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CCNA: Cisco Certified Network Associate Study Guide

CCNA: Cisco Certified Network Associate Study Guide. CHAPTER 6: Enhanced IGRP (EIGRP) and Open Shortest Path First (OSPF). The CCNA exam topics covered in this chapter include the following:. Planning & Designing • Select an appropriate routing protocol based on user requirements

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CCNA: Cisco Certified Network Associate Study Guide

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  1. CCNA: Cisco Certified Network Associate Study Guide CHAPTER 6: Enhanced IGRP (EIGRP) and Open Shortest Path First (OSPF)

  2. The CCNA exam topics covered in this chapter include the following: • Planning & Designing • • Select an appropriate routing protocol based on user requirements • • Design a simple internetwork using Cisco technology • Implementation & Operation • • Configure routing protocols given user requirements

  3. Enhanced IGRP supports: Rapid convergence Reduced bandwidth usage Multiple network-layer support Uses Diffused Update Algorithm (DUAL) to select loop-free routes and enable fast convergence Up to six unequal paths to a remote network (4 by default) What Is Enhanced IGRP (EIGRP)? IP RoutingProtocols IP RoutingProtocols AppleTalk Routing Protocol EnhancedIGRP AppleTalk Routing Protocol IPX RoutingProtocols IPX RoutingProtocols

  4. Comparing EIGRP and IGRP • Similar metric • Same load balancing • Improved convergence time • Reduced network overhead • Maximum hop count of 255 (100 default) • EIGRP can differentiate between internal and external routes

  5. Enhanced IGRP EIGRP EIGRP EIGRP for IP • No updates. Route updates sent only when a change occurs – multicast on 224.0.0.10 • Hello messages sent to neighbors every 5 seconds (60 seconds in most WANs) hello

  6. Topology Table—IP Destination 1 Successor Destination 1 Feasible Successor Routing Table—IP Destination 1 Successor EIGRP Terminology Neighbor Table—IP Next Hop Interface Router Note: A feasible successor is a backup route and stored in the Topology table

  7. Enhanced IGRP EIGRP EIGRP EIGRP Tables • The neighbor table and topology table are held in ram and are maintained through the use of hello and update packets. hello To see all feasible successor routes known to a router, use the show ip eigrp topology command

  8. Topology Table—IP Destination 1 Successor Destination 1 Feasible Successor Routing Table—IP Destination 1 Successor Successor routes • Successor route is used by EIGRP to forward traffic to a destination • A successor routes may be backed up by a feasible successor route • Successor routes are stored in both the topology table and the routing table

  9. EIGRP uses a composite metric to pick the best path: bandwidth and delay of the line EIGRP (and IGRP) can load balance across six unequal cost paths to a remote network (4 by default) Choosing Routes IP IP A B 19.2 AppleTalk AppleTalk T1 T1 IPX IPX T1 C D

  10. Configuring EIGRP for IP AS=10 C A B 172.16.10.0 10.110.1.0 192.168.0.0 192.168.0.0 Router(config)#router eigrp 10Router(config-router)#network 10.0.0.0Router(config-router)#network 172.16.0.0 Enable EIGRP Assign networks If you use the same AS number for EIGRP as IGRP, EIGRP will automatically redistribute IGRP into EIGRP

  11. Redistribution Redistribution is translating one type of routing protocol into another. EIGRP IGRP Router B Router D Router A Router C IGRP and EIGRP translate automatically, as long as they are both using the same AS number

  12. Route Path Assuming all default parameters, which route will RIP (v1 and v2) take, and which route will EIGRP take? T1 T1 56K 10BaseT 100BaseT 100BaseT

  13. Displays the neighbors discovered by IP Enhanced IGRP Displays the IP Enhanced IGRP topology table Displays current Enhanced IGRP entries in the routing table Displays the parameters and current state of the active routing protocol process Displays the number of IP Enhanced IGRP packets sent and received Verifying Enhanced IGRP Operation show ip eigrp neighbors Router# show ip eigrp topology Router# show ip route eigrp Router# show ip protocols Router# show ip eigrp traffic Router#

