11

CCNA3 – module 3 EIGRPCCNA3 – module 3 EIGRP

22

EIGRPEIGRP Cisco proprietary, released in 1994Cisco proprietary, released in 1994 Based on IGRPBased on IGRP EIGRP is an EIGRP is an advanced distance-vectoradvanced distance-vector

routing protocol that relies on features routing protocol that relies on features commonly associated with link-state commonly associated with link-state protocols. (sometimes called a protocols. (sometimes called a hybrid hybrid routing protocolrouting protocol))

Supports VLSM and CIDRSupports VLSM and CIDR Allows for multiple routed protocolsAllows for multiple routed protocols

33

EIGRPEIGRP Uses Hello protocols to create and maintain neighbor Uses Hello protocols to create and maintain neighbor

relationships and to determine when a link is down. relationships and to determine when a link is down. (Like link-state)(Like link-state) Every 5 seconds, with a hold timer of 15 secondsEvery 5 seconds, with a hold timer of 15 seconds Links less than T1 speed, Hellos are every 60 Links less than T1 speed, Hellos are every 60

seconds, hold timer of 180 secondsseconds, hold timer of 180 seconds Partial routing updates in response to topology Partial routing updates in response to topology

changeschanges When a change in topology occurs, EIGRP does not When a change in topology occurs, EIGRP does not

flood updates like link-state protocols, but flood updates like link-state protocols, but immediatelyimmediately sends those changes to its neighbors.sends those changes to its neighbors.

Has speed and efficiency of routing updates like a Has speed and efficiency of routing updates like a link-state protocol, along with a topology database.link-state protocol, along with a topology database.

44

EIGRP BenefitsEIGRP Benefits

Rapid Convergence – DUAL routing algorithm

Efficient use of bandwidth

partial, bounded updates – only sent to routers that need the information & not entire routing table

small “Hello” packets to keep in touch with other routers – minimal use of bandwidth

Supports VLSM and CIDR

Multiple network-layer support (multiprotocol)

IP, IPX, and AppleTalk

55

EIGRP and IGRPEIGRP and IGRP

AutomaticallyAutomatically redistributes when using same AS redistributes when using same AS number.number.

Topology example….Topology example….

RTC

RTB

RTA

RTD

192.168.1.0/24

10.1.1.0/24

172.16.1.0/24

IGRP 2446EIGRP 2446

66

Metric calculation: IGRP/EIGRPMetric calculation: IGRP/EIGRP

(with the following default constant values):(with the following default constant values):

Constant ValueConstant Value

K1K1 1 1

K2K2 0 0

K3 1K3 1

K4K4 0 0

K5K5 0 0

Notes Notes k2k2 metric effects metric effects LOADLOAD k4k4 and and k5k5 effects effects RELIABILITYRELIABILITY

metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)]

77

Metric CalculationMetric Calculation

Simplify the previous equation by Simplify the previous equation by applying the default constants…applying the default constants…

88

The metrics used by EIGRP in making routing The metrics used by EIGRP in making routing decisions are (decisions are (lower the metric the betterlower the metric the better):):

bandwidthbandwidth delaydelay loadload reliabilityreliability

By default, EIGRP uses only:By default, EIGRP uses only: Bandwidth (carrying capacity)Bandwidth (carrying capacity) Delay (end-to-end travel time)Delay (end-to-end travel time)

Metric CalculationMetric Calculation

99

If these are the default:If these are the default: bandwidth (default)bandwidth (default) delay (default)delay (default)

When are these used?When are these used? loadload reliabilityreliability

Use Use show interfaceshow interface command to view the command to view the metrics used on a specific interface that is metrics used on a specific interface that is routing EIGRP. routing EIGRP.

