSA 4s (reachability to ASBR) LSA 5s (External routes) The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own. Changes in other areas and external routes no longer affect Stub Area routing tables. We only see routes in our area, other areas, and a default route. No external routes. Totally Stubby Area Blocked Default route to ABR injected We only see routes in our area and a default route. No inter-area or external routes. Totally Stubby Area LSA 1s still sent within each area.

139. Multi Area OSPF – Part 1 of 2 CIS 185 Advanced Routing Rick Graziani Cabrillo College graziani@cabrillo.edu