  14. Show IP Route P1R1#sh ip route [output cut] Gateway of last resort is not set D 192.168.30.0/24 [90/2172] via 192.168.20.2,00:04:36, Serial0/0 C 192.168.10.0/24 is directly connected, FastEthernet0/0 D 192.168.40.0/24 [90/2681] via 192.168.20.2,00:04:36, Serial0/0 C 192.168.20.0/24 is directly connected, Serial0/0 D 192.168.50.0/24 [90/2707] via 192.168.20.2,00:04:35, Serial0/0 P1R1# -D is for “Dual” -[90/2172] is the administrative distance and cost of the route. The cost of the route is a composite metric comprised from the bandwidth and delay of the line

  15. Introducing OSPF • Open standard • Shortest path first (SPF) algorithm • Link-state routing protocol (vs. distance vector) • Can be used to route between AS’s

  16. Consists of areas and autonomous systems Minimizes routing update traffic Supports VLSM Unlimited hop count OSPF Hierarchical Routing

  17. Link State Vs. Distance Vector Link State: • Provides common view of entire topology • Calculates shortest path • Utilizes event-triggered updates • Can be used to route between AS’s • Distance Vector: • Exchanges routing tables with neighbors • Utilizes frequent periodic updates

  18. Types of OSPF Routers Area 1 Backbone Area 0 Area 2 ABR and BackboneRouter Backbone/InternalRouters InternalRouters InternalRouters ASBR andBackbone Router ABR and BackboneRouter • External AS

  19. Configuring Single Area OSPF Router(config)#router ospf process-id Defines OSPF as the IP routing protocol Note: The process ID is locally significant and is needed to identify a unique instance of an OSPF database Router(config-router)#network address mask area area-id Assigns networks to a specific OSPF area

  20. R2 Area 0 R1 10.1.3.0 R3 10.5.5.0 10.1.1.0 10.1.2.0 OSPF Example

  21. Verifying the OSPF Configuration 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 interface Displays area-ID and adjacency information Router#show ip ospf neighbor Displays OSPF-neighbor information on a per-interface basis

  22. OSFP Neighbors • OSPF uses hello packets to create adjacencies and maintain connectivity with neighbor routers • OSPF uses the multicast address 224.0.0.5 Hello? 224.0.0.5 • Hello packets provides dynamic neighbor discovery • Hello Packets maintains neighbor relationships • Hello packets and LSA’s from other routers help build and maintain the topological database

  23. OSPF Terminology • Neighbor • Adjacency Neighbors ABR DR Adjacencies Non-DR Cost=6 BDR

  24. Router ID (RID) Each router in OSPF needs to be uniquely identified to properly arrange them in the Neighbor tables.

  25. OSPF sends Hellos which elect DRs and BDRs Router form adjacencies with DRs and BDRs in a multi-access environment Electing the DR and BDR Multicast Hellos are sent and compared Router with Highest Priority is Elected as DR Router with 2nd Highest Priority is Elected as BDR

  26. Configuring Loopback Interfaces Router ID (RID): • Number by which the router is known to OSPF • Default: The highest IP address on an active interface at the moment of OSPF process startup • Can be overridden by a loopback interface: Highest IP address of any active loopback interface – also called a logical interface

  27. Interface Priorities What is the default OSPF interface priority? Router# show ip ospf interface ethernet0/0 Ethernet0 is up, line protocol is up Internet Address 192.168.1.137/29, Area 4 Process ID 19, Router ID 192.168.1.137, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 192.168.1.137, Interface address 192.168.1.137 No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:06 Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 0, maximum is 0 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s)

  28. Ensuring your DR What options can you configure that will ensure that R2 will be the DR of the LAN segment?

  29. Configuring Wildcards If you want to advertise a partial octet (subnet), you need to use wildcards. • 0.0.0.0 means all octets match exactly • 0.0.0.255 means that the first three match exactly, but the last octet can be any value After that, you must remember your block sizes….

  30. Wildcard The wildcard address is always one less than the block size…. • 192.168.10.8/30 = 0.0.0.3 • 192.168.10.48/28 = 0.0.0.15 • 192.168.10.96/27 = 0.0.0.31 • 192.168.10.128/26 = 0.0.0.63

  31. Wildcard Configuration of the Lab_B Router • Lab_A • E0: 192.168.30.1/24 • S0: 172.16.10.5/30 • Lab_C • E0: 192.168.50.1/24 • S1: 172.16.10.9/30 • Lab_B • E0: 192.168.40.1/24 • S0: 192.168.10.10/30 • S1: 192.168.10.6/30

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