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OSPF - OSPF CCNA Exploration Semester 2 Chapter 11 23 Sep...

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23 Sep 2009 S Ward Abingdon and Witney College 1 OSPF CCNA Exploration Semester 2 Chapter 11
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23 Sep 2009 S Ward Abingdon and Witney College 2 Topics Background and features of OSPF Configure basic OSPF OSPF metric Designated router/backup designated router elections Default information originate
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23 Sep 2009 S Ward Abingdon and Witney College 3 RIP v1 RIP v2 IGRP EIGRP Routing protocols Interior Exterior Distance vector Link state OSPF IS-IS EGP BGP
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23 Sep 2009 S Ward Abingdon and Witney College 4 OSPF background Developed by IETF to replace RIP Better metric Fast convergence Scales to large networks by using areas
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23 Sep 2009 S Ward Abingdon and Witney College 5 OSPF packets 0x01 Hello establishes and maintains adjacency 0x02 Database Description (DBD) summary of database for other routers to check 0x03 Link State Request (LSR) use to request more detailed information 0x04 Link State Update (LSU) reply to LSR and send new information 0x05 Link State Acknowledgement (LSAck)
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23 Sep 2009 S Ward Abingdon and Witney College 6 OSPF encapsulation Data link frame header IP packet header OSPF packet header Data MAC destination address Multicast 01-00-5E-00-00-05 or 01-00-5E-00-00-06
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23 Sep 2009 S Ward Abingdon and Witney College 7 OSPF encapsulation Data link frame header IP packet header OSPF packet header Data IP destination address Multicast 224.0.0.5 or 224.0.0.6 Protocol field 89
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23 Sep 2009 S Ward Abingdon and Witney College 8 OSPF encapsulation Data link frame header IP packet header OSPF packet header Data Type code for packet type (0x01 etc) Router ID and Area ID
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23 Sep 2009 S Ward Abingdon and Witney College 9 Hello, OSPF packet type 1 Discover OSPF neighbours and establish adjacencies. Advertise parameters on which two routers must agree to become neighbors. Elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks like Ethernet and Frame Relay.
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23 Sep 2009 S Ward Abingdon and Witney College 10 Fields in Hello packet Type (=1), Router ID, Area ID Subnet mask of sending interface Hello Interval, Dead Interval Router Priority: Used in DR/BDR election Designated Router (DR): Router ID of the DR, if any Backup Designated Router (BDR): Router ID of the BDR, if any List of Neighbors: lists the OSPF Router ID of the neighboring router(s)
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23 Sep 2009 S Ward Abingdon and Witney College 11 Sending Hellos By default, OSPF Hello packets are sent every 10 seconds on multiaccess and point- to-point segments and every 30 seconds on non-broadcast multiaccess (NBMA) segments (Frame Relay, X.25, ATM). In most cases, OSPF Hello packets are sent as multicast to 224.0.0.5. Router waits for Dead interval before declaring the neighbor "down." Default is four times the Hello interval.
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23 Sep 2009 S Ward Abingdon and Witney College 12 Matching Before two routers can form an OSPF neighbour adjacency, they must agree on three values: Hello interval, Dead interval, Network type (e.g. point to point, Ethernet, NBMA.)
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23 Sep 2009 S Ward Abingdon and Witney College 13
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