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CCNA 3 v3.1 Module 3 EIGRP

Claes Larsen, CCAI

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Objectives

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Comparing EIGRP with IGRP

• Comparisons between EIGRP and IGRP fall into the following major categories:

Compatibility mode

Metric calculation

Hop count

Automatic protocol redistribution

Route tagging

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Using EIGRP with IGRP

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EIGRP and IGRP Metric Calculation

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Comparing show ip route for EIGRP and IGRP

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EIGRP Concepts

• The following three tables are maintained by EIGRP:

Neighbor table

Topology table

Routing table

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The EIGRP Topology Table

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EIGRP Concepts

• Every EIGRP router maintains a topology table for each configured network protocol.

• All learned routes to a destination are maintained in the topology table.

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EIGRP Design Features

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EIGRP Technologies

• Neighbor discovery and recovery

• Reliable Transport Protocol

• DUAL finite-state machine algorithm

• Protocol-dependent modules

• By forming adjacencies, EIGRP routers:

Dynamically learn of new routes that join their network

Identify routers that become either unreachable or inoperable

Rediscover routers that had previously been unreachable

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Data Structure

The five EIGRP packet types are as follows:

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Default Hello Intervals and Hold Times for EIGRP

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EIGRP Successors and Feasible Successors

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• Successor – Current Route

A successor is a route selected as the primary route to use to reach a destination.

Successors are the entries kept in the routing table.

• Feasible Successor - A backup route

A feasible successor is a backup route.

These routes are selected at the same time the successors are identified, but they are kept in the topology table.

Multiple feasible successors for a destination can be retained in the topology table.

Let’s see how this works!

EIGRP Terminology and Operations

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Successors and Feasible SuccessorsFeasible distance (FD) is the minimum distance (metric) along a path to a destination network.

Reported distance (RD) is the distance (metric) towards a destination as advertised by an upstream neighbor. Reported distance is the distance reported in the queries, the replies and the updates.

A neighbor meets the feasible condition(FC) if the reported distance by the neighbor is smaller than or equal to the current feasible distance (FD) of this router. "If a neighbors metric is less than mine, then I know the neighbor doesn't have a loop going through me."

A feasible successor is a neighbor whose reported distance (RD) is less than the current feasible distance (FD). Feasible successor is one who meets the feasible condition (FC).

Your route (metric) to the network (RD to me) must be LESS than my current route (my total metric) to that same network. If your route (metric) to the network (RD to me) is LESS than my current route (my total metric), I will include you as a FEASIBLE SUCCESSOR.

If your route (metric) to the network (RD to me) is MORE than my current route (my total metric), I will NOT include you as a FEASIBLE SUCCESSOR.

Successors and Feasible Successors

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Successors og Feasible Successors

RTA kan nå netværk 24 på tre forskellige måder. Via RTX, RTY og RTZ

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Successors og Feasible Successors

Advertised or Destination Feasible Dist. Reported. Dist. Nabo

Netværk 24 40 30 RTX I Topolog Tabel

Netværk 24 31 21 RTY I Routing Tabel

Netværk 24 230 220 RTZ Ikke i Topologi Tabel

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Successors og Feasible Successors

• RTY er successor med en computed cost på 31.• “31” er Feasible Distance (FD).

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Successors og Feasible Successors

• RTX er feasible successor fordi dens RD er mindre end eller lig med FD.- RTX’s RD (30) er mindre end RTA’s FD (31) via RTY.

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Successors og Feasible Successors

Der er tre trin når der vælges

Feasible successor:

• Bestem hvilken nabo der har en RD til net værket der er mindre end FD.

• Bestem den vej der har den mindste cost værdi på nær den der er valgt som successor.

• Vælg den vej som opfylder begge kriterier.

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Successors og Feasible Successors

• RTZ er ikke Feasible Successor, da RD220 ikke< FD31

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DUAL example

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DUAL example

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DUAL example

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DUAL example

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DUAL example

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DUAL example

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Configuring EIGRP

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EIGRP Automatically Summarizes Based on Class

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Manual Summarization with EIGRP

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Verifying EIGRP

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EIGRP debug Commands

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Building Neighbor Tables

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Discover Routes

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Select Routes

• If a link goes down, DUAL looks for an alternative route path, or feasible successor, in the topology table.

• If a feasible successor is not found, the route is flagged as Active, or unusable at present.

• Query packets are sent to neighboring routers requesting topology information.

• DUAL uses this information to recalculate successor and feasible successor routes to the destination.

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Troubleshooting Process

1. Analyze the network failure, make a clear problem statement.

2. Gather the facts needed to help isolate possible causes.

3. Consider possible problems based on the facts that have been gathered.

4. Create an action plan based on the remaining potential problems.

5. Implement the action plan, performing each step carefully while testing to see whether the symptom disappears.

6. Analyze the results to determine whether the problem has been resolved. If it has, the process is complete.

7. If the problem has not been resolved, create an action plan based on the next most likely problem in the list. Return to Step 4, change one variable at a time, and repeat the process until the problem is solved.

8. Once the actual cause of the problem is identified, try to solve it.

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Use show Commands and TCP/IP Tools

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Troubleshooting RIP Configuration

• Layer 1 or Layer 2 connectivity issues exist.

• VLSM subnetting is configured. VLSM subnetting cannot be used with RIPv1

• Mismatched RIPv1 and RIPv2 routing configurations exist.

• Network statements are missing or incorrectly assigned.

• The outgoing interface is down.

• The advertised network interface is down.

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Troubleshooting IGRP Configuration

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Troubleshooting EIGRP Configuration

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Troubleshooting EIGRP Configuration

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Troubleshooting OSPF Configuration

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Summary