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Configuring OSPF – Part 2 of 2

Configuring OSPF – Part 2 of 2. CIS 185 CCNP ROUTE Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: Fall 2010. OSPF Part 2. Review of Areas NSSA (Not-So-Stubby-Areas) Multiple ABRs Virtual Links Route Summarization Default Routes Authentication OSPF over Frame Relay

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Configuring OSPF – Part 2 of 2

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

  2. OSPF Part 2 • Review of Areas • NSSA (Not-So-Stubby-Areas) • Multiple ABRs • Virtual Links • Route Summarization • Default Routes • Authentication • OSPF over Frame Relay • LSDB Overload Protection • Passive Interface

  3. Quick Review

  4. LSA 1s – Router LSAs LSA 1’s LSA 1’s LSA 1’s • 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

  5. LSA 2s – Network LSAs LSA 2’s LSA 2’s • 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

  6. LSA 3 – Summary LSAs LSA 3’s 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

  7. LSA 4 – ASBR Summary Link States LSA 1’s ebit LSA 4 LSA 4 • 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

  8. LSA 5 – External Link States R2 (ASBR) router ospf 1 redistribute static ip route 57.0.0.0 255.0.0.0 ser 0/3 LSA 5 LSA 5’s LSA 5 • “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

  9. Stub Area LSA 1s still sent within each area. Stub Area LSA 3 LSA 3 LSA 4 LSA 4 Blocked LSA 5 LSA 5 Blocked Default route to ABR injected We only see routes in our area, other areas, and a default route. No external routes. • 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.

  10. Totally Stubby Area LSA 1s still sent within each area. Totally Stubby Area Stub Area • Blocked LSA 3 LSA 3 • Blocked LSA 4 LSA 4 Blocked • Blocked LSA 5 LSA 5 Blocked Default route to ABR injected Default route to ABR injected We only see routes in our area and a default route. No inter-area or external routes. We only see routes in our area, other areas, and a default route. No external routes. • 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.

  11. NSSA (Not-So-Stubby-Areas)

  12. NSSA (Not So Stubby Area)

  13. NSSA (Not So Stubby Area) • Relatively new, standards based OSPF enhancement, RFC 1587. • NSSA allows an area to remain a stub area, but carry external routing information (Type 7 LSAs) from its stubby end back towards the OSPF backbone. • ASBR in NSSA injects external routing information into the backbone and the NSSA area, but rejects external routing information coming from the ABR. • The ABR does not inject a default route into the NSSA. • This is true for a NSSA Stub, but a default route is injected for a NSSA Totally Stubby area. • Note: RFC 1587, “A default route must not be injected into the NSSA as a summary (type-3) LSA as in the stub area case.” • What??? • Following scenario is only example of how NSSA works. For the purposes of learning about NSSAs, don’t get hung up on the why’s and what if’s.

  14. Default route via RTG NSSA Stub Area • Area 2 would like to be a stub network. • RTH only supports RIP, so RTG will run RIP and redistribute those routes in OSPF. • What type of OSPF router does this make RTG? • Unfortunately, this makes the area 2 router, RTG, an ASBR. • Why is this a problem? • Stub areas cannot contain an ASBR. • In this example RTH does not need to learn routes from OSPF, a default route to RTG is all it needs. • But all OSPF routers must know about the networks attached to the RIP router, RTH. to route packets to it.

  15. Default route via RTG LSA 7 LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked LSA 7 LSA 7 NSSA Stub Area (cont.) • NSSA allow external routes to be advertised into the OSPF AS while retaining the characteristics of a stub area to the rest of the OSPF AS. • ASBR RTG will originate Type-7 LSAs to advertise the external destinations. • These LSA 7s are flooded through the NSSA but are blocked by the NSSA ABR. • The NSSA ABR translates LSA 7s into LSA 5s and flood other areas.

