Routing Protocols and Concepts

© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

Routing Protocols and Concepts

EIGRPChapter 9Modified by Pete Brierley

ITE PC v4.0Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

What will we Learn from chapter 9?

Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).

Examine the basic EIGRP configuration commands and identify their purposes.

Calculate the composite metric used by EIGRP.

Describe the concepts and operation of DUAL.

Describe the uses of additional configuration commands in EIGRP.


Introduction


Terms you MUST knowRIPng

Weights

Hold time

TLV

Neighbor Table

Routing Table

Topology Table

Bounded Updates

Summary routes

Quan zeros

AS

Wildcard mask

IPv6

K values

Reliability

Load

Delay

Bandwidth

Successor

Feasible Distance

RD

FC

Feasible Successor

FSM

Internal routes

External routes

OP Code

PDM

RTP

Unicast

Multicast

Hello packet

Adjacencies

DUAL

IANA

Null 0

Aperiodic


EIGRP Roots of EIGRP: IGRP

-Developed in 1985 to overcome RIPv1’s limited hop count-Distance vector routing protocol-Metrics used by IGRP

bandwidth (used by default)Delay (used by default)reliabilityload

-IGRP discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S


EIGRPEIGRP Message Format

EIGRP HeaderData link frame header - contains source and destination MAC addressIP packet header - contains source & destination IP addressEIGRP packet header - contains AS numberType/Length/Field - data portion of EIGRP message


EIGRP

EIGRP packet header contains

–Opcode field–Autonomous System number

EIGRP Parameters contains–Weights –Hold time


EIGRP

TLV: IP internal contains–Metric field–Subnet mask field–Destination field

TLV: IP external contains–Fields used when external routes are imported into EIGRP routing process


EIGRPProtocol Dependent

Modules (PDM) EIGRP uses PDM to route

several different protocols i.e. IP, IPX & AppleTalk

PDMs are responsible for the specific routing task for each network layer protocol


EIGRPReliable Transport Protocol (RTP) Purpose of RTP

–Used by EIGRP to transmit and receive EIGRP packets

Characteristics of RTP–Involves both reliable & unreliable delivery of EIGRP packet

Reliable delivery requires acknowledgment from destinationUnreliable delivery does not require an acknowledgement from destination

–Packets can be sent UnicastMulticast

–Using address 224.0.0.10


EIGRPEIGRP’s 5 Packet Types

Hello packets–Used to discover & form adjacencies with neighbors


EIGRP Update packets

–Used to propagate routing information

Acknowledgement packets

–Used to acknowledge receipt of update, query & reply packets


EIGRP Query & Reply packets

Used by DUAL for searching for networksQuery packets

-Can use UnicastMulticast

Reply packet -Use only

unicast


EIGRP Purpose of Hello Protocol

–To discover & establish adjacencies with neighbor routers

Characteristics of hello protocol–Time interval for sending hello packet

Most networks it is every 5 secondsMultipoint non broadcast multi-access networks

–Unicast every 60 seconds-Holdtime

This is the maximum time router should wait before declaring a neighbor downDefault holdtime

–3 times hello interval


EIGRPEIGRP Bounded Updates EIGRP only sends update when there is a change in

route status Partial update

–A partial update includes only the route information that has changed – the whole routing table is NOT sent

Bounded update–When a route changes, only those devices that are impacted will be notified of the change

EIGRP’s use of partial bounded updates minimizes use of bandwidth


EIGRP

Diffusing Update Algorithm (DUAL)–Purpose

•EIGRP’s primary method for preventing routing loops–Advantage of using DUAL

•Provides for fast convergence time by keeping a list of loop-free backup routes


EIGRP

Administrative Distance (AD)–Defined as the trustworthiness of the source route

EIGRP default administrative distances–Summary routes = 5–Internal routes = 90–Imported routes = 170


EIGRP

Authentication EIGRP can

– Encrypt routing information

– Authenticate routing information


EIGRPNetwork Topology Note the ISP router


EIGRP EIGRP will automatically

summarize routes at classful boundaries


EIGRP


Basic EIGRP Configuration Autonomous System (AS) & Process IDs

–This is a collection of networks under the control of a single authority (reference RFC 1930)–AS Numbers are assigned by IANA

