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OSPF

OSPF. V1.1. Objectives. Have a general understanding of OSPF and its feature Grasp conceptions in OSPF Grasp the working principles of OSPF Grasp the configuration of OSPF Grasp the basic troubleshooting method of OSPF. Course Outline. OSPF overview OSPF terminology

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OSPF

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  1. OSPF V1.1

  2. Objectives • Have a general understanding of OSPF and its feature • Grasp conceptions in OSPF • Grasp the working principles of OSPF • Grasp the configuration of OSPF • Grasp the basic troubleshooting method of OSPF

  3. Course Outline • OSPF overview • OSPF terminology • OSPF working process • OSPF configuration

  4. OSPF introduction • OSPF (Open shortest path first), it is a link state protocol. • OSPF is a Interior Gateway Protocol (IGP）,it is used within an AS to decide route. • O in OSPF means the standard is open，not private routing protocol such as IGRP and EIGRP of CISCO.

  5. OSPF introduction(cont.) • RIP works by exchanging the whole route table with other routers, but OSPF exchange between each other link state information not route information. • Link-state protocol is the shortest path first protocol (S P F)-maintain a complex network topology database. • Link-state protocol can adapt to any size network as a dynamic routing protocol.

  6. OSPF Advantages • OSPF is a kind of link-state routing protocol，it has following advantages: • Choose path based on bandwidth • Fast convergence • Support VLSM and CIDR • Better hierarchical structure • Equal cost multipath

  7. OSPF Problems • Link-state routing protocols may have two problems： • At the first discovering process, link-state protocols will flood data on the line，thus weakening the data transferring capabilities. • Link-state routing protocols are sensitive to storage size and processor capability.

  8. OSPF in IP Packets • OSPF is a link-state routing protocol • Relies on IP packets for delivery of routing information • Uses protocol number 89 89 - OSPF 6 - TCP 17 - UDP Frame Payload C R C Frame Header IP Header Protocol Number Packet Payload

  9. OSPF Packet Header

  10. OSPF Packet Header (1) • Version——identify OSPF version • Type——identify OSPF data packet types as follows: • Hello packet : setup and maintain the relationship with neighbors • Database Description Packet (DDP): • Describe the content of network topology database • Link state request (LSR) • Request information from neighbor router from its network topology database • Link state update (LSU) • Reply to LSR packet • Link state Acknowledge (LSAck) • Acknowledge to LSU packet, making OSPF more reliable

  11. Packet Length——in bytes to identify the length of packet, including OSPF header; Router ID——identify the sender of the packet; Area ID——identify the area of the packet. Every OSPF packet is related to an area; Checksum——Check the content of the entire packet to find some mistakes in transmitting; Authentication Type——Including following types: 0 means no authentication,1 means using plain text to authenticate,2 means using MD5 algorithm. All the information exchanged in OSPF can be authenticated, authentication type can be configured for each area; Authentication data——data (including encapsulated upper layer data) with authentication information OSPF Packet Header(2)

  12. Course Outline • OSPF overview • OSPF terminology • OSPF working process • OSPF configuration

  13. OSPF Terminology • Router ID：Identify every router. Usually it is the highest IP address assigned to a router. If Loopback interface is used on the router, then router ID is the highest IP address among all the Loopback interface. • Interface：The connection between router and the network having only one IP address and mask. It is also called link. • Broadcast Network：Network that supports broadcasting such as Ethernet. • Non－Broadcast Network: Network that does not support broadcasting such as Frame Relay and X.25.

  14. Designated Router (DR) and Backup Designated Router (BDR)：In a broadcast network elect a DR and BDR to represent the network. This is to reduce the traffic on network. Adjacency：This relationship is formed between DR and undesignated router in broadcast network or NBMA network. Neighboring Routers：Routers which have interface to a common network. OSPF Terminology (Cont.)

  15. Neighbor Database：Including all the routers which have adjacency relationship. Link State Database：Including all the adjacency status between routers in the network. It shows the topology of a network. This database is the same for all the routers within an area. Routing Table：It is also called forwarding table, it is calculated with SPF algorithm based on the link state database. OSPF Terminology (Cont.)

