05.EIGRP Fundamentals

7/28/2019 05.EIGRP Fundamentals

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Cisco CCNP ROUTE TrainingInstructor: Joe Rinehart, CCIE #14256

EIGRP Fundamentals

Cisco CCNP ROUTE Training

EIGRP Fundamentals

In This Lesson:

EIGRP Protocol Mechanics

Tables Used by EIGRP

EIGRP Metric Calculations

Configuration of Basic EIGRP Lab Exercises

Verification of EIGRP Process/Operation


EIGRP Fundamentals


1. EIGRP Neighbor Relationships

2. Packet Types

3. Topology Exchange Process


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EIGRP Fundamentals


EIGRP Neighbor Relationships

EIGRP Establishes Formal NeighborRelationships

Must be directly connected

Peering must be on primary subnets

K-Values must match

AS numbers must match

Authentication strings must match

EIGRP Uses Hello Messages for NeighborDiscovery and Maintenance

Multicast to 224.0.0.10

Single peering relationship betweenall routers on multi-access networks


EIGRP Fundamentals


EIGRP Neighbor Relationships

EIGRP Uses Hello Messages for NeighborDiscovery and Maintenance

Sent at regular intervals on all

configured interfaces

Every 5 seconds (high speedinterfaces)

Every 60 seconds (low speedinterfaces)

Hold-Time = amount of time isconsidered alive (3x hello interval)

15 seconds (high speed)

180 seconds (low speed)


EIGRP Fundamentals


Packet Types

All packets use IP protocol 88 (notTCP/UDP)

Reliable Transport Protocol used to

transmit data to neighbors usingmulticast or unicast

EIGRP Packet Types:

Hello

Update

Query

ACK

Goodbye

Function(s) Sent

Reliably?

ACK

Req?

Multicast

orUnicast

Hello Neighbor

discovery and

maintenance

N N M

Update Routing

information

Y Y Both

Query Request for

neighbor to

verify route

to a subnet

Y Y Both

Reply Reply to

query

Y Y U

ACK Acknowledge

s query,

update and

response

packets

N N U

Goodbye Graceful

shutdown

N N U


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EIGRP Fundamentals


Topology Table

List of EIGRP routes either local or fromupdates (show ip eigrp topology)

P: Passive, network available andusable in routing table

A: Active, network not available, in

current calculation process

U: Update, network is being updated

Q: Query, network query request hasbeen sent/awaiting response

R: Reply, router sendingreply/awaiting ACK

s: SIA status, query notacknowledged/convergence problem


EIGRP Fundamentals


IP Routing Table

List of EIGRP routes installed and usablefor routing (show ip route eigrp)

D: EIGRP internal route (AD of 90)

EX: EIGRP external route(redistributed, AS of 170)

192.168.44.0/24: Destinationprefix/bits

90/10639872: Administrativedistance of the route/feasible distanceof the route

via: Source of the routingupdate/next-hop address


EIGRP Fundamentals


1. EIGRP Metric Weights/K-Values

2. Metric Calculation Process

3. EIGRP Route Selection/DUAL Methodology


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EIGRP Fundamentals


EIGRP Metric Weights/K-Values

EIGRP Uses Multiple Data Points forMetric Calculation, termed K Values:

K1: Bandwidth (smallest along path)

K2: Load (1-255)

K3: Delay (cumulative, in tens ofmicroseconds)

K4: Reliability (1-255)

K5: MTU (minimum, never used)

EIGRP Only Uses Bandwidth and Delay inroute calculation (K1=1, K2=0, K3=1,

K4=0, K5=0)

Changed using metric weights

FastEthernet0/0.13 is up, line protocol

is up

Hardware is AmdFE, address is0004.9a90.f6a0 (bia 0004.9a90.f6a0)

Internet address is 192.168.13.1/26

MTU 1500 bytes, BW 100000 Kbit,

DLY 100 usec, reliability 255/255,

txload1/255, rxload1/255

Encapsulation ISL Virtual LAN, Color

13.

ARP type: ARPA, ARP Timeout

04:00:00

Last clearing of "show interface"

counters never


EIGRP Fundamentals


Metric Calculation Process

Values used in metric calculation maylook large and confusing

EIGRP metrics are always expressed in

integer format (no decimals)

EIGRP metric to 10.3.3.3 (R3 Loopback)is calculated using Fa0/0 (100 Mbps) path

Using an Excel-based calculator, themetric from R1 to R3 for network10.3.3.3/32 results in a value of 156160

Metric values are displayed in the EIGRP

topology and IP routing tables

Additional path exists on s0/0.134

EIGRP METRIC CALCULATOR

IN PUTS R ESULT100,000 Least-BW

156160 EIGRP METRIC510 Delay

METRIC = (( 10^7 / Least-BW ) + Cumulative Delay ) * 256


EIGRP Fundamentals


EIGRP Route Selection/DUAL

Methodology EIGRP calculates two values to use when

selecting the best route to a subnet:

Feasible Distance (FD): Metric ofthe best route to a subnet ascalculated locally on a router

Reported Distance (AD): Metric ofthe best route to a subnet as

calculated/reported by an EIGRPneighbor

FD to reach 10.3.3.3/32 from R1 is156160 (RD + cost to R3)

RD for 10.3.3.3/32 from R3 is 128256


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EIGRP Fundamentals


EIGRP Route Selection/DUALMethodology

EIGRP uses a mathematical calculation

called the Feasible Condition to determineif a route is loop-free and thus usable:

