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CHAPTER 5 Determining IP route

CHAPTER 5 Determining IP route. Static & Dynamic route Distance Vector routing protocol e.g. RIP, IGRP Link state routing protocol e.g. OSPF Hybrid routing protocol. Chapter Objective. On completion of this chapter, you will be able to perform the following tasks:

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CHAPTER 5 Determining IP route

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  1. CHAPTER 5Determining IP route Static & Dynamic route Distance Vector routing protocol e.g. RIP, IGRP Link state routing protocol e.g. OSPF Hybrid routing protocol 640-802 CCNA

  2. Chapter Objective 640-802 CCNA • On completion of this chapter, you will be able to perform the following tasks: • Distinguish the use and operation of static and dynamic routes • Identify concepts of distance vector IP routing protocols such as RIP and IGRP • Identify concepts of link state routing protocol

  3. What is a Routing Protocol? 10.120.2.0 172.16.1.0 Routing protocols are used between routers to determine paths and maintain routing tables. Once the path is determined a router can route a routed protocol. E0 S0 NetworkProtocol DestinationNetwork Exit Interface 172.17.3.0 10.120.2.0172.16.2.0172.17.3.0 E0S0S1 ConnectedRIPIGRP Routed Protocol: IPRouting protocol: RIP, IGRP 640-802 CCNA

  4. Autonomous Systems: Interior or Exterior Routing Protocols EGPs: BGP IGPs: RIP, IGRP Autonomous System 200 Autonomous System 100 • An autonomous system is a collection of networks under a common administrative domain • IGPs operate within an autonomous system • EGPs connect different autonomous systems 640-802 CCNA

  5. Administrative Distance: Ranking Routes I need to send a packet to Network E. Both router B and C will get it there. Which route is best? IGRPAdministrative Distance=100 Router B Router A RIPAdministrative Distance=120 E Router D Router C 640-802 CCNA

  6. Administrative Distance 640-802 CCNA

  7. Classes of Routing Protocols Distance Vector B A C D Hybrid Routing B Link State A C D 640-802 CCNA

  8. Distance Vector Routing Protocols B A C Distance—How farVector—In which direction D A D C B Routing Table Routing Table Routing Table Routing Table Pass periodic copies of routing table to neighbor routers and accumulate distance vectors 640-802 CCNA

  9. E0 S0 S0 S1 Sources of Information and Discovering Routes (1) 10.4.0.0 10.1.0.0 10.2.0.0 10.3.0.0 A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 0 E0 Routers discover the best path to destinations from each neighbor 640-802 CCNA

  10. E0 S0 S0 S1 S0 S1 S0 S0 Sources of Information and Discovering Routes (2) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 0 E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 10.1.0.0 1 Routers discover the best path to destinations from each neighbor 640-802 CCNA

  11. E0 S0 S0 S1 S0 S1 S0 S0 S0 Sources of Information and Discovering Routes (3) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 0 E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Routers discover the best path to destinations from each neighbor 640-802 CCNA

  12. Selecting Best Route with Metrics A IGRP Bandwidth Delay Load Reliability MTU 56 RIP Hop count T1 56 IPX T1 Ticks, hop count B Information used to select the best path for routing 640-802 CCNA

  13. Router A sends out this updated routing table after the next period expires Topology change causes routing table update Maintaining Routing Information Process to update this routing table Process to update this routing table A Updates proceed step-by-step from router to router 640-802 CCNA

  14. E0 S0 S0 S1 S0 S1 S0 S0 S0 Problem—Routing Loops (1) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 0 E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Each node maintains the distance from itself to each possible destination network 640-802 CCNA

  15. E0 S0 S0 S1 S0 S1 S0 S0 S0 Problem—Routing Loops (2) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 Down E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Each node maintains the distance from itself to each possible destination network 640-802 CCNA

  16. E0 S0 S0 S1 S0 S1 S0 S0 S0 Problem—Routing Loops (3) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 2 S0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Each node maintains the distance from itself to each possible destination network 640-802 CCNA

  17. E0 S0 S0 S1 S0 S1 S0 S0 S0 Problem—Routing Loops (4) 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 2 S0 1 10.3.0.0 10.4.0.0 3 10.2.0.0 1 S0 4 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Each node maintains the distance from itself to each possible destination network 640-802 CCNA