  16. Default route via RTG LSA 7 LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked LSA 7 LSA 7 Type 7 LSA NSSA External Link Entry • Originated by an ASBR connected to an NSSA. • Flooded throughout NSSAs and translated into LSA Type 5 messages by ABRs. • Routes learned via Type-7 LSAs are denoted by either a default “N1” or an “N2” in the routing table. (Relative to E1 and E2).

  17. NSSA Generic Default route via RTG LSA 7 LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked Configuring NSSA Stub Area Configured for all routers in Area 2: router ospf 1 network 172.16.2.0 0.0.0.255 area 2 area 2 nssa LSA 7 LSA 7

  18. NSSA (Not So Stubby Area) NSSA Stub and NSSA Totally Stubby • There are two flavors in NSSA: • Stub • Totally Stubby • Area 2 routers may or may not receive Inter-area routes from RTA, depending upon NSSA configuration • NSSA areas have take on the same characteristics as stub and totally stubby areas, along with the characteristics of NSSA areas.

  19. NSSA –Stub NSSA stub areas: • NSSAs that block type 4 and 5, but allow type 3. • To make a stub area into an NSSA, use the following command under the OSPF configuration. • This command must be configured on all routers in area 2. router ospf 1 area 2 nssa

  20. NSSA Stub Areas Default route via RTG LSA 3s RTH routes:N1/N2 LSA 4s & LSA 5s X LSA 7 0.0.0.0/0 RTH routes:E1/E2 X LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked LSA 7 LSA 7 • Internal NSSA routers have: • All area 2 routes • External routes from RTH (N1/N2) • Inter-area routes from RTB • Area 0 routers have from area 2: • All area 2 routes • External routes from RTH (E1/E2)

  21. NSSA Stub Areas Default route via RTG LSA 3s RTH routes:N1/N2 LSA 4s & LSA 5s X LSA 7 RTH routes:E1/E2 0.0.0.0/0 X LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked Area 2 routers: router ospf 1 network 172.16.2.0 0.0.0.255 area 2 area 2 nssa LSA 7 LSA 7

  22. NSSA – Totally Stubby NSSA Totally Stubby Area • NSSA totally stub areas: Allow only summary default routes and filters everything else. • To configure an NSSA totally stub area, use the following command under the OSPF configuration on the NSSA ABR: router ospf 1 area 2 nssa no-summary • Configure this command on NSSA ABRs only. • All other routers in area 2 (internal area 2 routers): router ospf 1 area 2 nssa • After defining the NSSA totally stub area, area 2 has the following characteristics (in addition to the above NSSA characteristics): • No type 3 (except default), 4 or 5 LSAs are allowed in area 2. • A default route is injected into the NSSA totally stub area as a type 3 summary LSA by the ABR.

  23. NSSA Totally Stubby Areas Default route via RTG LSA 3s X RTH routes: N1/N2 LSA 4s & LSA 5s X LSA 7 RTH routes:E1/E2 0.0.0.0/0 (LSA 3) LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked RTB (ABR): router ospf 1 network 172.16.1.0 0.0.0.255 area 0 network 172.16.2.0 0.0.0.255 area 2 ... area 2 nssa no-summary Area 2 routers: router ospf 1 network 172.16.2.0 0.0.0.255 area 2 area 2 nssa LSA 7 LSA 7

  24. NSSA Totally Stubby Areas Default route via RTG LSA 3s X RTH routes: N1/N2 LSA 4s & LSA 5s X LSA 7 RTH routes:E1/E2 0.0.0.0/0 (LSA 3) LSA 7 LSA 5 LSA 7 LSA 7 LSA 7s Blocked • Internal NSSA routers have: • All area 2 routes • External routes from RTH (N1/N2) • Default route from RTB • Area 0 routers have from area 2: • All area 2 routes • External routes from RTH (E1/E2) LSA 7 LSA 7

  25. Multiple ABRs

  26. Multiple ABRs – If you want to experiment… • Used with “normal” areas. • Routers choose best path to other areas. • Can be used with Stub and Totally Stubby but inefficient routing may occur due to multiple default routes injected by ABR. OSPF-MultiArea-Advanced.pkt