IF AD < RD of Route Then

Feasible Condition is TRUE

Routes chosen by DUAL are referred toas:

Successor: Best route to a subnetand installed in the routing table

Feasible Successor: Route meetingthe Feasible Condition, immediatelyusable upon failure of the Successor

Prefix 10.3.3.3/32

Successor FS

192.168.13.3 172.16.134.3

FD 1 56 ,1 60 1 0, 63 9, 87 2

AD 128,256 128,256

BW 100,000 256

Delay 5,100 25,000


EIGRP Fundamentals


EIGRP Route Selection/DUALMethodology

When a route (successor) fails and nofeasible successor exists, EIGRP uses

DUAL to calculate a new route:

Query is sent regarding the route toall directly connected neighbors

If neighbor failed also, neighbor isdeleted from the neighbor table

While route to the subnet is beingqueried/calculated, it is referred to as

going active

When the new successor is selectedthe route returns to passive status

Prefix 10.3.3.3/32

Successor FS

192.168.13.3 172.16.134.3

FD 1 56 ,1 60 1 0, 63 9, 87 2

AD 128,256 128,256

BW 100,000 256

Delay 5,100 25,000


EIGRP Fundamentals


1. Review of EIGRP Configuration Commands

2. Devices Involved in EIGRP Domain

3. Configuration of EIGRP Routers


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EIGRP Fundamentals


Review of EIGRP ConfigurationCommands

Creation of the EIGRP Routing Process

router eigrp

Autonomous System number mustmatch on all devices

Use no auto-summary to disableautomatic summarization

Topology table is seeded from twosources:

Networks/subnets on interfaces usingthe networksubcommand

Networks learned through theredistribute subcommand


EIGRP Fundamentals


Review of EIGRP ConfigurationCommands

Adjusting Bandwidth Specifications

LAN interfaces automatically calculate

correct bandwidth

Serial interfaces default to 1544 Kbps

Manual adjustment done usingbandwidth interfacesubcommands

Manually Configuring the Router-ID

EIGRP chooses the highest loopbackas the router id, or the highest IPaddress on a valid interface


EIGRP Fundamentals


Review of EIGRP Configuration

Commands Manually Configuring the Router-ID

Configured using ip eigrp router-id

command

Adjusting the Bandwidth Usage on anInterface

Default is 50% of the configuredbandwidth

Adjusted using the ip bandwidth-percent eigrp interfacesubcommand


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EIGRP Fundamentals


Devices Involved in EIGRP Domain

Router 1 (R1)

Multipoint and point-to-point frame-relay subinterfaces

Redundant link to R3 (VLAN 12)

Router 2 (R2)

Point-to-point frame-relaysubinterface

VLAN connection to R5

Router 3 (R3)

Router 4 (R4): Supplying default route

Router 5 (R5): Stub configuration

ASA 5505: Connection to Internet


EIGRP Fundamentals


Configuration of EIGRP Routers

Using AS 100 on all EIGRP Routers

Specifying Loopback 0 as Router-ID

Disabling Automatic NetworkSummarization

Manually Configuring Serial InterfaceBandwidth

R1 Multipoint: 256 Kbps

R1 Point-to-Point: 128 Kbps

R2/R3/R4 Interfaces: 128 Kbps

Limiting Serial Interface BandwidthConsumption of 45% by EIGRP


EIGRP Fundamentals


1. Verifying Basic EIGRP Configuration

2. Verifying Functional Neighbor Relationships

3. Correcting the Split-Horizon Issue


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EIGRP Fundamentals


Verifying Basic EIGRP Configuration

Confirming that EIGRP is Operational

Examine the output of the show ipprotocols command (see left)

Verify process is running

Verify networks/subnets

Confirming EIGRP is on Interfaces

Examine the output of the show ipeigrp interfaces command

Expected interfaces appear

Correct ASN is displayed

Peers are shown in interfacestatistics


EIGRP Fundamentals


Verifying Functional NeighborRelationships

Confirming that neighbors are peering

Examine the output of the show ip

eigrp neighbors command (see left)

Correct interface displayed

Correct IP address(es) displayed

Statistics are non-zero

Use ping and trace commands toconfirm connectivity is active

Confirm the presence of expectednetworks in IP routing table using theshow ip route eigrp command


EIGRP Fundamentals


Correcting the Split-Horizon Issue

Problem: Missing Networks in IP RoutingTable

R1: All networks included from both

R4 and R3

R3: All networks being advertisedfrom R4 not included

R4: All networks being advertisedfrom R4 not included

Solution: R1 is Using the Split-HorizonRule on its S0/0.134 multipointsubinterface, issue the no ip split-horizon eigrp 100 on the subinterface


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EIGRP Fundamentals

Key Terms You Should Know

RTP Reliable Transport Protocol, data transmission protocolused by EIGRP to ensure guaranteed, ordered delivery

K-Values Also referred to as metric weights, the

components used to calculate the EIGRP metric

Hold-Time Expressed as a multiplier of 3X the hello-interval, itdesignates how long to wait before declaring a neighbor dead

Feasible Distance EIGRP metric to a destination network

Reported Distance EIGRP metric to a destination network asreported by the next-hop router

Feasible Condition Test of a valid, loop-free route, when thereported distance is less than the feasible distance

Successor Valid primary EIGRP route to a destination network

Feasible Successor Valid secondary EIGRP route to adestination network, and usable immediately


EIGRP Fundamentals

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