Metric CalculationMetric Calculation

1010

Metric Calculation – show interfacesMetric Calculation – show interfaces

Router> show interfaces s1/0

Serial1/0 is up, line protocol is up

Hardware is QUICC Serial

Description: Out to VERIO

Internet address is 207.21.113.186/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

rely 255/255, load 246/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

<output omitted>

1111

BandwidthBandwidth Expressed in Expressed in kilobitskilobits ( (show interfaceshow interface)) This is a This is a static numberstatic number and used for metric and used for metric

calculations only.calculations only. Does not necessarily reflect the actual bandwidth of Does not necessarily reflect the actual bandwidth of

the link.the link. You can adjust the bandwidth metric on an interface You can adjust the bandwidth metric on an interface

using what command?using what command? What command restores the interface bandwidth to What command restores the interface bandwidth to

the original default?the original default?

The default values:The default values: What is the default bandwidth of serial interfaces on What is the default bandwidth of serial interfaces on

CISCO routers?CISCO routers?

Metric Calculation – BandwidthMetric Calculation – Bandwidth

1212

DelayDelay Like bandwidth, delay it is a Like bandwidth, delay it is a static numberstatic number.. Expressed in Expressed in microsecondsmicroseconds, , millionths of a millionths of a

secondsecond (Uses the Greek letter mu with an S, (Uses the Greek letter mu with an S, S, NOT “ms” S, NOT “ms”

which is millisecond or which is millisecond or thousandths of a secondthousandths of a second))

The default values:The default values: What is the default delay of a Cisco serial What is the default delay of a Cisco serial

interface?interface?

IGRP/EIGRP metric uses the IGRP/EIGRP metric uses the sum of all of the sum of all of the delaysdelays of all of the outbound interfaces to the of all of the outbound interfaces to the destination network.destination network.

Metric Calculation – DelayMetric Calculation – Delay

1313

Changing the delay informational parameter:Changing the delay informational parameter:The delay can be changed using:The delay can be changed using: Router(config-if)# Router(config-if)# delaydelay tens-of- tens-of-SS (microseconds)(microseconds) Example of changing the delay on a serial interface to Example of changing the delay on a serial interface to

30,000 microseconds30,000 microseconds:: Router(config-if)# Router(config-if)# delaydelay 3000 3000

To restore the 20,000 microsecond default value: To restore the 20,000 microsecond default value: Router(config-if)# Router(config-if)# no delayno delay

Metric Calculation – DelayMetric Calculation – Delay

1414

IGRP vs EIGRP Metric CalculationIGRP vs EIGRP Metric Calculation

The differenceThe difference:: IGRP metric is 24 bits longIGRP metric is 24 bits long EIGRP metric is 32 bits longEIGRP metric is 32 bits long EIGRP metric is 256 times greater for the EIGRP metric is 256 times greater for the

same routesame route EIGRP allows for finer comparison of EIGRP allows for finer comparison of

potential routespotential routes

1515

IGRP vs EIGRP Metric CalculationIGRP vs EIGRP Metric Calculation

IGRPIGRP bandwidth = (10,000,000 ÷ bandwidth = (10,000,000 ÷ bandwidthbandwidth)) delay = delay = delay ÷ delay ÷ 1010

EIGRPEIGRP bandwidth = (10,000,000 ÷ bandwidth = (10,000,000 ÷ bandwidthbandwidth) * 256) * 256 delay = (delay = (delay ÷ delay ÷ 10) * 256 10) * 256

Note: The reference-bandwidth Note: The reference-bandwidth

For both IGRP and EIGRP: 10For both IGRP and EIGRP: 1077, , (10,000,000/bandwidth), whereas(10,000,000/bandwidth), whereas with OSPF it with OSPF it was 10was 108 8 (100,000,000/bandwidth)(100,000,000/bandwidth)

1616

Metrics – HOP COUNTMetrics – HOP COUNT

EIGRP also imposes a maximum hop count EIGRP also imposes a maximum hop count of 224of 224

IGRP maximum hop count of 255IGRP maximum hop count of 255 RIP maximum hop count of 15RIP maximum hop count of 15

1717

EIGRP ConfigurationEIGRP Configuration

RTA(config)# RTA(config)# router eigrp router eigrp ASAS

RTA(config-router)# network network

RTA(config-router)# eigrp log-neighbor-changes

RTA(config-if)#bandwidth kilobits

AS must be the same on all routers in the AS

If AS’s are identical on a router running both IGRP and EIGRP, routing tables are redistributed automatically.