  27. Multiple ABRs Routing Table ABR1 RTA Distribute List Network X LSA 1’s RTB SPF ABR2 RTC • Intra-area routes, OSPF uses pure Link State logic. • All routers inside the area have an identical copy of the LSDB for that area. LSDB Area 51 Area 0

  28. Multiple ABRs To ABR Routing Table ABR1 RTA Link State Logic Distribute List Network X LSA 3’s RTB Distance Vector Logic SPF ABR2 RTC • Best route to reach each ABR is an intra-area SPF calculation. • Interarea routes (LSA 3s) use Distance Vector logic. • ABR advertises Type 3 Summary LSAs (metric but not topology information). • Total cost to Network X = Cost to ABR + ABR’s cost to Network X. • RTB selects best route to Network X via ABR1 and/or ABR2. LSDB LSA 3’s Area 51 Area 0

  29. Multiple ABRs My cost to network X is 10 ABR1 The best path to Network X is via ABR1 with a total cost of 20. RTA Cost = 20 Network X LSA 3’s RTB Cost = 205 My cost to network X is 200 ABR2 RTC Normal Area • Total cost to Network X = Cost to ABR + ABR’s cost to Network X. • RTB selects best route to Network X via ABR1 and/or ABR2. • With stub and totally stubby areas this may not be the most optimum route! Area 51 Area 0

  30. Multiple ABRs – Stub Networks ABR2 is “closer” a lesser metric, so I will use ABR2 for all routes outside my area even if its not the most optimum path. My cost to network X is 10 ABR1 RTA Cost = 10 Network X LSA 3’s RTB Cost = 5 Default Route My cost to network X is 200 ABR2 RTC Totally Stubby Area • Stub and totally stubby area ABRs inject a default route into the area. • Stub ABRs block LSA 4’s and 5’s (external networks) • Totally Stubby ABRs block LSA 3’s (interarea networks), 4’s and 5’s (external networks) • In both cases internal routers can only determine the best route to an ABR, which may not be the best route to the destination network. Area 51 Area 0

  31. Virtual Links

  32. Virtual Links

  33. Virtual Links • All areas in an OSPF autonomous system must be physically connected to the backbone area (area 0). • This is not always possible, you can use a virtual link to connect to the backbone through a non-backbone area. • Transit area - The area through which you configure the virtual link and must have full routing information. • Must be configured between two ABRs. • The transit area cannot be a stub area.

  34. Virtual Links • A virtual link has the following two requirements: • It must be established between two routers that share a common area and are both ABRs. • One of these two routers must be connected to the backbone. • Doyle, “should be used only as a temporary fix to an unavoidable topology problem.”

  35. Virtual Links • Routers do not have to be directly connected.

  36. The command to configure a virtual link is as follows: area <area-id> virtual-link <remote-router-id> RTA(config)#router ospf 1 RTA(config-router)#network 192.168.0.0 0.0.0.255 area 51 RTA(config-router)#network 192.168.1.0 0.0.0.255 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 0.0.0.255 area 3 RTB(config-router)#network 192.168.2.0 0.0.0.255 area 0 RTB(config-router)#area 3 virtual-link 10.0.0.2

  37. Virtual Links • OSPF allows for linking discontinuous parts of the backbone using a virtual link. • OSPF messages between virtual link routers sent as unicast. router ospf 1 area 1 virtual-link 4.4.4.4 interface loopback 1 ip address 1.1.1.1 255.255.255.0 router ospf 4 area 1 virtual-link 1.1.1.1 interface loopback 1 ip address 4.4.4.4 255.255.255.0 C1 C2

  38. Routers use of the Do Not Age (DNA) bit, so periodic reflooding (every 30 minutes) will not occur over this virtual link. • OSPF Note: Router IDs do not have to be advertised and therefore may not be pingable. C1# show ip ospf virtual-links Virtual Link OSPF_VL0 to router 4.4.4.4 is up Run as demand circuit DoNotAge LSA allowed. Transit area 1, via interface FastEthernet0/1, Cost of using 3 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:02 Adjacency State FULL (Hello suppressed)