–Entities needing AS numbersISPInternet Backbone prodiersInstitutions connecting to other institutions using AS numbers


Basic EIGRP Configuration EIGRP autonomous system

number actually functions as a process ID

Process ID represents an instance of the routing protocol running on a router

ExampleRouter(config)#router

eigrp autonomous-system


Basic EIGRP ConfigurationThe router eigrp command

The global command that enables eigrp isrouter eigrp autonomous-system -All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)


Basic EIGRP ConfigurationThe Network Command

Functions of the network command–Enables interfaces to transmit & receive EIGRP updates–Includes network or subnet in EIGRP updates

Example–Router(config-router)#network network-address


Basic EIGRP Configuration The network Command with a Wildcard Mask

-This option is used when you want to configure EIGRP to advertise specific subnets-Example Router(config-router)#network network-address [wildcard-mask]


Basic EIGRP ConfigurationVerifying EIGRP EIGRP routers must establish adjacencies with their neighbors before

any updates can be sent or received

Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is

show ip eigrp neighbors


EIGRP

The show ip protocols command is also used to verify that EIGRP is enabled


Basic EIGRP Configuration

Examining the Routing Table

The show ip route command is also used to verify EIGRP

EIGRP routes are denoted in a routing table by the letter “D”

By default , EIGRP automatically summarizes routes at major network boundary


Basic EIGRP Configuration Introducing the Null0 Summary Route

–Null0 is not a physical interface–In the routing table summary routes are sourced from Null0

Reason: routes are used for advertisement purposes–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met

At least one subnet is learned via EIGRPAutomatic summarization is enabled


Basic EIGRP Configuration R3’s routing table shows

that the 172.16.0.0/16 network is automatically summarized by R1 & R3


EIGRP Metric CalculationEIGRP Composite Metric & the K Values EIGRP uses the following values in its composite metric

-Bandwidth, delay, reliability, and load The composite metric used by EIGRP

– formula used has values K1 K5K1 & K3 = 1all other K values = 0


EIGRP Metric Calculation Use the sh ip protocols command to verify the K

values


EIGRP Metric CalculationEIGRP Metrics

Use the show interfaces command to view metrics

EIGRP MetricsBandwidth – EIGRP uses a static bandwidth to calculate metricMost serial interfaces use a default bandwidth value of 1.544Mbos (T1)


EIGRP Metric CalculationEIGRP Metrics

Delay is the defined as the measure of time it takes for a packet to traverse a route

-it is a static value based on link type to which interface is connected


EIGRP Metric Calculation Reliability (not a default EIGRP metric)

-A measure of the likelihood that a link will fail-Measure dynamically & expressed as a fraction of 255

the higher the fraction the better the reliability

Load (not a default EIGRP metric)– A number that reflects how much traffic is using a link– Number is determined dynamically and is expressed as a fraction of 255

The lower the fraction the less the load on the link


EIGRP Metric CalculationUsing the Bandwidth Command

Modifying the interface bandwidth

-Use the bandwidth command-ExampleRouter(config-if)#bandwidth kilobits

Verifying bandwidth –Use the show interface command

Note – bandwidth command does not change the link’s physical bandwidth


EIGRP Metric Calculation The EIGRP metric can be determined by examining the

bandwidth delay


EIGRP Metric Calculation

EIGRP uses the lowest bandwidth (BW)in its metric calculation

Calculated BW = reference BW / lowest BW(kbps)

Delay – EIGRP uses the cumulative sum of all outgoing interfaces

Calculated Delay = the sum of outgoing interface delays

EIGRP Metric = calculated BW + calculated delay








DUAL Concepts

The Diffusing Update Algorithm (DUAL) is used to prevent looping


DUAL Concepts Successor

The best least cost route to a destination found in the routing table

Feasible distanceThe lowest calculated metric along a path to a destination network


DUAL ConceptsFeasible Successors, Feasibility Condition & Reported

Distance

Feasible Successor

-This is a loop free backup route to same destination as successor route


DUAL Concepts

Reported distance (RD)