Enables logging of neighbor adjacency changes to monitor stability & help detect problems

CISCO recommends this command.

EIGRP assumes default if not set.

If the link is slower, router might not converge, routing updates may be lost, or suboptimal path selection may result.

1818

EIGRP tablesEIGRP tables

Neighbor Topology Routing

1919

EIGRP Neighbor tablesEIGRP Neighbor tables

Lists adjacent routers One table for each routed protocol that

EIGRP supports

RTX#show ip eigrp neighborsIP-EIGRP neighbors for process 1

H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) Cnt Num

1 10.2.0.2 Se1 12 00:27:39 333 1998 0 10

0 10.1.0.1 Se0 14 01:17:14 40 240 0 27

2020

EIGRP Neighbor tablesEIGRP Neighbor tables

Fields in neighbor table: Neighbor address (Address) Hold time (Hold Uptime) Smooth round-trip timer (SRTT) Queue count (Q Cnt) Sequence number (Seq No)

2121

DUAL – calculating best pathsDUAL – calculating best paths

When the hold time expires, DUAL is informed of the topology change and must recalculate the new topology.

DUAL (Diffusing Update Algorithm) – allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change (distance-vector algorithm)

2222

EIGRP Topology tablesEIGRP Topology tables

Contains all of the EIGRP routing tables in the autonomous system DUAL combines information supplied by

neighbor and topology tables and calculates the lowest cost routes to each destination.

EIGRP routers track changes and switch to alternate routes when necessary

DUAL places this primary route, or successor route, information in the routing table

2323

EIGRP Topology tablesEIGRP Topology tablesTopology tables includes: Feasible distance (FD) – lowest calculated metric to

each destination. Route source (via xxx.xxx.xxx.xxx) – ID of router that

originally advertised route Reported distance (RD) – distance that an adjacent

neighbor reports to specific destination Interface information – interface through which the

destination is reachable Route status –

passive (P) – route is stable and ready for use Active (A) – route is in the process of being recomputed by

DUAL

2424

EIGRP Topology tablesEIGRP Topology tables

RTX#show ip eigrp topologyIP-EIGRP Topology Table for process 100

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status

P 200.10.3.0/24, 1 successors, FD is 2169856

via Connected, Serial1

via Redistributed (2169856/0)

P 200.10.4.0/24, 1 successors, FD is 2169856

via Connected, Serial0

RD

2525

EIGRP Topology tablesEIGRP Topology tables

Successor – route that is selected as the primary route to use to reach a destination.

DUAL identifies and places route in routing table There can be up to four successor routes for any

particular route. Copy of successor is also placed in topology table

EIGRP sorts the topology table so that the successor routes are at the top, followed by the feasible successors. Bottom of list may include routes that DUAL believes to be loops.

2626

EIGRP Topology tablesEIGRP Topology tables

Feasible Successor – backup route Identified at same time as successor but kept only

in the topology table May have multiple feasible successors but not

mandatory to have any They are neighbors that are downstream (closer

to the destination) Must have lower advertised cost (RD) than

existing successor’s FD If feasible successor not identified, active status

placed on route and query packets sent to all neighbors to recompute topology.

2727

Successor & Feasible SuccessorSuccessor & Feasible Successor

2828

Recomputation of RoutesRecomputation of RoutesIf route becomes unavailable and DUAL cannot find feasible successor.

Neighbor routers are compelled to answer query for a loop-free path.

If neighbor has no route, it responds so.

