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CCNA 3 v3.1 Module 3

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CCNA 3 Module 3

Enhanced Interior Gateway Routing Protocol (EIGRP)

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EIGRP• Cisco-proprietary routing protocol

Based on Interior Gateway Routing Protocol (IGRP)

• How does EIGRP improve on IGRP

Supports classless interdomain routing (CIDR)

Network designers can maximize address space

Variable-length subnet mask (VLSM)

Fast convergence times

Improved scalability

Superior handling of routing loops.

• Hybrid routing protocol combining

distance vector and link-state algorithms

• An ideal choice for large, multi-protocol networks built primarily on Cisco routers

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EIGRP Versus IGRP

• Compatibility modeIGRP and EIGRP are interoperable

EIGRP offers multiprotocol support

• Metric calculation (Bandwidth + Delay)EIGRP - 32 bit metric for bandwidth and delay

IGRP – 24 bit metric for bandwidth and delay

IGRP Bandwidth = 1000000/bandwidth Kbps

EIGRP Bandwidth = (1000000/bandwidth Kbps)*256

IGRP Delay = delay/10

EIGRP Delay = (delay / 10) * 256

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• Hop count

IGRP maximum hop is 255

EIGRP maximum hop is 224

• Automatic protocol redistribution

IGRP and EIGRP can share routes if both have the same autonomous system number

• Route tagging

EIGRP tags routes learned from IGRP as external

IGRP does not tag routes

• Holddown timers

EIGRP 180

IGRP 280

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D = EIGRP routingEX = External routeI = IGRP routing

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EIGRP Terminology and Concepts

• Holds route and topology information in RAM

• EIGRP Tables

Neighbor Table

Topology Table

Routing Table

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Neighbor Table• Lists adjacent routers

• Similar to OSPFs adjacency database

• One for each protocol EIGRP supports

• Neighbors send hello packets

Containing holddown timer

If neighbor does not send another hello packet before holddown timer expires the neighbor is unreachable or unoperational

When the hold time expires

Diffusing Update Algorithm (DUAL) (EIGRP distance vector algorithm) recalculate the new topology

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NB

• Fields in the neighbor table

Neighbor Address

Layer 3 address of neighbor router

Hold time

Time to wait before considering link down

Smooth Round Trip timer

Average time to send and receive packet

Queue count

Amount of IEGRP packets in queue

Sequence number

Number of last packet received from neighbor

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Topology Table

• All EIGRP routing tables in the AS

• DUAL takes information from neighbor table and topology table and calculates the lowest cost routes to each destination

• Successor

Neighbor router that is the next hop in a least cost, loop-free path to a destination

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

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Admin distance

Feasible Distance (e.g., 90) - the lowest metric (cost) to each destination

Route Source (via 200.10.10.10) – router that originally advertised that route

Reported Distance (e.g., 2195456) – cost of route as advertised by the neighbor router

Interface information – The interface through which the destination is reachable

Route status – passive (P) the route is stable and ready for use

active (A) the route is in the process of being recomputed by DUAL

FD/RD

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EIGRP Routing Table

• Holds the best routes to a destination

• Routing table for each network protocol.

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

The preferred root to the destination

DUAL calculates this using neighbor and topology tables

It is placed in the routing table

A copy if it is placed in the topology table

Up to 4 successor routes for any particular route

equal or unequal cost

identified as the best loop-free paths to a given destination

• A feasible successor (FS) is a backup route

only kept in the topology table

not mandatory

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EIGRP Design Features

• Rapid convergence

DUAL guarantees loop-free operation at every instant throughout a route computation allowing all routers involved in a topology change to synchronize at the same time

• Efficient use of bandwidth

partial, incremental updates to routers that need the information (bounded updates)

Hello packets keep routers in touch with each other

• Support for variable-length subnet mask (VLSM) and classless interdomain routing (CIDR)

• Multiple network-layer support

supports IP, IPX, and AppleTalk through protocol-dependent modules (PDMs).

• Independence from routed protocols.