  18. E0 S0 S0 S1 S0 S1 S0 S0 S0 Symptom: Counting to Infinity 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 4 S0 1 10.3.0.0 10.4.0.0 5 10.2.0.0 1 S0 6 10.4.0.0 10.1.0.0 1 10.1.0.0 2 • Packets for network 10.4.0.0 bounce between routers A, B, and C • Hop count for network 10.4.0.0 counts to infinity 640-802 CCNA

  19. E0 S0 S0 S1 S0 S1 S0 S0 S0 Solution: Defining a Maximum 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 16 S0 1 10.3.0.0 10.4.0.0 16 10.2.0.0 1 S0 16 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Define a limit on the number of hops to prevent infinite loops 640-802 CCNA

  20. E0 S0 S0 S1 S0 S1 S0 S0 S0 Solution: Split Horizon 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 X X Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 0 E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 It is never useful to send information about a route back in the direction from which the original packet came 640-802 CCNA

  21. E0 S0 S0 S1 S0 S1 S0 S0 S0 Solution: Route Poisoning 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 0 10.4.0.0 Infinity E0 1 10.3.0.0 10.4.0.0 1 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Routers set the distance of routes that have gone down to infinity 640-802 CCNA

  22. E0 S0 S0 S1 S0 S1 S0 S0 S0 Solution: Poison Reverse 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 PoisonReverse Routing Table Routing Table Routing Table 10.1.0.0 0 10.2.0.0 0 10.3.0.0 0 S0 10.2.0.0 0 10.3.0.0 I 10.4.0.0 Infinity E0 1 10.3.0.0 10.4.0.0 Possibly down 10.2.0.0 1 S0 2 10.4.0.0 10.1.0.0 1 10.1.0.0 2 Poison Reverse overrides split horizon 640-802 CCNA

  23. Solution: Hold-Down Timers Network 10.4.0.0 is unreachable Update after hold-down Time 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Update after hold-down Time Network 10.4.0.0 is down then back up then back down Router keeps an entry for the network possibly downstate, allowing time for other routers to recompute for this topology change 640-802 CCNA

  24. Solution: Triggered Updates Network 10.4.0.0 is unreachable Network 10.4.0.0 is unreachable Network 10.4.0.0 is unreachable 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X A B C E0 S0 S0 S1 S0 E0 Router sends updates when a change in its routing table occurs 640-802 CCNA

  25. D E B A Implementing Solutions in Multiple Routes (1) Holddown 10.4.0.0 Poison Reverse X C Holddown Packet for Network 10.4.0.0 Packet for Network 10.4.0.0 Holddown 640-802 CCNA

  26. D E B A Implementing Solutions in Multiple Routes (2) 10.4.0.0 Link up! C 640-802 CCNA

  27. RIP Overview 19.2 kbps T1 T1 T1 • Maximum six paths (default = 4) • Hop count metric selects the path • Routes update every 30 seconds 640-802 CCNA

  28. RIP Configuration Router(config)# router rip • Starts the RIP routing process Router(config-router)# network network-number • Selects participating attached networks • The network number must be a major classfull network number 640-802 CCNA

  29. RIP Configuration Example E0 S2 S3 A S2 S3 E0 192.168.1.0 172.16.1.0 B C 10.1.1.1 172.16.1.1 10.1.1.2 10.2.2.2 192.168.1.1 10.2.2.3 router rip network 192.168.1.0 network 10.0.0.0 router rip network 172.16.0.0 network 10.0.0.0 router rip network 10.0.0.0 640-802 CCNA

  30. Verifying the Routing Protocol—RIP E0 S2 S3 A S2 S3 E0 192.168.1.0 172.16.1.0 B C 10.1.1.1 172.16.1.1 10.1.1.2 10.2.2.2 192.168.1.1 10.2.2.3 RouterA#ship protocols Routing Protocol is "rip" Sending updates every 30 seconds, next due in 0 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Key-chain Ethernet0 1 1 2 Serial2 1 1 2 Routing for Networks: 10.0.0.0 172.16.0.0 Routing Information Sources: Gateway Distance Last Update 10.1.1.2 120 00:00:10 Distance: (default is 120) 640-802 CCNA