-The metric that a router reports to a neighbor about its own cost to that network

Feasible Successors, Feasibility Condition & Reported Distance


DUAL Concepts

Feasibility Condition (FC)

-Met when a neighbor’s RD is less than the local router’s FD to the same destination network


DUAL Concepts

EIGRP Topology Table dissected


DUAL ConceptsTopology Table: No Feasible Successor A feasible successor may not be present because the

feasibility condition may not be met-In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance


DUAL Concepts


DUAL Concepts Finite Sate Machine (FSM)

–An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states–FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events


DUAL Concepts

DUAL FSM–Selects a best loop-free path to a destination–Selects alternate routes by using information in EIGRP tables


DUAL ConceptsFinite State Machines (FSM)

To examine output from EIGRP’s finite state machine us the debug eigrp fsm command


More EIGRP Configurations

The Null0 Summary Route By default, EIGRP uses the Null0 interface to discard

any packets that match the parent route but do not match any of the child routes

EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist

–One or subnets exists that was learned via EIGRP–Automatic summarization is enabled


More EIGRP ConfigurationsThe Null0 Summary Route



Disabling Automatic Summarization The auto-summary command permits EIGRP to

automatically summarize at major network boundaries The no auto-summary command is used to disable

automatic summarization–This causes all EIGRP neighbors to send updates that will not be automatically summarized

this will cause changes to appear in both -routing tables -topology tables



Manual Summarization

Manual summarization can include supernetsReason: EIGRP is a classless routing protocol & include subnet mask in update

Command used to configure manual summarization –Router(config-if)#ip summary-address eigrp as-number

network-address subnet-mask


More EIGRP Configurations Configuring a summary route in EIGRP



EIGRP Default Routes

“quad zero” static default route-Can be used with any currently supported routing protocol-Is usually configured on a router that is connected a network outside the EIGRP domain

EIGRP & the “Quad zero” static default route–Requires the use of the redistribute static command to disseminate default route in EIGRP updates


More EIGRP ConfigurationsFine-Tuning EIGRP

EIGRP bandwidth utilization-By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information-The command to change the percentage of bandwidth used by EIGRP is

Router(config-if)#ip bandwidth-percent eigrp as-number percent


More EIGRP Configurations Configuring Hello Intervals and Hold Times

-Hello intervals and hold times are configurable on a per-interface basis-The command to configure hello interval is

Router(config-if)#ip hello-interval eigrp as-number seconds

Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval

-The command to configure hold time value isRouter(config-if)#ip hold-time eigrp as-number seconds


Summary Background & History

–EIGRP is a derivative of IGRPEIGRP is a Cisco proprietary distance vector routing protocol released in 1994

EIGRP terms and characteristics–EIGPR uses RTP to transmit & receive EIGRP packets–EIGRP has 5 packet type:

Hello packetsUpdate packetsAcknowledgement packetsQuery packetsReply packets

–Supports VLSM & CIDR


Summary

EIGRP terms and characteristics–EIGRP uses a hello protocol

Purpose of hello protocol is to discover & establish adjacencies

–EIGRP routing updatesAperiodicPartial and boundedFast convergence


Summary

EIGRP commands–The following commands are used for EIGRP configuration

RtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-number

–The following commands can be used to verify EIGRPShow ip protocolsShow ip eigrp neighborsShow ip route


Summary

EIGRP metrics include–Bandwidth (default)–Delay (default)–Reliability–Load


Summary DUAL

–Purpose of DUALTo prevent routing loops

–SuccessorPrimary route to a destination

–Feasible successorBackup route to a destination

–Feasible distanceLowest calculated metric to a destination

–Reported distanceThe distance towards a destination as advertised by an upstream neighbor


Summary Choosing the best route

–After router has received all updates from directly connected neighbors, it can calculate its DUAL

1st metric is calculated for each route2nd route with lowest metric is designated successor & is placed in routing table3rd feasible successor is found

–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance–Feasible routes are maintained in topology table


Summary

Automatic summarization–On by default–Summarizes routes on classful boundary–Summarization can be disabled using the following command

RtrA(config-if)#no auto-summary


© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 70

EIGRP


EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol based on IGRP.

