1. Konsep Routing dan Protokol

2. Pengenalan

3. Latarbelakang Open Shortest Path First (OSPF)
Began in 1987
1989 OSPFv1 released in RFC 1131
This version was experimental & never deployed
1991 OSPFv2 released in RFC 1247
1998 OSPFv2 updated in RFC 2328
1999 OSPFv3 published in RFC 2740

5. Pengkapsulan Mesej OSPF (Message Encapsulation)
Data link frame header
Contains - Source MAC address
Destination MAC address
IP packet header
Contains - Source IP address,
Destination IP address, &
Protocol field set to 89
OSPF packet header
Contains - Router ID and area ID, &
Type code for OSPF packet type
OSPF packet type - One of 5 types

7. Jenis-jenis Paket OSPF
Nama Paket
Keterangan 1
Hello 2
Penerangan Database (DBD)
semak pangkalan data untuk penyelerakan(sychronization) antara router 3
Link-State Request (LSR)
Memohon rekod link-state khusus dari router ke router 4
Link-State Update (LSU)
Menghantar rekod link-state yang diminta secara spesifik 5
Link-state Acknowledgement (LSAck)
Mengesahkan jenis-jenis paket lain

8. Tujuan Packet Hello OSPF
mencari rakan/jiran (neighbors) OSPF & menubuhkan bersebelahan
mengemukakan garis panduan yang perlu diterima oleh router untuk menjadi neighbors
Digunakan sebagai rangkaian pelbagai akses (multi-access networks) untuk memilih router (designated router) dan router sandaran (backup designated router) yang ditetapkan/direkabentuk
DR designated router
BDR backup de signated router

11. OSPF Paket Hello (Hello Packets)
-kandungan paket jenis Hello
-ID router untuk menghantar router
OSPF Hello Selang (OSPF Hello Intervals)
biasanya multicast ( )
Dihantar setiap 30 saat untuk setiap segmen NBMA
OSPF Selang Mati (OSPF Dead Intervals)
adalah masa yang mesti diketahui umum sebelum neighbor dianggap down
Masa lalai (Default time) adalah 4 kali “hello” interval

13. OSPF
Protokol paket Hello mengandungi maklumat yang digunakan dalam pemilihan
-Designated Router (DR)
Router yang bertanggungjawab untuk mengemaskinikan semua router OSPF lain
-Backup Designated Router (BDR)
Router ini mengambil alih tanggungjawab DR jika DR gagal

14. OSPF Link-state Updates
Tujuan Link State Update (LSU) -
Digunakan untuk membuat sebaran Link State
Tujuan Link State Advertisement (LSA) -
Mengandungi maklumat tentang neighbors & path costs

16. Algorithma OSPF
Router OSPF membina & mengawal pangkalan data link-state yang mengandungi LSA yang diterima daripada router lain
Maklumat yang terdapat di dalam pangkalan data digunakan apabila melaksanakan algoritma SPF dijkstra
algorithma SPF digunakan untuk membina SPF tree
SPF tree digunakan untuk mengisi jadual routing

18. Administrative Distance

19. Pengesahan (Authentication) OSPF
Tujuannya adalah untuk menyulitkan & mengesahkan maklumat routing
Ia adalah konfigurasi antaramuka spesifik (interface specific)
Routers hanya akan terima maklumat routing dari router lain yang dikonfigurasi dengan katakunci (password) atau pengesahan maklumat yang sama sahaja

20. Topologi Discontiguous IP addressing scheme
Since OSPF is a classless routing protocol the subnet mask is configured in each router

21. The router OSPF command
To enable OSPF on a router use the following command
R1(config)#router ospf process-id
Where the Process id
Is a locally significant number between 1 and 65535

22. OSPF network command Requires: network address
wildcard – NOT a subnet mask
area-id - refers to the OSPF area.
The OSPF area is a group of routers sharing link state information
Router(config-router)#network network-address wildcard-ask area area-id

23. Asas Konfigurasi OSPF Router ID
IP address digunakan untuk kenalpasti router
Tiga kriteria untuk memperolehi ID router:
Router-id IP address
Loopback IP address
Highest IP address on any active interface

24. Commands used to verify current router ID
Show ip protocols
Show ip ospf
Show ip ospf interface

25. Commands used to verify current router ID

26. Arahan yang digunakan untuk mengesahkan ID router semasa
Show ip protocol
show ip ospf
Show ip ospf interface

27. Commands used to verify current router ID

28. OSPF Router ID Router ID & Loopback addresses
-Highest loopback address will be used as router ID if router-id command isn’t used
-Advantage of using loopback address
the loopback interface cannot fail  OSPF stability
The OSPF router-id command
Introduced in IOS 12.0
Command syntax
Router(config)#router ospfprocess-id
Router(config-router)#router-idip-address
Modifying the Router ID
Use the command Router#clear ip ospf process

29. Verifying OSPF
Use the show ip ospf command to verify & trouble shoot OSPF networks
Command will display the following:
Neighbor adjacency
-No adjacency indicated if:
Neighboring router’s Router ID is not displayed
A state of full is not displayed
-Consequence of no adjacency:
No link state information exchanged
Inaccurate SPF trees & routing tables result

30. Verifying OSPF - Additional Commands
Description
Show ip protocols
Displays OSPF process ID, router ID, networks router is advertising & administrative distance
Show ip ospf
Displays OSPF process ID, router ID, OSPF area information & the last time SPF algorithm calculated
Show ip ospf interface
Displays hello interval and dead interval

31. Examining the routing table
Use the show ip route command to display the routing table
NOTE - OSPF does not automatically summarize at major network boundaries