  31. Displaying the IP Routing Table E0 S2 S3 A S2 S3 E0 192.168.1.0 172.16.1.0 B C 10.1.1.1 172.16.1.1 10.1.1.2 10.2.2.2 192.168.1.1 10.2.2.3 RouterA#ship route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR T - traffic engineered route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 2 subnets R 10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial2 C 10.1.1.0 is directly connected, Serial2 R 192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial2 640-802 CCNA

  32. debug ip rip Command E0 S2 S3 A S2 S3 E0 192.168.1.0 172.16.1.0 B C 10.1.1.1 172.16.1.1 10.1.1.2 10.2.2.2 192.168.1.1 10.2.2.3 RouterA# debug ip rip RIP protocol debugging is on RouterA# 00:06:24: RIP: received v1 update from 10.1.1.2 on Serial2 00:06:24: 10.2.2.0 in 1 hops 00:06:24: 192.168.1.0 in 2 hops 00:06:33: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:06:34: network 10.0.0.0, metric 1 00:06:34: network 192.168.1.0, metric 3 00:06:34: RIP: sending v1 update to 255.255.255.255 via Serial2 (10.1.1.1) 00:06:34: network 172.16.0.0, metric 1 640-802 CCNA

  33. Introduction to IGRP IGRP • More scalable than RIP • Sophisticated metric • Multiple-path support 640-802 CCNA

  34. IGRP Composite Metric 19.2 kbps 19.2 kbps Source Destination • Bandwidth (default) • Delay (default) • Reliability • Loading • MTU 640-802 CCNA

  35. IGRP Unequal Multiple Paths New Route Source Initial Route Destination • Maximum six paths (default = 4) • Within metric variance • Next-hop router closer to destination 640-802 CCNA

  36. Configuring IGRP (1) Router(config)#router igrpautonomous-system • Defines IGRP as the IP routing protocol Router(config-router)# network network-number • Selects participating attached networks 640-802 CCNA

  37. Configuring IGRP (2) Router(config-router)#variance multiplier • Control IGRP load balancing Router(config-router)# traffic-share { balanced | min } • Control how load-balanced traffic is distributed 640-802 CCNA

  38. IGRP Configuration Example Autonomous System = 100 E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 router igrp 100 network 172.16.0.0 network 10.0.0.0 router igrp 100 network 192.168.1.0 network 10.0.0.0 10.1.1.2 router igrp 100 network 10.0.0.0 640-802 CCNA

  39. Verifying the Routing Protocol—IGRP Autonomous System = 100 E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterA# ship protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 21 seconds …….. Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 10.0.0.0 172.16.0.0 Routing Information Sources: Gateway Distance Last Update 10.1.1.2 100 00:01:01 Distance: (default is 100) 640-802 CCNA

  40. Displaying the IP Routing Table Autonomous System = 100 E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterA#ship route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 …… Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 2 subnets I 10.2.2.0 [100/90956] via 10.1.1.2, 00:00:23, Serial2 C 10.1.1.0 is directly connected, Serial2 I 192.168.1.0/24 [100/91056] via 10.1.1.2, 00:00:23, Serial2 640-802 CCNA

  41. debug ipigrp transaction Command Autonomous System = 100 E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterA# debug ipigrp transactions IGRP protocol debugging is on RouterA# 00:21:06: IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:21:06: network 10.0.0.0, metric=88956 00:21:06: network 192.168.1.0, metric=91056 00:21:07: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1) 00:21:07: network 172.16.0.0, metric=1100 00:21:16: IGRP: received update from 10.1.1.2 on Serial2 00:21:16: subnet 10.2.2.0, metric 90956 (neighbor 88956) 00:21:16: network 192.168.1.0, metric 91056 (neighbor 89056) 640-802 CCNA

  42. debug ipigrp events Command Autonomous System = 100 E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterA# debug ipigrp events IGRP event debugging is on RouterA# 00:23:44: IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:23:44: IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. 00:23:44: IGRP: Total routes in update: 2 00:23:44: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1) 00:23:45: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes. 00:23:45: IGRP: Total routes in update: 1 00:23:48: IGRP: received update from 10.1.1.2 on Serial2 00:23:48: IGRP: Update contains 1 interior, 1 system, and 0 exterior routes. 00:23:48: IGRP: Total routes in update: 2 640-802 CCNA

