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Day 12.2 enablingospf
The document provides an overview of the Open Shortest Path First (OSPF) routing protocol, highlighting its link-state nature, use of Dijkstra's algorithm, and hierarchical design to optimize routing. Key aspects include OSPF's metric system based on inverse bandwidth, configuration commands for implementing OSPF, and details about Designated Router (DR) and Backup Designated Router (BDR) elections. It also discusses the use of loopback interfaces for defining router IDs and testing purposes.
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Day 12.2 enablingospf
- 1. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-1 OPEN SHORTEST PATH FIRST (OSPF) Points to remember: OSPF is open protocol & is link state protocol. OSPF supports for VLSM & SUBNETTING. OSPF uses Dijkstra Algorithm to calculate the best paths. OSPF uses Cost (inverse of Bandwidth) as a metric. Sends updates when topology changes. OSPF is divided into hierarchical designs to minimize the routing table. It is divided in Areas & Autonomous System. Hello packets mechanism is used as well as link state advertisements packets are used to maintain the topology database. OSPF supports load balancing of up to six equal-cost paths to a single destination
- 2. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-2 OSPF metric OSPF uses cost. Cost is actually the inverse of the bandwidth of a link: the faster the speed of the connection, the lower the cost. The most preferred path is the one with the lowest cost. Cost = 10(power 8 ) /bandwidth (bps) OSPF supports load balancing of up to six equal-cost paths to a single destination.
- 3. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-3 OSPF Hierarchical Routing
- 4. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-4 REASONS FOR HEIRACHIAL DESIGNS To minimize the routing table. To speed up convergence. To confine the LSA flooding to the particular area only. Minimizes routing updates traffic.
- 5. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-5 Configuring Single Area OSPF g-router)#network net add wildcard mask area area-id • Assigns networks to a specific OSPF area Router(config)#router ospf process-id • Defines OSPF as the IP routing protocol
- 6. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-6 OSPF Configuration Example
- 7. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-7 Router#show ip ospf interface Verifying the OSPF Configuration • Displays area-ID and adjacency information Router#show ip protocols • Verifies that OSPF is configured Router#show ip route • Displays all the routes learned by the router Router#show ip ospf neighbor • Displays OSPF-neighbor information on a per-interface basis
- 8. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-8 OSPF debug commands Router#debug ip ospf events OSPF:hello with invalid timers on interface Ethernet0 hello interval received 10 configured 10 net mask received 255.255.255.0 configured 255.255.255.0 dead interval received 40 configured 30 Router# debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.117 aid:0.0.0.0 chk:6AB2 aut:0 auk: Router#debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.116 aid:0.0.0.0 chk:0 aut:2 keyid:1 seq:0x0
- 9. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-9 ELECTION OF DR & BDR The OSPF router with the highest priority becomes the DR for the segment. If there is a tie, the router with the highest router ID will become the DR. By default, all routers have a priority of 1 (priorities can range 0–255). If the DR fails, the BDR is promoted to DR and another router is elected as the BDR. When an OSPF router comes up, it forms adjacencies with the DR and the BDR on each multi-access segment that it is connected to. Any exchange of routing information is between these DR/BDR routers and the other OSPF neighbors on a segment (and vice versa). An OSPF router talks to a DR using the IP multicast address of 224.0.0.6. The DR and the BDR talk to all routers using the 224.0.0.5 multicast IP address.
- 10. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-10 Loopback interfaces A loopback interface is a logical, virtual interface on a router. By default, the router doesn’t have any loopback interfaces, but they can easily be created from 0 to to 2147483647. Reasons to create a loopback interface: 1) To assign a router ID to an OSPF router 2) To use for testing purposes, since this interface is always up
- 11. © 2002, CiscoSystems, Inc. All rights reserved. ICND v2.0—5-11
Editor's Notes
- #3 Purpose: The figure presents how IGRP load sharing improves throughput and increases reliability. Emphasize: Only feasible paths can be used for IGRP load sharing. Load-balancing methods vary according to the switching mode because the data structures for process switching, fast switching, and autonomous switching are all different. When process switching, the processor load-balances packet by packet. When fast, autonomous, or silicon switching, load balancing is done destination by destination. By default, the amount of variance is set to one, which results in equal-cost load balancing. You can use the default-metric command to change the default metric. Transition: The following pages describe how to configure the IGRP routing protocol.
- #6 Slide 1 of 2 Purpose: This figure explains how to use the router igrp and network commands to configure an IGRP process. Emphasize: Note that the AS keyword is required for IGRP. You can use multiple network commands to specify all networks that are to participate in the IGRP process. Only those networks specified will be published to other routers.
- #7 Purpose: The figure shows how the IGRP commands operate on the example network. Emphasize: An administrator only specifies directly connected networks that should be published to other routers. Without the network command, nothing is advertised. With a network command, the router will advertise every subnet within the Class A, B, or C network specified in the configuration.