32. OSPF Metric
OSPF uses cost as the metric for determining the best route
-The best route will have the lowest cost
-Cost is based on bandwidth of an interface
Cost is calculated using the formula / bandwidth
-Reference bandwidth
defaults to 100Mbps
can be modified using the auto-cost reference-bandwidth command

34. OSPF Metric
Biasanya kelajuan rangkaian sebenar adalah berbeza jika dibandingkan dengan default bandwidth
Ini menjadikan ia amat penting bahawa nilai bandwidth mencerminkan kelajuan sebenar pautan
Alasannya:
Jadual routing mempunyai maklumat laluan terbaik
Arahan show interface akan memaparkan antaramuka bandwidth
-kebanyakan serial link default kepada 1.544Mbps = T1

36. Modifying the Cost of a link
Kedua-dua belah pautan bersiri sepatutnya dikonfigurasi dengan bandwidth yang sama
Dua arahan yang digunakan untuk mengubahsuai bandwidth:
Bandwidth command
Example:
R1(config-if)#bandwidth bandwidth-kbps
ip ospf cost command – allows you to directly specify interface cost
-Example: R1(config)#interface serial 0/0/0
R1(config-if)#ip ospf cost 1562

37. Perubahan (Changing) Bandwidth

38. Changing Cost

39. Modifying the Cost of the link
Perbezaan di antara arahan bandwidth & arahan kos IP OSPF
Bandwidth
Link cost is calculated
IP OSPF cost
Sets cost to a specific value

42. Challenges in Multi-access Networks
OSPF defines five network types:
Point-to-point
Broadcast Multi-access
Non-broadcast Multi-access (NBMA)
Point-to-multipoint
Virtual links

43. Two challenges presented by multi-access networks
Multiple adjacencies
Extensive LSA flooding

44. OSPF in Multiaccess Networks
Extensive flooding of LSAs
For every LSA sent out there must be an acknowledgement of receipt sent back to transmitting router.
consequence: lots of bandwidth consumed and chaotic traffic

45. OSPF in Multiaccess Networks
Solution to LSA flooding issue is the use of
Designated router (DR)
Backup designated router (BDR)
DR & BDR selection
Routers are elected to send & receive LSA
Sending & Receiving LSA
DRothers send LSAs via multicast address to DR & BDR
DR forward LSA via multicast address to all other routers

46. OSPF in Multiaccess Networks

47. DR/BDR Election Process
DR/BDR elections DO NOT occur in point to point networks

48. OSPF in Multiaccess Networks
DR/BDR elections will take place on multiaccess networks as shown below

49. OSPF in Multi-access Networks
Kriteria untuk membuat pilihan samada DR/BDR
DR: Router with the highest OSPF interface priority.
BDR: Router with the second highest OSPF interface priority.
If OSPF interface priorities are equal, then the
Highest router ID is used to break the tie.

50. OSPF in Multi-access Networks

51. OSPF in Multi-access Networks

52. OSPF in Multi-access Networks

53. Timing of DR/BDR Election
Ia berlaku apabila router pertama mempunyai antaramuka yang membolehkan rangkaian multiaccess
DR yang dipilih akan kekal sebagai DR sehingga salah satu daripada berikut berlaku:
-Kegagalan DR (DR fails).
-Proses OSPF ke atas DR yang gagal.
-multi-access interface on the DR fails.

54. Manipulating the election process
Proses memanipulasikan pemilihan DR & BDR boleh dilakukan dengan membuat salah satu daripada berikut:
Boot up the DR first, followed by the BDR, and then boot all other routers, OR
Shut down the interface on all routers, followed by a no shutdown on the DR, then the BDR, and then all other routers.

55. Manipulating the DR/BDR election process continued
Use the ip OSPF priority interface command.
Example: Router(config-if)#ip ospf priority { }
Priority number range 0 to 255
0 means the router cannot become the DR or BDR
1 is the default priority value

56. Redistributing an OSPF Default Route
Topology including an ISP
Router connected to ISP
Called an autonomous system border router
Used to propagate a default route
Example:
R1(config)#ip route loopback 1
This requires the use of the default-information originate command
R1(config-router)#default-information originate

57. Fine-Tuning OSPF
Oleh kerana, kelajuan link agak cepat, nilai-nilai lebar jalur (bandwidth) rujukan mungkin perlu ditukar.
Berikut adalah arahan untuk auto-cost reference-bandwidth
Contoh:
R1(config-router)#auto-cost reference-bandwidth 10000

58. Fine-Tuning OSPF

59. Fine-Tuning OSPF

60. Fine-Tuning OSPF: Modifying timers
Reason:
Faster detection of network failures
Manually modifying Hello & Dead intervals
Router(config-if)#ip ospf hello-interval  seconds
Router(config-if)#ip ospf dead-interval seconds
NOTE: Hello & Dead intervals must be the same between neighbors

61. Ringkasan RFC 2328 describes OSPF link state concepts and operations
OSPF Characteristics
Is a commonly deployed link state routing protocol
Employs DRs & BDRs on multi-access networks
DRs & BDRs are elected
DR & BDRs are used to transmit and receive LSAs
Uses 5 different packet types:
1: HELLO
2: DATABASE DESCRIPTION
3: LINK STATE REQUEST
4: LINK STATE UPDATE
5: LINK STATE ACKNOWLEDGEMENT

62. Summary OSPF Characteristics Configuration Metric = cost
Lowest cost = best path
Configuration
To enable OSPF
R1(config)#router ospf process-id
use the network command to define which interfaces will participate in a given OSPF process
Router(config-router)#network network-address wildcard area area-id

63. Summary Verifying OSPF configuration Show ip interface brief
Use the following commands:
Show ip interface brief
show ip route
show ip ospf neighbor
show ip protocol
show ip ospf interface

64. The END
Chapter 11 OSPF