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EIGRP Technologies1. Neighbor discovery and recovery

Form adjacencies by sending Hello packet every five seconds

This allows EIGRP to

Dynamically learn of new routes that join their network

Identify routers that become either unreachable or inoperable

Rediscover routers that had previously been unreachable

2. Reliable Transport Protocol (RTP)

Transport-layer protocol guarantee ordered delivery of EIGRP packets to all neighbors – used for reliability of transmission

3. DUAL finite-state machine algorithm

Contains all the logic used to calculate and compare routes in an EIGRP network

DUAL tracks all the routes advertised by neighbors

DUAL also guarantees that each path is loop free

DUAL inserts lowest cost paths into the routing table (successor routes)

DUAL places a copy of successor routes in the topology table(feasability successor)

4. Protocol-dependent modules

Support for routed protocols, such as IP, IPX, and AppleTalk

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EIGRP Data Strucutre

• EIGRP Packet TypesHello - discover, verify, rediscover neighbor routers

Sent unreliably – no acknowledgement needed

EIGRP routers send hellos to the multicast IP address 224.0.0.10

Default hello interval depends on the bandwidth of the interface

Acknowledgment - indicate receipt of any EIGRP packet during a reliable exchange

Update - unicast update packets sent to new neighbor so that it can add to its topology table

Query – to find specific information about a router

Reply – response to a query

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EIGRP Configuration

• router(config)#router eigrp autonomous-system-number

AS-number identifies all routers within the internetwork

• router(config-router)#network network-number

Specify all connected networks only

• router(config-if)#bandwidth kilobits

Set the bandwidth for the serial link

• router(config-if)#eigrp log-neighbor-changes

enables the logging of neighbor adjacency changes to monitor the stability of the routing system and to help detect problems

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• Why is it necessary to set the bandwidth

n/w may be unable to converge if bandwidth setting does not match actual bandwidth

A suboptimal route may be chosen as the best path to a destination if the bandwidth setting is higher than the actual bandwidth

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Configuring EIGRP summarization • EIGRP automatically summarizes routes at the classful

boundary

summarization keeps routing tables as compact as possible

• router(config-router)#no auto-summary Turns off route summarization when manually configuring

• To manually configure a summary address

router(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance

• Administrative distance for EIGRP summary routes

Default is 5

Can be configured to between 1 and 255

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• It is necessary to configure the bandwidth setting on an EIGRP interface rather than leaving it at the default setting because

A suboptimal route may be chosen as the best path to a destination if the bandwidth setting is higher than the actual bandwidth of the link

The network may be unable to converge if the bandwidth setting does not match the actual bandwidth of the link.

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Verifying EIGRP• Show ip eigrp neighbors

Displays eigrp neighbor table

• Show ip eigrp interfaces

Displys eigrp information for each interface

• Show ip eigrp topology [keyword]

Displays feasible successors

Keywords - Active, pending, zero successor

• Show ip eigrp all-links

Displays all routes not just feasable successors

• Show ip eigrp traffic

Displays the number of eigrp packets sent/recieved

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Troubleshooting RIP

• RIP Problems

Most common problem RIP V1prevent variable-length subnet mask (VLSM) being advertised.

Layer 1 or Layer 2 connectivity issues exist.

Mismatched RIP v1 and RIP v2 routing configurations exist.

Network statements are missing or incorrectly assigned.

The outgoing interface is down.

The advertised network interface is down.

• Troubleshooting

show ip protocols displays current state of the active routing protocol process

debug ip rip Display information on RIP routing transactions

Turn this off using no debug ip rip, no debug all, or undebug all

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Troubleshooting IGRP

• IGRP Problem checks

Layer 1 or Layer 2 connectivity issues exist.

Autonomous system numbers on IGRP routers are mismatched.

Network statements are missing or incorrectly assigned.

The outgoing interface is down.

The advertised network interface is down.

• To debug IGRP

debug ip igrp transactions [host ip address]

to view IGRP transaction information

debug ip igrp events [host ip address]

to view routing update information

To turn off debugging, use the no debug ip igrp command.

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Troubleshooting EIGRP

• Possible reasons why EIGRP is not working correctly

Layer 1 or Layer 2 connectivity issues exist

most common reasons for a missing neighbor is failure on the actual link

Autonomous system numbers on EIGRP routers are mismatched.

The link may be congested or down.

The outgoing interface is down.

The advertised network interface is down.

Auto-summarization is enabled on routers with discontiguous subnets.

Use no auto-summary to disable automatic network summarization

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• Show ip route eigrp

Displays current eigrp entries in routing table

• Show ip protocols

Displays EIGRP AS number, filtering and redistribution numbers, neighbors

• Show ip eigrp traffic

Displays packets sent and recieved

Static on hello, update, query, replies, acks

• Eigrp log-neighbor-changes

Displays a history of when and why neighbors have been reset

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Troubleshooting OSPF

• Show ip ospf neighbor

Displays OSPF neighbor one each interface

Displays routes known to the router and how they were learned

• Show ip ospf interface

Displays timer intervals, neighbor adjacencies

Determines if OSPF is enabled on each interface

• Debug ip ospf events

Displays Adjacencies, Flooding information, Designated router selection, Shortest path first (SPF) calculation

• Debug ip ospf packets

Displays information about OSPF packets received

• No debug ip ospf packets

Turns off debugging

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