EIGRP supports CIDR, and hence VLSM.

Compared to IGRP, EIGRP boasts faster convergence times, improved scalability and superior handling of routing loops.

Technically, EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. Some of OSPF’s best traits, such as partial updates & neighbor discovery, are similarly put to use by EIGRP.


EIGRP

Recall that OSPF’s strengths include scalability and multi-vendor support. So if your core routers are a mixed bag of products from several different vendors, OSPF and RIP may be your only options.

But OSPF’s benefits, especially it’s hierarchical design, come at a price: administrative complexity.

EIGRP is an ideal choice for large, multiprotocol networks built primarily on Cisco routers (says Cisco).


Comparison of OSPF and EIGRP

OSPF EIGRPSupports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery.

Supports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery

Enables the admin to define route summarization.

Uses automatic route summarization & user-defined route summaries.

Is an open standard; has multi-vendor support

Is proprietary; can only be used with Cisco routers.

Is scalable; admin defined ‘areas’ provide manageable hierarchy.

Is scalable; no hierarchical domains exist

Is difficult to implement Is easy to implement.


EIGRP and IGRP Compatibility

EIGRP offers multiprotocol support and IGRP does not.

EIGRP scales IGRP’s metric by a factor of 256. That’s because EIGRP uses a metric that is 32 bits long, & IGRP uses a 24-bit metric. By dividing or multiplying by 256, EIGRP can easily exchange information with IGRP.

EIGRP imposes a max hop limit of 224, where IGRP has 255.


Sharing or redistribution, is automatic between IGRP & EIGRP as long as both processes use the same AS number.

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

Where by default: K1 = 1 K2 = 0 K3 = 1 K4 = 0 K5 = 0

EIGRP and IGRP Compatibility


EIGRP tags routes learned from IGRP as external because they did not originate from EIGRP routers. External EIGRP routes are denoted by EX in the routing table.

But IGRP cannot differentiate between internal & external routes

EIGRP vs. IGRP


EIGRP

EIGRP is an advanced distance vector routing protocol, but has advantages over simple distance vector protocols:

• rapid convergenceBy using an routing algorithm, Diffusing Update Algorithm (DUAL) which guarantees loop-free operation & allows all routers involved in a topology change to synchronize at the same time.

• partial bounded updatesEIGRP routers make partial, incremental updates, & unlike OSPF, the routers send these partial updates only to the routers that need the information. This is called bounded updates.


EIGRP cont.• minimal consumption of bandwidth when the network is stable

•No timed routing updates - instead small hello packets. •Exchanged a regular intervals •don’t use a significant amount of bandwidth.

• support for VLSM and CIDR• multiple network-layer support

EIGRP supports IP, IPX and AppleTalk via protocol-dependent modules (PDM).

• complete independence from routed protocolsPDM protect EIGRP from painstaking revision.


EIGRP Terminology & Tables

EIGRP routers keep route and topology information in RAM for quick access.

EIGRP terms and tables:neighbor tableMaintains a neighbor table that list adjacent routers. There is a neighbor table for each protocol that EIGRP supports.

topology tableTopology table for each configured network protocol. All learned routes to a destination are maintained in the topology table.

routing tableEIGRP chooses the best (successor) routes to a destination from the topology table & places these routes in the routing table.


successora route selected as the primary route used to reach a destination. Successors are kept in the routing table.

feasible successorIs a backup route. They are kept in the topology table.

EIGRP routers establish adjacencies with neighbor routers by sending hello packets, sent every 5 seconds (default).

By forming adjacencies, EIGRP routers do the following:

• dynamically learn of new routes that join their network

• identify routers that become either unreachable or inoperable

• rediscover routers that had previously been unreachable.

EIGRP Terminology


EIGRP Technologies cont.

Reliable Transport Protocol (RTP) is a transport layer (layer 4) protocol that can guarantee ordered delivery of EIGRP packets to all neighbors. To stay independent of IP, EIGRP uses its own proprietary transport-layer protocol to guarantee delivery of routing information.