  16. Router type: Different types of routers act different on controlling data coming in and going out. Router has a separate link state database for each area it connects to. Two routers that belong to one area has the same area link stare database. Link state advertisement (LSA): Describe the local status of a router. In OSPF network, there are 6 types of LSA. Route Summarization: Routes from one area, from another AS and from another kind of routing protocols can be combined together as a route summarization, if the design of the network is correct. OSPF Terminology (Cont.)

  17. Interfaces OSPF Terminology

  18. Neighbors Interfaces OSPF Terminology(Cont.)

  19. Neighbors Interfaces Cost = 10 Cost = 1785 Cost = 6 OSPF Terminology(Cont.)

  20. Neighbors Interfaces Area 1 Cost = 10 Area 0 Cost = 1785 Cost = 6 OSPF Terminology(Cont.)

  21. Autonomous System Neighbors Interfaces Area 1 Cost = 10 Area 0 Cost = 1785 Cost = 6 OSPF Terminology(Cont.)

  22. Autonomous System Neighbors Interfaces Area 1 Cost = 10 Area 0 Cost = 1785 Cost = 6 Neighborship Database Lists Neighbors OSPF Terminology(Cont.)

  23. Autonomous System Neighbors Interfaces Area 1 Cost = 10 Area 0 Cost = 1785 Cost = 6 Topology Database Lists All Routes Neighborship Database Lists Neighbors OSPF Terminology(Cont.)

  24. Autonomous System Neighbors Interfaces Area 1 Cost = 10 Area 0 Cost = 1785 Cost = 6 Neighborship Database Lists Neighbors Topology Database Lists All Routes Routing Table Lists Best Routes OSPF Terminology(Cont.)

  25. D E Hello Router ID Hello/dead intervals Neighbors Area-ID Router priority DR IP address BDR IP address Authentication password Stub area flag * C B A afadjfjorqpoeru 39547439070713 * Hello * * * Entry must match on neighboring routers Neighborship

  26. D E Hello Router ID Hello/dead intervals Neighbors Area-ID Router priority DR IP address BDR IP address Authentication password Stub area flag * C B A afadjfjorqpoeru 39547439070713 * Hello * * * Entry must match on neighboring routers Neighborship (cont.)

  27. Point-to-Point Broadcast Multiaccess X.25Frame Relay NonbroadcastMultiaccess OSPF Topology

  28. Hellos elect DR and BDR to represent segment Each router then forms adjacency with DR and BDR DR and BDR DR BDR

  29. Hello packets exchanged via IP multicast Router with highest OSPF priority elected Hello Electing DR and BDR P=3 P=2 DR BDR P=1 P=1 P=0

  30. Course Outline • OSPF overview • OSPF terminology • OSPF working process • OSPF configuration

  31. B A Establishing neighbor table(1) 172.16.5.1/24 E0 172.16.5.2/24 E1 Down State

  32. B A Establishing neighbor table(2) 172.16.5.1/24 E0 172.16.5.2/24 E1 Down State I am router ID 172.16.5.1 and I see no one. Init State Router B Neighbors List 172.16.5.1/24, int E1

  33. B A Establishing neighbor table(3) 172.16.5.1/24 E0 172.16.5.2/24 E1 A B Down State I am router ID 172.16.5.1 and I see no one. Init State Router B Neighbors List 172.16.5.1/24, int E1 I am router ID 172.16.5.2, and I see 172.16.5.1.

  34. B A Establishing neighbor table(4) 172.16.5.1/24 E0 172.16.5.2/24 E1 Down State I am router ID 172.16.5.1 and I see no one. Init State Router B Neighbors List 172.16.5.1/24, int E1 I am router ID 172.16.5.2, and I see 172.16.5.1. Router A Neighbors List 172.16.5.2/24, int E0 Two-Way State

  35. Establishing OSPF link state database(1) DR E0 172.16.5.1 E0 172.16.5.3 Exstart State afadjfjorqpoeru 39547439070713 I will start exchange because I have router ID 172.16.5.1. Hello No, I will start exchange because I have a higher router ID. afadjfjorqpoeru 39547439070713 Hello

  36. afadjfjorqpoeru 39547439070713 DBD Establishing OSPF link state database(2) DR E0 172.16.5.1 E0 172.16.5.3 Exstart State afadjfjorqpoeru 39547439070713 I will start exchange because I have router ID 172.16.5.1. Hello No, I will start exchange because I have a higher router ID. afadjfjorqpoeru 39547439070713 Hello Exchange State afadjfjorqpoeru 39547439070713 Here is a summary of my link-state database. DBD Here is a summary of my link-state database.