Excess computation = network instability

To prevent convergence problems, DUAL always tries to find a feasible successor before resorting to recomputation

2929

Recomputation of RoutesRecomputation of RoutesStuck in Active routers –

one or more routers don’t respond to query (180 seconds) then routes placed in stuck in active state

EIGRP then clears its table of neighbors that did not respond

3030

Route TaggingRoute TaggingRouting Table –

Internal routes

routes originating within the EIGRP AS

External routes

routes originating outside the EIGRP AS

3131

Routing Table & TaggingRouting Table & TaggingRouterB#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B – BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1, E2 - OSPF external type 2, E – EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route

Gateway of last resort is not set

C 10.1.1.0 is directly connected, Serial0

D 172.16.0.0 [90/2681856] via 10.1.1.0, Serial0

D EX 192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0

External EIGRP routes are redistributed from IGRP networks

3232

RTA#show ip route<output omitted>C 10.1.1.0 is directly connected, Serial0D 172.16.0.0 [90/2681856] via 10.1.1.0, Serial0D EX 192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0

External EIGRP routes are redistributed from IGRP networks

RTC#show ip route<output omitted>C 192.168.1.0 is directly connected, Serial0I 10.1.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0I 172.16.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0

RTC only sees IGRP routes

192.168.1.0 was redistributedfrom IGRP

RTC

RTB

RTA

RTD

192.168.1.0/24

10.1.1.0/24

172.16.1.0/24

IGRP 2446EIGRP 2446

3333

Hellos & RTPHellos & RTPHello Packets

Sent every 5 seconds (high-bandwidth links) and every 60 seconds by default (low-bandwidth links)As long as routers receive hello packets – route in passive state

Reliable Transport Protocol (RTP)Layer 4 protocolGuarantees delivery of packetsAllows EIGRP to multicast and unicast to different peers simultaneously

3434

DUAL FSMDUAL FSMDUAL Finite-State Machine (DUAL FSM)

Full name of DUAL technologyTracks routes advertised by neighbors and uses composite metric to compare themGuarantees each path is loop-freeInserts lowest-cost paths (successor routes) into routing tableNeighbor & Topology tables supply DUAL with route information to make decisions quickly

3535

DUAL FSMDUAL FSM

FD is not mandatory

2 < 3

3636

EIGRP PacketsEIGRP Packets

•Hello Packets

•5 second updates (T1/Point-to-Point link)

•Multicast on IP address 224.0.0.10

•Hold Time = 3 times the Hello interval

(15 seconds)

•Neighbor routers hello and dead intervals do not need to match with EIGRP (unlike OSPF)

3737

EIGRP PacketsEIGRP Packets

•Acknowledgement•Used by RTP to signal reliable exchange of information

•Hello packet without data; unicast to specific host

•Update•Discovery of new neighbor

•EIGRP router sends unicast to neighbor so that it can add to its topology table

•EIGRP router send multicast to all neighbors if topology change occurs

3838

EIGRP PacketsEIGRP Packets

•Query & Reply•Query - Used to obtain specific information from one or all of its neighbors (multicast or unicast)

•Reply – response to query (unicast)

•Used, for example, if DUAL places a route in active state and multicasts neighbors, searching for successor

3939

EIGRP Route SummarizationEIGRP Route SummarizationEIGRP automatically summarizes routes at the classful boundary

This may not be preferable, especially if using VLSM

To disable auto-summarization:

Router(config-router)#no auto-summary

Manual Summarization command:

Router(config-if)#ip summary-address eigrp AS ip-address subnet-mask administrative distance(configured on a per-interface basis)

4040

EIGRP Route SummarizationEIGRP Route Summarization

4141

Verifying EIGRPVerifying EIGRP

Show ip eigrp neighbors Show ip eigrp interfaces Show ip eigrp topology Show ip eigrp topology all-links Show ip eigrp traffic AS Debug eigrp fsm Debug eigrp packets

4242

RIP, IGRP, & OSPF RIP, IGRP, & OSPF TroubleshootingTroubleshooting

Show & debug commandsShow & debug commands Debug ip rip Debug ip igrp events Debug ip igrp transactions Debug ip ospf events Show ip route Show running-config Show ip protocols show ip ospf neighbor