EIGRP uses RTP to provide reliable or unreliable service as the situation warrants. Hello packets are not required to be reliable delivery. RTP supports both unicasting & multicasting , and it can multicast and unicast to different peers simultaneously.

The centerpiece of EIGRP is DUAL, the EIGRP route calculation engine. It uses a finite state machine.

DUAL tracks all the routes advertised by neighbors and uses the composite metric of each route to compare them. DUAL also guarantees that each path is loop-free.


EIGRP Technologies cont.

A successor is a neighboring router that is currently used for packet forwarding; it provides the least cost route to the destination and is not part of the routing loop

A feasible successor provides the next lowest cost path without introducing routing loops.


EIGRP Data Structure

Neighbor TableRouting TableTopology Table

Reported distance (RD) Feasible distance (FD)



Neighbor Tablethe most important table in EIGRP. The neighbor relationships in the neighbor table are basis for all EIGRP routing updates and convergence activity. supports reliable, sequenced delivery of packets.

Routing TableContain the routes installed by DUAL as the best loop free paths to a given destination. It canmaintain up to 4 routes per destination.Topology Tablestores all the information it needs to calculate a set of distances and vectors to all reachable destinations.



Reported distance (RD) The distance reported by an adjacent neighbor to a specific destination.

Feasible distance (FD) The lowest calculated metric to each destination.

Table is sorted with the successor routes at the top, followed by feasible successors.

At the bottom are what DUAL believes are routing loops.


To see the topology table, use the command:

Router# show ip eigrp topology [all]

Example of output:

P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33

via 10.2.0.2 (2681856/2169856), Serial1

Viewing (2681856/2169856), 2681856 is the FD, and 2169856 is the RD.

If no feasible successors to the destination exist, DUAL places the route in the active state.

Entries in the topology table can be in one of 2 states• passive route – route that is stable and available for use

• active route – route in the process of being recomputed by DUAL.


Internal routes originate from within the EIGRP AS.

External routes originate from outside the system.

Routes learned (redistributed) from other routing protocols such as RIP, OSPF and IGRP are external.

Static routes originating from outside the EIGRP AS and redistributed inside are also external routes.

NOTE:

The internal administrative distance of EIGRP is 90.


EIGRP Packet Types

EIGRP relies on 5 packet types to maintain its various tables and establish complex relationships with neighbor routers.

The 5 packet types:1. Hello2. Acknowledgment3. Update4. Query5. Reply


Hello PacketsEIGRP relies on hello packets to discover, verify & rediscover neighbor

routers. The default hello interval depends on the bandwidth of the interface:

Bandwidth Example Link Default Hello Default HoldInterval Time

Less than 1.544Mbps Multipoint Frame Relay 60 sec 180 sec

Greater than 1.544Mbps T1, Ethernet 5 sec 15 sec

Keep the hold timer 3 times the hello interval. EIGRP hello packets are multicast. On IP networks,

EIGRP routers send hellos to the multicasts IP address 224.0.0.10.

Recall that OSPF requires neighbor routers to have the same hello & dead intervals to communicate. EIGRP has no such restriction.


Acknowledgement Packets

An EIGRP router uses acknowledgement packets to indicate receipt of any EIGRP packet during a reliable exchange.

To be reliable, a sender’s message must be acknowledged by the recipient.

Hello packets are always sent unreliable, & require no acknowledgement.

Update Packets

Update packets are used when a router discovers a new neighbor. They are also used when a router detects a topology change.

All update packets are sent reliably.


Query and Reply Packets

EIGRP routers use query packets whenever they need specific information from one or all of its neighbors. A reply packet is used to respond to a query.

Query can be multicast or unicast

Replies are always unicast.

Both packet types are sent reliably.


EIGRP Convergence (DUAL)

DUAL’s sophisticated algorithm results in EIGRP’s exceptional fast convergence, says Cisco

A router’s topology table includes a list of all routes advertised by the neighbors. For each network, the router keeps the real (computed) cost of getting to that network & also keeps the advertised cost (reported distance) from its neighbor.


