Chapter 11 - OSPF CCNA docx

1 Chapter 11 - OSPF CCNA Exploration 4.0 Học viện mạng Bách Khoa - Website: www.bkacad.com 2 Objectives • 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 3 Introduction Học viện mạng Bách Khoa - Website: www.bkacad.com 4 Background of OSPF • Began in 1987. • 1989 OSPFv1 released in RFC 113. This version was experimental & never deployed • 1991 OSPFv2 released in RFC 1247. • 1998 OSPFv2 updated in RFC 2328. • 1999 OSPFv3 published in RFC 2740. Introduction to OSPF Học viện mạng Bách Khoa - Website: www.bkacad.com 5 OSPF Message Encapsulation • OSPF packet type – There exist 5 types. • OSPF packet header – Router ID. – Area ID. – Type code(packet type). • IP packet header – Source IP address. – Destination IP address. – Protocol field (set to 89 ). Introduction to OSPF Học viện mạng Bách Khoa - Website: www.bkacad.com 6 Introduction to OSPF OSPF Message Encapsulation • Data link frame header – Source MAC address. – Destination MAC address. Học viện mạng Bách Khoa - Website: www.bkacad.com 7 OSPF Packet Types OSPF PACKET TYPE DESCRIPTION 1: HELLO Discovers neighbors & builds ADJACENCY W/ NEIGHBORS 2: DATABASE DESCRIPTION Checks for database synchronization between routers 3: LINK STATE REQUEST REQUESTS SPECIFIC LINK STATE DATABASE information from router to router 4: LINK STATE UPDATE TRANSPORTS LINK STATE records 5: LINK STATE ACKNOWLEDGEMENT ACKNOWLEDGES RECEIPT OF other packet types Học viện mạng Bách Khoa - Website: www.bkacad.com 8 Hello Protocol • OSPF Hello Packet – Purpose of Hello Packet  Discover OSPF neighbors & establish adjacencies.  Advertise guidelines on which routers must agree to become neighbors.  Used by multi-access networks to elect a designated router(DR) and a backup designated router(BDR). Học viện mạng Bách Khoa - Website: www.bkacad.com 9 OSPF Hello Packet Học viện mạng Bách Khoa - Website: www.bkacad.com 10 • Hello Packets continued – Router ID of transmitting router. – Sent every 10 seconds on multiaccess & point to point serial link. • OSPF Hello Intervals – Usually multicast (224.0.0.5). – Sent every 30 seconds for NBMA segments. • 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. OSPF timers [...]... OSPF on a router use the following command – R1(config)#router ospf process-id – Process id • A locally significant number between 1 and 65535 • Does not have to match other OSPF routers Học viện mạng Bách Khoa - Website: www.bkacad.com 19 Basic OSPF Configuration • RA(config-router)#network network-address wildcardmask area area-id – wildcard mask - the inverse of the subnet mask – area-id • Area-id... www.bkacad.com 22 Basic OSPF Configuration OSPF Router ID • Router ID & Loopback addresses – Highest loopback address will be used as router ID if router-id command isn’t used – Advantage: loopback interface cannot fail  OSPF stability • The OSPF router-id command – Introduced in IOS 12.0 – Command syntax • Router(config)#router ospf process-id • Router(config-router)#router-id ip-address • Modifying... Router#clear ip ospf process Học viện mạng Bách Khoa - Website: www.bkacad.com 23 Show ip ospf neighbor command • Neighbor ID - The router ID of the neighboring router • Pri - The OSPF priority of the interface This is discussed in a later • • • • section State - The OSPF state of the interface FULL state means that the router and its neighbor have identical OSPF link-state databases OSPF states are... refers to the OSPF area • OSPF area is a group of routers that share link state information Học viện mạng Bách Khoa - Website: www.bkacad.com 20 OSPF Router ID Find Router ID Học viện mạng Bách Khoa - Website: www.bkacad.com 21 Basic OSPF Configuration OSPF Router ID • Commands used to verify current router ID – Show ip protocols – Show ip ospf – Show ip ospf interface Học viện mạng Bách Khoa - Website:... www.bkacad.com 15 Basic OSPF configuration Học viện mạng Bách Khoa - Website: www.bkacad.com 16 Example Lab Topology • Topology used for this chapter – Discontiguous IP addressing scheme – Since OSPF is a classless routing protocol the subnet mask is configured in Học viện mạng Bách Khoa - Website: www.bkacad.com 17 Addressing Học viện mạng Bách Khoa - Website: www.bkacad.com 18 Enable OSPF The router ospf command... Bách Khoa - Website: www.bkacad.com 25 Reasons of no adjacency • Two routers may not form an OSPF adjacency if: – The subnet masks do not match, causing the routers to be on separate networks – OSPF Hello or Dead Timers do not match – OSPF Network Types do not match – There is a missing or incorrect OSPF network command Học viện mạng Bách Khoa - Website: www.bkacad.com 26 Verifying OSPF - Additional... 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 Học viện mạng Bách Khoa - Website: www.bkacad.com 27 Show ip protocols Học viện mạng Bách Khoa - Website: www.bkacad.com 28 Show ip ospf. .. bandwidth – Commands used to modify bandwidth value  Router(config-if)#bandwidth bandwidth-kbps  R1(config)#interface serial 0/0/0  R1(config-if)#ip ospf cost 1562 Học viện mạng Bách Khoa - Website: www.bkacad.com 35 Basic OSPF Configuration Modifying the Cost of the link • Difference between bandwidth command & the ip ospf cost command: – Ip ospf cost command • Sets cost to a specific value – Bandwidth... Bách Khoa - Website: www.bkacad.com 29 Show ip ospf interface Học viện mạng Bách Khoa - Website: www.bkacad.com 30 Show ip route - Examining the routing table • Use the show ip route command to display the routing table – “O’ at the beginning of a route indicates that the router source is OSPF – Note OSPF does not automatically summarize at major network boundaries Học viện mạng Bách Khoa - Website:... 31 OSPF Metric • OSPF uses cost as the metric for determining the best route – Best route ~ lowest cost – Cost: 108 / bandwidth – Reference bandwidth • Defaults to 100Mbps • Can be modified using auto-cost referencebandwidth command Học viện mạng Bách Khoa - Website: www.bkacad.com 32 OSPF Metric • COST of an OSPF route – Is the accumulated value from one router to the next Học viện mạng Bách Khoa - . 1 Chapter 11 - OSPF CCNA Exploration 4.0 Học viện mạng Bách Khoa - Website: www.bkacad.com 2 Objectives • Describe the background and basic features of OSPF • Identify and apply the basic OSPF. other OSPF routers. Học viện mạng Bách Khoa - Website: www.bkacad.com 20 Basic OSPF Configuration • RA(config-router)#network network-address wildcard- mask area area-id – wildcard mask - the. table. Introduction to OSPF Học viện mạng Bách Khoa - Website: www.bkacad.com 14 OSPF Administrative Distance • Default Administrative Distance for OSPF is 110 Học viện mạng Bách Khoa - Website: www.bkacad.com