  37. Establishing OSPF link state database(3) DR DR E0 172.16.5.1 E0172.16.5.3 afadjfjorqpoeru 39547439070713 afadjfjorqpoeru 39547439070713 Thanks for the information! LSAck LSAck

  38. Establishing OSPF link state database(4) DR E0 172.16.5.1 E0172.16.5.3 afadjfjorqpoeru 39547439070713 afadjfjorqpoeru 39547439070713 Thanks for the information! LSAck LSAck Loading State afadjfjorqpoeru 39547439070713 I need the complete entry for network 172.16.6.0/24. LSR afadjfjorqpoeru 39547439070713 Here is the entry for network 172.16.6.0/24. LSU afadjfjorqpoeru 39547439070713 Thanks for the information! LSAck

  39. Establishing OSPF link state database(5) DR E0 172.16.5.1 E0172.16.5.3 afadjfjorqpoeru 39547439070713 afadjfjorqpoeru 39547439070713 Thanks for the information! LSAck LSAck Loading State afadjfjorqpoeru 39547439070713 I need the complete entry for network 172.16.6.0/24. LSR afadjfjorqpoeru 39547439070713 Here is the entry for network 172.16.6.0/24. LSU afadjfjorqpoeru 39547439070713 Thanks for the information! LSAck Full State

  40. OSPF Route Choice 10.1.1.0/24 10.2.2.0/24 10.3.3.0/24 B C A Cost=6 Cost=1 Cost=10 10.4.4.0/24 Topology Table Net Cost Out Interface 10.2.2.0 6 To0 10.3.3.0 7 To0 10.3.3.0 10 E0 This is the best route to 10.3.3.0.

  41. Router A tells all OSPF DRs on 224.0.0.6 1 x x Maintain routing information(1) Link-State Change DR LSU B A

  42. Router A tells all OSPF DRs on 224.0.0.6 DR tells others on 224.0.0.5 2 1 x x Maintain routing information(2) Link-State Change DR LSU LSU B A

  43. Router A tells all OSPF DRs on 224.0.0.6 DR tells others on 224.0.0.5 2 1 x x 3 Maintain routing information(3) Link-State Change DR LSU LSU B A LSU

  44. Router A tells all OSPF DRs on 224.0.0.6 DR tells others on 224.0.0.5 2 1 x x 3 Maintain routing information(4) Link-State Change DR LSU I need to update my routing table. 4 LSU B A LSU

  45. LSU Is entry inlink-statedatabase? LSA No Add to database Send LSAck to DR Flood LSA Run SPF to calculate new routing table End Maintain routing information(5)

  46. LSU Is entry inlink-statedatabase? Is seq. # the same? Ignore LSA LSA Yes Yes No Add to database Send LSAck to DR Flood LSA Run SPF to calculate new routing table End Maintain routing information(6)

  47. LSU LSA Is entry inlink-statedatabase? Is seq. # the same? Ignore LSA Yes Yes No No Add to database Is seq. # higher? Send LSAck to DR No Send LSU with newer information to source Flood LSA Run SPF to calculate new routing table End End Maintain routing information(7)

  48. LSU Is entry inlink-statedatabase? Is seq. # the same? LSA Ignore LSA Yes Yes No No Add to database A Is seq. # higher? Yes Send LSAck to DR No Send LSU with newer information to source Flood LSA Go to A Run SPF to calculate new routing table End End Maintain routing information(8)

  49. OSPF The SPF is running too Often For me to route I am only receiving LSA,no data OSPF OSPF OSPF OSPF My routing table is too big， I am running low on memory A problem in a large scale OSPF network

  50. Solution: Divide AREA Area 0 Area 1 Area 2 Autonomous System

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