The best path is the path with the lowest metric route that is calculated by adding the metric between the next-hop router and the destination (the reported distance) to the metric between the local router and the next-hop router.

This computed cost, or distance is the FD.

The next-hop router(s) are selected as the best path is the successor. If several routes have the same FD, then there can be several successors to a destination.

EIGRP Convergence (DUAL)


RTA

RTX

RTZ

FDDI

Network24

RTY

COST

Serial10

100 100

10

20

1

Neighbor Computed Cost to 24 Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220

10

For RTA, RTY is the successor to Network 24, because it has the lowest computed cost (31). Hence RTA’s FD=31.

If RTY goes down, then is there a feasible successor – or not? If so, what is it?

RTA reaches Network 24 via:


RTA

RTX

RTZ

FDDI

Network24

RTY

COST

Serial10

100 100

10

20

1

Neighbor Computed Cost to 24 Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220

10

Feasible successor =

1. It’s RD < RTA’s FD AND2. Has the lowest computed cost of all other routes

DUAL calculates the feasible successor to be through RTX

Remember: RTA’s FD=31


RTA

RTX

RTZ

FDDI

Network24

RTY

COST

Serial10

100 100

10

20

1

Neighbor Computed Cost to 24 Reported Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220

10

Feasible successor =1. It’s RD < RTA’s FD AND2. Has the lowest computed cost of all other routes

Suppose RTX also goes down. Is there a feasible successor for RTA to Network 24?

NO! DUAL will set the route to Network 24 from passive to active state, and RTA will query its neighbor’s about Network 24 again.


Consider the output from the command ‘show ip eigrp topology all’:

P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33via 10.2.0.2 (2681856/2169856), Serial0via 10.2.1.2 (2681856/2169856), Serial1via 10.2.2.2 (2891856/2769856), Ethernet 0

Remember:Successor is the route that has the best lowest cost or FD.Feasible successor =

It’s RD < link’s FD AND has the lowest computed cost of all other routes


Consider the output from ‘show ip eigrp topology all’:

P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33via 10.2.0.2 (2681856/2169856), Serial0via 10.2.1.2 (2681856/2169856), Serial1via 10.2.2.2 (2891856/2769856), Ethernet 0

What are the successor(s)?

10.2.0.2 AND 10.2.1.2

What are the feasible successor(s)?

NONE


EIGRP Operation

The 4 key steps to EIGRP operation are:1. building the neighbor table2. discovering routes3. choosing routes4. maintaining routes

Choose the routes based on these 5 factors:1. bandwidth2. delay3. reliability4. load5. MTU (maximum transmission unit)

So, unless otherwise configured by an administrator, bandwidth & delay are the only 2 factors that determine EIGRP’s metric value.


Configuring EIGRP

Configuring EIGRP for IP Networks

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

Router(config-router)# network network-number

network-number is the NETWORK address of the interface of the router


Configuring EIGRP

The ip bandwidth-percent command configures the percentage of bandwidth that EIGRP can use on an interface.

By default, EIGRP is set to use up to 50 percent of the bandwidth of an interface to exchange routing information.

The command relies on the bandwidth of an interface.

Some cases the engineer sets the bandwidth to a lower number than the actual bandwidth of the link (in order to manipulate the routing metric).


Summarizing EIGRP routes for IP

EIGRP automatically summarizes routes at a classful boundary.For discontiguous subnetworks, you do NOT want summarization.The command that turns summarization off on EIGRP is:

Router(config-router)# no auto-summaryHence, with summarization turned off, EIGRP routers will advertise subnets.


Manual summary routes are configured on a per-interface basis by:

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

By default, EIGRP summary routes have an administrative distance of 5. The value can range between 1 and 255.

Summarizing EIGRP routes for IP


What did I Learn from chapter 9?

Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).

Examine the basic EIGRP configuration commands and identify their purposes.

Calculate the composite metric used by EIGRP.

Describe the concepts and operation of DUAL.

Describe the uses of additional configuration commands in EIGRP.


ENDEIGRP

NextLink State Routing Protocols

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