  43. Updating Routing Information Example (1) Autonomous System = 100 E0 X S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterA# debug ipigrp trans 00:31:15: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0, changed state to down 00:31:15: IGRP: edition is now 3 00:31:15: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1) 00:31:15: network 172.16.0.0, metric=4294967295 00:31:16: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes. 00:31:16: IGRP: Total routes in update: 1 00:31:16: IGRP: broadcasting request on Serial2 00:31:16: IGRP: received update from 10.1.1.2 on Serial2 00:31:16: subnet 10.2.2.0, metric 90956 (neighbor 88956) 00:31:16: network 172.16.0.0, metric 4294967295 (inaccessible) 00:31:16: network 192.168.1.0, metric 91056 (neighbor 89056) 00:31:16: IGRP: Update contains 1 interior, 2 system, and 0 exterior routes. 00:31:16: IGRP: Total routes in update: 3 640-802 CCNA

  44. Updating Routing Information Example (2) Autonomous System = 100 E0 X S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterB#debugipigrp trans IGRP protocol debugging is on ……. 1d19h: IGRP: received update from 10.1.1.1 on Serial2 1d19h: network 172.16.0.0, metric 4294967295 (inaccessible) 1d19h: IGRP: edition is now 10 1d19h: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.2) 1d19h: subnet 10.2.2.0, metric=88956 1d19h: network 172.16.0.0, metric=4294967295 1d19h: network 192.168.1.0, metric=89056 1d19h: IGRP: sending update to 255.255.255.255 via Serial3 (10.2.2.2) 1d19h: subnet 10.1.1.0, metric=88956 1d19h: network 172.16.0.0, metric=4294967295 640-802 CCNA

  45. Updating Routing Information Example (3) E0 X S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 RouterB#ship route Gateway of last resort is not set I 172.16.0.0/16 is possibly down, routing via 10.1.1.1, Serial2 10.0.0.0/24 is subnetted, 2 subnets C 10.1.1.0 is directly connected, Serial2 C 10.2.2.0 is directly connected, Serial3 I 192.168.1.0/24 [100/89056] via 10.2.2.3, 00:00:14, Serial3 RouterB# ping 172.16.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: ..... Success rate is 0 percent (0/5) RouterB# 640-802 CCNA Chap05-45 640-802 CCNA

  46. Updating Routing Information Example (4) E0 S2 S2 S3 172.16.1.0 A 192.168.1.0 10.1.1.1 172.16.1.1 B C S3 E0 10.2.2.2 10.2.2.3 192.168.1.1 • RouterB# debug ipigrp transactions • RouterB# • 1d20h: IGRP: received update from 10.1.1.1 on Serial2 • 1d20h: network 172.16.0.0, metric 89056 (neighbor 1100) • RouterB# • RouterB# ship route • Gateway of last resort is not set • I 172.16.0.0/16 is possibly down, routing via 10.1.1.1, Serial2 • 10.0.0.0/24 is subnetted, 2 subnets • C 10.1.1.0 is directly connected, Serial2 • C 10.2.2.0 is directly connected, Serial3 • I 192.168.1.0/24 [100/89056] via 10.2.2.3, 00:00:18, Serial3 • RouterB#ping 172.16.1.1 • Type escape sequence to abort. • Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: • !!!!! • Success rate is 100 percent (5/5), round-trip min/avg/max = 32/38/48 ms 640-802 CCNA Chap05-46 640-802 CCNA

  47. B C A D Link-State Routing Protocols Link-State Packets Topological Database Routing Table SPF Algorithm Shortest Path First Tree After initial flood, pass small event-triggered link-state updates to all other routers 640-802 CCNA

  48. OSPF Overview (1) • Open Shortest Path First (OSPF) protocol is a link state protocol. • Its newest implementation, version 2 • Advantage of OSPF • Uses the SPF algorithm, developed by Dijkstra. • Provide a loop-free topology. • Fast convergence with triggered. • Incremental updates via Link State Advertisements (LSAs). • Classless protocol and allows for a hierarchical design with • VLSM and route summarization. 640-802 CCNA

  49. OSPF Overview (2) 640-802 CCNA • Disadvantage • Requires more memory to hold the list of adjacency (OSPF neighbors) topology • Requires extra CPU processing. Especially first turn on the routers and they are initially building the adjacency and topology tables. • For large networks, require to break up the network into different areas.

  50. OSPF Area 640-802 CCNA

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