Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 11: OSPF

After completing this chapter, students will be able to: Describe the background and basic features of OSPF; identify and apply the basic OSPF configuration commands; describe, modify and calculate the metric used by OSPF; describe the Designated Router/Backup Designated Router (DR/BDR) election process in multiaccess networks; describe the uses of additional configuration commands in OSPF.
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Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 11: OSPFChapter 11: OSPFCCNA Exploration version 4.0 1Objectives • Describe the background and basic features of OSPF • Identify and apply the basic OSPF configuration commands • Describe, modify and calculate the metric used by OSPF • Describe the Designated Router/Backup Designated Router (DR/BDR) election process in multiaccess networks • Describe the uses of additional configuration commands in OSPF Học viện mạng Bách Khoa - Website: www.bkacad.com 2Introduction Học viện mạng Bách Khoa - Website: www.bkacad.com 3Introduction to OSPF Học viện mạng Bách Khoa - Website: www.bkacad.com 4Background of OSPF Background of 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 Học viện mạng Bách Khoa - Website: www.bkacad.com 5Single Area OSPF Concepts: OSPF terminology Học viện mạng Bách Khoa - Website: www.bkacad.com 6Single Area OSPF Concepts: OSPF terminology Học viện mạng Bách Khoa - Website: www.bkacad.com 7OSPF area Học viện mạng Bách Khoa - Website: www.bkacad.com 8OSPF Message Encapsulation Học viện mạng Bách Khoa - Website: www.bkacad.com 9OSPF Packet Types Học viện mạng Bách Khoa - Website: www.bkacad.com 10Hello Protocol Học viện mạng Bách Khoa - Website: www.bkacad.com 11Hello Protocol1. Discover OSPF neighbors and establish neighbor adjacencies.2. Advertise parameters on which two routers must agree to become neighbors.3. Elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks like Ethernet and Frame Relay. Học viện mạng Bách Khoa - Website: www.bkacad.com 12Hello Protocol• OSPF Hello Intervals – Usually multicast (224.0.0.5) – Sent every 30 seconds for NBMA segments – Sent every 10 seconds for Multi access network• OSPF Dead Intervals – This is the time that must be expired before the neighbor is considered down – Default time is 4 times the hello interval Học viện mạng Bách Khoa - Website: www.bkacad.com 13Hello Protocol Học viện mạng Bách Khoa - Website: www.bkacad.com 14Hello Protocol• Electing a DR and BDR –Designated Router (DR): DR is responsible for updating all other OSPF routers (called DROthers) –Backup Designated Router (BDR): This router takes over DR’s responsibilities if DR fails Học viện mạng Bách Khoa - Website: www.bkacad.com 15OSPF Link-state Updates• Purpose of a Link State Update (LSU): –Used to deliver link state advertisements• Purpose of a Link State Advertisement (LSA) –Contains information about neighbors & path costs Học viện mạng Bách Khoa - Website: www.bkacad.com 16OSPF Link-state Updates Học viện mạng Bách Khoa - Website: www.bkacad.com 17 Extra: How routing information is maintained when a failure is occurs Network 1 is down LSAs LSAs LSAsArea x 1. When a failure occurs in the network, such as a neighbor becomes unreachable 2. Link-state protocols flood LSAs using a special multicast address throughout an area. 3. Each link-state router takes a copy of the LSA, updates its link-state/topological database. 4. The link-state router will then forward the LSA to all neighboring devices. 5. LSAs cause every router within the area to recalculate routes. Because LSAs need to be flooded throughout an area Note: all routers within that area need to recalculate their routing tables ==> the number of link-state routers that can be in an area should be limited Học viện mạng Bách Khoa - Website: www.bkacad.com 18OSPF Algorithm Học viện mạng Bách Khoa - Website: www.bkacad.com 19Administrative Distance Học viện mạng Bách Khoa - Website: www.bkacad.com 20