  39. "In the area 0 via interface OSPF VL0" – confirming that the neighbor relationship does indeed exist in area 0. C1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 4.4.4.4 0 FULL/ - - 10.24.1.1 OSPF_VL0 2.2.2.2 1 FULL/DR 00:00:35 10.21.1.2 FastEthernet0/1 C1# show ip ospf neighbor detail 4.4.4.4 Neighbor 4.4.4.4, interface address 10.24.1.1 In the area 0 via interface OSPF_VL0

  40. Route Summarization

  41. Route Summarization Inter-Area Route Summarization - Area Range • By default ABRs do not summarize routes between areas. • In OSPF, an ABR will advertise networks in one area into another area. • If at least one component subnet exists (subnets that sit inside the range), then the ABR advertises the summary route as a Type 3 LSA. • If no component subnets exist, the ABR does not advertise the summary. • The ABR assigns a metric for the summary route's Type 3 LSA, by default, to match the best (lowest) metric amongst all component subnets. • The area range command can also explicitly set the cost of the summary. On the ABR (Summarizes routes before injecting them into different area) Router(config-router)# area area-idrangenetwork-address subnet-mask • area-id - Identifier of the area about which routes are to be summarized. (From area)

  42. 172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24 • Summarize Area 1 172.17.0.0 routes on Area 1 ABRs .

  43. 172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24 172.17. 0000 0001 . 0000 0000 172.17. 0000 0010 . 0000 0000 172.17. 0000 0011 . 0000 0000 172.17. 0000 0100 . 0000 0000 172.17. 0000 0101 . 0000 0000 172.17. 0000 0110 . 0000 0000 172.17. 0000 0111 . 0000 0000

  44. 172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24 172.17.0.0 255.255.248.0 (/21) 172.17. 0000 0001 . 0000 0000 172.17. 0000 0010 . 0000 0000 172.17. 0000 0011 . 0000 0000 172.17. 0000 0100 . 0000 0000 172.17. 0000 0101 . 0000 0000 172.17. 0000 0110 . 0000 0000 172.17. 0000 0111 . 0000 0000

  45. 172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24 router ospf 1 area 1 range 172.17.0.0 255.255.248.0

  46. Inter-Area Route Summarization - Area Range Before R2# show ip route 172.17.0.0/24 is subnetted, 7 subnets O IA 172.17.1.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.2.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.3.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.4.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.5.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.6.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 O IA 172.17.7.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0 After R2# show ip route O IA 172.17.0.0/21 [110/66] via 10.0.0.1, 00:10:17, Serial0/0

  47. 128.213.64.0 /24 … 128.213.95.0 /24 External Route Summarization - summary-address • When redistributing routes from other protocols into OSPF (later), each route is advertised individually in an external link state advertisement (LSA). • However, you can configure the Cisco IOS software to advertise a single route for all the redistributed routes that are covered by a specified network address and mask. • Doing so helps decrease the size of the OSPF link state database. On the ASBR only (Summarizes external routes before injecting them into the OSPF domain.) Router(config-router)# summary-address network-address subnet-mask

  48. Route Summarization 128.213.64.0 /24 … 128.213.95.0 /24 ASBR router ospf 1 summary-address 128.213.64.0 255.255.224.0 redistribute bgp 50 metric 1000 subnets (later)

  49. Default Routes

  50. Injecting Default Routes into OSPF • By default, 0.0.0.0/0 route is not propagated from the ASBR to other routers. • An autonomous system boundary router (ASBR) can be forced to generate a default route into the OSPF domain. • As discussed earlier, a router becomes an ASBR whenever routes are redistributed into an OSPF domain. • However, an ASBR does not, by default, generate a default route into the OSPF routing domain.

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